Institute for Crustal Studies
1997/98 Annual Report

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Awards Administered

Crustal Materials Crustal Structure and Tectonics Earthquakes Hazardous Waste

Crustal Materials:

Wendy Bohrson
Frank Spera

2/1/95 - 1/31/99 $85,656

National Science Foundation, EAR-9418720

Processes and Rates of Compositional Zonation in Crustal Magma Bodies: Constraints from High-precision U-Th Disequilibria

The Campanian ignimbrite is an 80 km , moderately welded alkali trachyte located near Naples, Italy. The petrology and U-Th disequilibria characteristics of this explosively-generated deposit have been studied through major and trace element analyses (~15) as well as high-precision Th isotopic analyses (~12). These data indicate that this young deposit derived from a zoned magma body that experienced high-level crustal contamination; the most likely contaminant is hydrothermally-altered volcanic basement. Additional Th work, in the form of mineral isochrons, is underway to determine the timing and extent of this contamination process. In addition, the first high-precision Ar/39 Ar ages of the deposit have been generated, dating the deposit at ~39,000 years. Additional Ar analyses are now underway to address questions raised by recent field work: an older ignimbrite, separated from the "classic" Campanian by a soil, has been discovered, and the new Ar analyses will assess the age of this unit. The results could be very important because this older unit may represent a previously unidentified explosive eruption in the Naples area; such information would be crucial to accurate assessments of volcanic hazard in this densely populated region of Italy.

This grant also supported theoretical work by Bohrson and Spera about the nature of magma-wallrock interaction, specifically the process of assimilation-fractional crystallization (AFC). AFC is governed by the laws of conservation of mass, energy, and species. Prior to the work Bohrson and Spera are currently doing, assessment of this process had been limited to treatments that considered conservation of mass and species. The addition of conservation of energy has dramatically changed the theoretical chemical trends associated with the process of AFC; a review of the literature, currently underway, suggests these findings may explain data sets that were previously only poorly explained by traditional AFC modeling. In addition, some of the long-held assumptions about the process of AFC have been shown to be incorrect by this new formulation (Spera and Bohrson, 1997; Bohrson and Spera, 1997).


Frank Spera

12/15/97 - 12/14/98 $467,361

Department of Energy, DE-FG03-91ER14211

Collaborative Research: Magma Rheology, Mixing of Rheological Fluids, Molecular Dynamics Simulation, and Lithospheric Dynamics

Our aims are (1) experimental rheological measurements of magma including melts, melt-vapor emulsions and crystal-melt suspensions (2) Molecular Dynamics (MD) simulations of molten and glassy silicate and aluminosilicate geomaterials with emphasis on understanding the connection between atomic structure and properties at temperatures and pressures characteristic of continental lithosphere (3) high resolution simulation of thermohaline convection in low-porosity geomedia (4) development of geochemical models for the evolution of crustal magma bodies undergoing simultaneous assimilation, fractional crystallization, periodic recharge and periodic eruption that incorporate energy conservation in addition to total and species mass conservation.

This collaborative project with D. A. Yuen at the University of Minnesota, Minneapolis will promote our understanding of the thermal, chemical, mechanical and rheological states of the continental crust and subcrustal lithosphere with particular emphasis on the nonlinear interactions among the various subsystems including hydrothermal and magmatic components. Our workplan encompasses the following (1) determination of the structure and property of melts by MD simulations of multicomponent systems. (2) Molecular Dynamics of mesoscale fluid-dynamical phenomenon in the range of tens of microns, specifically for two-fluid and chemically reacting systems (3) mixing processes of rheological fluids in convection and visualization of complex processes (4) shear zones in faulting from grain-size rheology (5) development of stress fields and faulting (6) numerical modeling of heat and mass transport driven by thermal and chemical heterogeneity's in hydrothermal-magmatic systems (7) experimental rheometric measurements of magma at high temperatures and development of non-linear constitutive relations.

The results reported below are the UC Santa Barbara part of this project. Additional results can be found in the summary of activities by the University of Minnesota team led by D. A. Yuen. Construction of a novel custom high temperature rheometer based on a concentric cylinder design has been completed. This device can investigate the rheology of magma, a complex mixture of solids, melt and vapor bubbles, at temperatures from 700 °C to 1375 °C for shear rates in the range 10-5 to 1 s-1. The instrument has been calibrated and certified using NBS standard borosilicate and lead silicate compositions; we can measure the viscosity of these melts to within 0.02 log10 units. This 2-sigma uncertainty is better than the NBS quoted value of 0.029 log10 units. A paper is in press in the journal Review of Scientific Instruments that details the salient features of the design, fabrication and certification of this device. Experiments are presently underway exploring the relative viscosity, defined as the ratio of the viscosity of the mixture to the viscosity of single phase melt for a rhyolite from the DOE sponsored drilling site at Obsidian Dome, near Long Valley California as well as melt-vapor emulsions of molten albite and molten orthoclase compositions. There are essentially no previous measurements for the viscosities of these magmatic emulsions with vapor contents in the range 0 to circa 50 volume percent. Preliminary results suggest the presence of a percolation threshold of about 10 to 20 volume percent beyond which the mixture (relative) viscosity depends upon vapor content rather strongly and (2) a critical shear rate exists such that for g > g crit the relative viscosity decreases with increasing bubble loading whereas at shear rates less than the critical value the relative viscosity increases with bubble content. The goal of this work is to develop comprehensive non-linear constitutive relations for melt-vapor emulsions in the range of shear rates and temperatures relevant to crustal magmas. We also plan to investigate solid-melt mixtures. Other work completed this year includes an extensive set of MD simulations applicable to molten and glassy CaAl2Si2O8 at temperatures and pressures characteristic of continental lithosphere. Subducting crust is rich in anorthite component and the goal of these studies has been to explore the atomic structure of this melt especially the relationship between its changing structure and its macroscopic thermodynamic and transport properties. This work is currently in press in the journal American Mineralogist . Other MD simulations for compositions in the system NaAlO2-SiO2 have also been carried out; we have shown that MD results may be used in combination with the analytic theory of Adams-Gibbs-DiMarzio (AGD) to predict the variation of oxygen self-diffusion as a function of pressure, temperature and composition in this model crustal system. A third sub-project that is in progress is the development of a geochemical model that takes energy conservation into explicit account to forward model the geochemical evolution of crustal magma bodies that are undergoing simultaneous assimilation, fractional crystallization, recharge and eruption. This work is now being written up and two papers detailing it will be submitted by December 1998. Results have already been presented at the AGU Fall 1997 meeting. Finally, high-resolution simulations of the dynamics of thermohaline convection in saturated porous media have been completed. We have confirmed the earlier work of Spera and Yuen that in low porosity geologic media that a doubly-advective instability sets in that leads to chaotic behavior for Darcy Rayleigh numbers and buoyancy ratios in the range found in nature. These simulations take account of the temperature and composition dependence of fluid properties (H2O +NaCl) and allow for the importance of dispersion (rather than simple molecular diffusion) of solute. This doubly-advective instability has application to diagenesis, the formation of crustal ore deposits and the evolution of metamorphic terrains. This work is being written up for submission to Earth and Planetary Science Letters and Science and we will present some results at the Fall 1998 AGU meeting in San Francisco.


Frank Spera
Alain Trial

7/1/96 - 12/30/98 $70,000

National Science Foundation, EAR-9627800

Collaborative Research: Role of Shear Heating in the Generation and Ascent of Granitic, Basaltic, and Komatiitic Magma

A model has been set up to look at the geochemical evolution of magma bodies undergoing simultaneous assimilation, fractional crystallization, magma recharge and magma venting or eruption. This model explicitly incorporates energy conservation and provides information regarding the path magma follows as thermal equilibration is approached. The model itself is a set of 5 coupled non-linear ordinary differential equations solution of which gives the magma temperature, assimilant temperature, fraction of magma, mass of cumulates and the isotopic and trace element composition of the magma including oxygen isotopic ratios as equilibrium is approached.


Frank Spera
Daniel Stein

3/1/97 - 2/28/99 $86,210

National Science Foundation, EAR-9614376

Experimental Rheometry of Magmatic Multiphase Suspensions

During 1998 this project entered its operational phase as the new computer-controlled magma rheometer produced its initial results. Measurements conducted on a high-temperature viscosity standard material have verified that the instrument recovers the published values for the reference standard within the published precision. A full description of the instrument and its component systems, as well as the results for the standard, has been published in "The Review of Scientific Instruments". Additional measurements of a synthetic liquis material of composition near that of the mineral phase orthoclase (microcline) feldspar have also been conducted and the results are consistent with those produced in other laboratories.

Significant progress has been realized in the quest to provide the first high-precision rheological measurements on concentrated silicate magmatic gas-liquid emulsions at geologically-realistic shearing rates. Reliable techniques for preparing magmatic emulsions with as much as 60 volume percent of vapor phase have been developed. The liquid phases to be used consist of 1) A natural rhylolite obsidian from the Mediterranean Island of Lipari and 2) Liquids near in composition.

In the experiments to be conducted, silicate liquids containing suspensions of vapor bubbles held at high temperatures are sheared between the concentric, counter-rotating cylinders of the rheometer's sample assembly. Viscosity in these multi-phase materials is expected to vary with the experiment temperature, the shearing rate, and volume fraction of bubbles, perhaps in an intricate manner.

Data obtained in this study will lead to significant progress in understanding the complex rheological behavior of magmatic systems and their consequent natural hazards.


Frank Spera
Wendy Bohrson

3/15/97 - 2/28/99 $81,000

National Science Foundation, EAR-9614381

Isotopic and Petrological Constraints on Magma Dynamics at Mt. Etna

Previous work has established that there are large variations in chemical and isotopic compositions in historical and ancient eruptions from Mt. Etna, Italy. We are addressing this matter in more detail using state-of-the-art geochemical and isotopic techniques.

The first phase of the work is now complete: study of the 500 ka to 100 ka record (Bryce et al. , 1997, Bryce et al. , 1998, Bryce, 1998). Results indicate that Etna changes from a dominantly tholeiitic fissure volcano to a mildly alkalic composite volcano where central eruptions dominate. The change occurred over a 100 ka interval, starting around 200 ka and ending around 85 ka. Detailed modeling indicates that the geochemical and isotopic characteristics of the mantle source region from which Etnean magmas were extracted changed discontinuously. The data suggest that the source region may have experienced carbonatite metasomatism, that extensive fractional crystallization affected the magmas, and that some limited alkali enrichment, perhaps due to assimilation of crustal material, may have also occurred. This study represents the Ph. D. dissertation of Julia Bryce, who completed her degree in August 1998. She is now preparing the data and interpretations for submission to peer-reviewed journals.

Historical lavas from Mt. Etna record distinct changes in particular geochemical characteristics with time. Interpretations of the causes of these changes range from mantle heterogeneity to crustal contamination. We have undertaken a detailed characterization of the size distribution, chemical and isotopic composition of phenocrysts and microphenocrysts from a number of key historical eruptions. Petrographic descriptions, electron microprobe work and crystal-size distribution analyses are currently underway. These will be followed by detailed microsampling of individual phenocrysts for Sr and Pb isotopes. Our results will provide constraints on mantle-dominated vs. crust-dominated models for the chemical and isotopic variations, and on processes of magma formation, storage and ascent through the continental crust.

Crustal Structure and Tectonics:

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Cathy Busby

1/1/98 — 8/31/00 $60,000

American Chemical Society — Petroleum Research Fund, 32624-AC8

High Resolution Sequence Stratigraphic Framework of a Tectonically Active Forearc Basin

Mesozoic rocks of the Baja California Peninsula form one of the best-exposed and most areally extensive, well preserved convergent margin complexes in the world. Busby proposes that this convergent margin shows an evolutionary trend that is typical of arc systems facing large ocean basins: a progression from highly extensional through mildly extensional to compressional strain regimes. This proposal focuses on the southernmost end of the Peninsular Ranges forearc basin complex of southern California and northern Baja California, Mexico, the Rosario embayment. Busby suggests that the Peninsular Ranges forearc basin complex formed as forearc strike slip basins under a compressional convergent margin strain regime, where strong coupling promoted the development of strike slip faults during oblique subduction. Strike slip basins are known to be the most tectonically active and complex basin type of all, characteristically showing very rapidly alternating subsidence, uplift and titling events of great magnitude. This makes them ideal for the kind of detailed "tectono-stratigraphic analysis" that is proposed here. Busby and a graduate student will spend 3 to 4 months in the field mapping the entire basin at a scale of 1:50,000 or better using aerial photographs, satellite imagery and topographic bases. Packages of strata will then be dated using foraminifera, nannofossils, macrofossils and magnetostratigraphic data.


Jordan Clark
Bruce Luyendyk

7/1/97 - 6/30/99 $24,300

UC Energy Institute, 08970725

Measurement of Natural Marine Hydrocarbon Seepage Using an Atmospheric Tracer Method

Natural marine hydrocarbon seeps near Coal Oil Point, Santa Barbara County, CA, pollute the coastal ocean and regional atmosphere. Chemical signatures from these seeps can be followed for 100s of kilometers away from the point. Potentially, the most serious consequence of seepage is its relationship with the formation of ozone. The seeps are significant sources of reactive organic gases (ROGs) which are precursors to ozone. Although they are poorly constrained, estimates of the total flux of ROGs from these seeps are of the same order of magnitude as the total anthropogenic source in this county and may be substantially larger than the value currently used by the local air pollution control board. It is critical for policy makers to have accurate estimates of all sources of ROGs including natural sources so that they can assess the likely impact of further economic development on air quality in Santa Barbara County and so they can develop realistic air quality goals. Our project will attempt to quantify the total emission rate of ROGs to the local atmosphere by conducting atmospheric gas tracer experiments above an intense area of seepage at the eastern end of the Coal Oil Point seep field. The results for these experiments will provide a calibration for high resolution digital sonar surveys (3.5 and 12 kHz) which determined the relative flux of hydrocarbons from the entire seep field. Two tracer experiments were completed during May and June and a third experiment which will be conducted in conjunction with a new high resolution sonar survey is planned for late September. This project is a part of on-going research which is focused on determining methods of quantifying natural marine seepage and identifying the effects of oil production on seepage rates.


Phil Gans
Wendy Bohrson

9/1/95 - 8/31/98 $20,072

National Science Foundation, EAR-9506687

Petrologic Evolution of the Northern Eldorado Mountains, Southern Nevada

The lower Colorado River extensional corridor in southern Nevada, western Arizona, and southeastern California records in exquisite detail the volcanic and structural evolution of a failed propagating continental rift, making it an ideal natural laboratory to examine the interplay between continental extension and magmatism. Large magnitude extension (i. e. ³ 100%) within this corridor is indicated by pervasive normal faulting and tilting of Miocene volcanic and sedimentary rocks, by unroofing of mid-crustal metamorphic and plutonic rocks, and by crustal thinning (from ~40-45 km to ~25-30 km). For any given area within the corridor, 4-8 m. y. of voluminous mafic to silicic volcanism is accompanied, in part, by regional extension. The inception of volcanism preceded the inception of major extension, and distinct differences in pre-, syn-, and post-extensional eruptive volumes have been documented. The Eldorado Mountains record a suppression of volcanism during and following high-magnitude extension which may be related to the effects of normal faulting in the shallow crust (Gans and Bohrson, 1998).

A petrologic investigation of the northern Eldorado Mountains is currently underway to document tectono-magmatic interactions in a continental rift. Changes in major and trace element (~30 analyses) compositions of mafic volcanic rocks erupted prior to, during, and after large-magnitude extension indicate that there may be variations in the relative contributions of asthenosphere and lithosphere as extension waxes and wanes. Trace element evidence suggests that pre- and syn-extensional magmas may be largely derived from the lithosphere, whereas post-extensional magmas appear to have a significant contribution from the asthenosphere. Isotopic work (Sr, Nd, Pb) currently in progress indicates that the lithosphere has contributed extensively to most if not all of the lavas. Documenting the relative contributions of crust, lithospheric mantle, and asthenospheric mantle is essential for understanding how the structure of the upper mantle and crust changes during high-magnitude extension.


Bradley Hacker

4/1/98-3/31/99 $49,988

National Science Foundation, EAR97-28643

Xenoliths from the North-Central Tibetan Plateau- INDEPTH III Geologic Team

During a geologic transect across the Qiangtang terrane, INDEPTH III geologists discovered xenoliths, the first reported from the Tibetan plateau, at three separate localities in the area of 34° 24'N, 89°14'E. The host rocks are moderately porphyritic felsic lava flows interlayered with basaltic lava flows. The relatively fresh trachyandesite to trachyte host rocks are characterized by high K2O (K2O/Na2O=1.5-2.0) and therefore belong to the shoshonitic series. Phenocrysts include An30 plagioclase, An05Or56Ab36 sanidine, quartz, pargasite, and abundant phlogopite, monazite and apatite; the holocrystalline groundmass is dominated by sanidine, phlogopite, ilmenite, titaniferous magnetite, and apatite.

Whereas the basalts contain only extremely rare xenoliths, the more evolved flows contain readily visible mm- to cm-size xenoliths and xenocrysts. The xenocrysts are chiefly sanidine, garnet, and quartz. The most abundant xenoliths are granulite-facies rocks with garnet + enstatite + plagioclase + phlogopite + apatite + hercynite + monazite. Less common are phlogopite websterite, phlogopite gabbronorite, garnet + plagioclase + tourmaline + quartz granulite, and augite + pargasite + plagioclase + monazite + apatite amphibolite.

Partitioning of Fe and Mg between coexisting augite and enstatite indicates xenolith equilibration temperatures of c. 1000°C, and Al partitioning between garnet and enstatite indicates pressures of 1.3-1.5 GPa, equivalent to extraction depths of c. 40-55 km. These calculated PT conditions are compatible with the presence of kyanite inclusions in garnet, which requires pressures >1.4 GPa at 1000°C. Textural evidence of the decompression reaction, garnet (alm57prp36grs05sps03) + opx (4.8% Al2O3) + Na-cpx --> opx (7.6% Al2O3) + hercynite + magnetite + oligoclase, is widespread.

Volcanic rocks nearby have yielded ages of c. 1 and 8 Ma (Turner et al. , 1997), suggesting that the xenolith-bearing flows were erupted since the Late Miocene. Teleseismic P waves recorded in Tibet indicate that the crust of the Qiangtang terrane is c. 65 km thick (Owens and Zandt, 1997), implying that these xenoliths are samples of the lower crust.


Jeff Lee

6/1/95 - 6/30/99 $62,356

National Science Foundation, EAR-9526016

Quaternary Evolution of the Eastern California Shear Zone between Latitudes 36 degrees and 39 degrees

Geologic mapping along the Towne Pass fault as well as surveying of topographic profiles, using a Leica Total Station, across the most recent fault scarp was completed. The mapping indicates that the western end of the Towne Pass fault is an older normal fault; movement is Miocene to Pliocene in age and there is no evidence for Quaternary faulting. Surveying of 3 beheaded stream channels along the Owens Valley fault was also completed. The 2.4 m of vertical offset across the scarp and the 20 km long rupture was the result of a single earthquake event. Diffusion erosion modeling, using a numerical technique, of the surveyed profiles indicates that the fault scarp formed, hence the earthquake occurred, 7-12 thousand years ago. Moment magnitude associated with this earthquake is on the order of 6.7-6.9. Work over the next year will focus on trenching studies along the Deep Springs and White Mountains fault zone.


Jeff Lee
Phil Gans

4/1/96 - 3/31/99 $207,419

National Science Foundation, EAR-9526861

Geometry and Timing of Gneiss Dome Formation, Southern Tibet, China

This project combines field mapping, structural studies, metamorphic petrology, and geochronology to characterize and document the structural and tectonic evolution of gneiss domes in southern Tibet. This project is being completed with the collaboration of geologists from the Institute of Geology, State Seismological Bureau, Beijing. Last year we completed mapping of the Kangmar dome and this year our efforts focused on metamorphic petrology, U/Pb zircon geochronology, and Ar/Ar and fission track thermochronology of samples collected from this dome. The results of these analytical studies indicate that the rocks in the Kangmar Dome were buried to depths of 23 km and heated to temperatures as high as 625 ° C and exhumed rapidly between ~15 Ma and 10 Ma. These studies suggest that this gneiss dome is compressional in origin and formed simultaneously with the Southern Tibetan Detachment System.

In addition, this last spring we spent two months mapping, at 1:50,000 scale, the Majba Dome, which is located ~100 km to the west of the Kangmar Dome. We mapped a sequence of Paleozoic sedimentary rocks that grade downward into high grade metamorphic rocks, orthogneisses, and migmatites. We also identified two primary deformation events: (1) north-south compression resulting in open to isoclinal folds and superimposed on that (2) north-south extension resulting a domed mylonitic foliation and north-south stretching lineation. In addition, we mapped two post-tectonic granites. Numerous rock samples were collected for petrology, microscopic structural and kinematic analyses, U/Pb geochronology, and Ar/Ar and fission track thermochronology. Preliminary U/Pb geochronology suggests that one of the post-tectonic granites is 14.5±0. 1 Ma and therefore the deformational fabrics are pre-Middle Miocene. Work over the next year will concentrate on mineral separation for additional geochronology and thermochronology analyses, and compiling structural and field data.

Bruce Luyendyk

8/15/97 - 7/31/99 $99,659

National Science Foundation, OPP-9615281

Collaborative Research: Air-Ground Study of Tectonics at the Boundary Between the Eastern Ross Embayment and Western Marie Byrd Land, Antarctica: Basement Geology and Structure, and Influences on West Antarctic Glaciation

Structure at the boundary between the Ross Embayment and wMBL may be a result of 1) Cenozoic extension on the eastern shoulder of the Ross Sea rift, or 2) uplift and crustal extension related to Neogene mantle plume activity in wMBL; or a combination of the two. Faulting and volcanism, mountain uplift, and glacier downcutting appear to now be active in wMBL, where generally E-to-W-flowing outlet glaciers incise Paleozoic and Mesozoic bedrock, and deglaciated summits indicate a previous N-S glacial flow direction.

Our study will include aerogeophysics within a 400 x 400 km area using the NSF/OPP SOAR facility aircraft (Support Office for Aerogeophyscial Research) in the first season, now planned for 1998/99, combined with on-ground geology in this season and the following one. Our rationale for a combined program is the complete coverage of crustal-scale structure from the airborne geophysics, and mountain-range and outcrop scales from the geologic field work.

During this past year we accomplished two items: 1) We purchased and set up a SPARC Ultra workstation that will be used for processing SOAR aerogeophysical data; 2) Luyendyk traveled to SOAR camp at Siple Dome Antarctica for familiarization and planning. At Siple Dome Luyendyk worked with Don Blankenship and Jeff Williams of SOAR. The survey boundaries and grid were finalized. Plans were drawn up for the conduct of the survey in 1998/99. Luyendyk was introduced to quality control procedures and saw the process of obtaining data. Three flights were made into the survey region.

This next season (98/99) Luyendyk and Siddoway et al. will be stationed at Clark Camp in the Ford Ranges, Marie Byrd Land. Luyendyk will supervise the acquisition and QC for the aerogeophysics survey. Siddoway will lead a trail party to explore the southern Ford Ranges in a collaborative project.


Bruce Luyendyk

7/15/94 - 6/30/99 $175,536

National Science Foundation, OPP-9316712

Collaborative Research: Glacial Marine Stratigraphy in the Eastern Ross Sea and Western Marie Byrd Land, and Shallow Structure of the West Antarctic Rift

This is a collaborative project between Bruce Luyendyk at UCSB and Louis Bartek at the University of Alabama. We conducted a marine geology and geophysics study of the Cenozoic glacial and tectonic history of western Marie Byrd Land (wMBL), West Antarctica, in the region of the eastern Ross Sea, Edward VII Peninsula, and the Ford Ranges. The study region is located at the eastern edge of the Ross Sea and Ice Shelf. The offshore work proposed here used the icebreaker N. B. Palmer during January and February 1996. No marine geophysical data were available from this large region.

We are concerned with these main problems:

• What is the history of the West Antarctic ice sheet in this region?

• How are West Antarctic rifting and the glacial history related?

The offshore survey obtained multibeam echo soundings, high resolution seismic reflection data, gravity and magnetic profiles, and bottom samples. We also completed a site survey for the Cape Roberts Drilling Project in the western Ross Sea adjacent to the Transantarctic Mountains.

We contributed papers resulting from our preliminary studies to the Fall '97 national meeting of the American Geophysical Union (Hamilton et al. , 1997; Kluiving et al. , 1997; Luyendyk et al. , 1997).

The major features in the eastern Ross Sea include the Edward VII Peninsula and the Colbeck Trough offshore. The trough is up to 800-1000 m-deep, trends NNW for almost 100 kilometers, and is aligned with the Kiel Glacier onshore to the southeast. Near the ice shelf front the trough is devoid of sediment. Dredge hauls retrieved mylonitic rocks and cataclasites from the higher eastern wall. Farther to the NNW the trough is cut through glacial marine sediments. Multichannel seismic data here identify seismic stratigraphic sequences RSS1 and overlying RSS2 that have been previously mapped in the Ross Sea. RSS1 and RSS2 are separated by a major unconformity (U6?). NNE-SSW and NW-SE fault sets showing normal separation define grabens in acoustic basement holding RSS1. RSS2 is not deformed and has internal layers that are tilted westward. It is correlated with Late Oligocene and younger glacial marine sequence mapped elsewhere. Modeling of gravity data locates major north-trending basins cut into acoustic basement. Colbeck Trough does not cut the basement on the outer shelf. The trough is a glacial erosion feature that follows pre-existing NNW-trending half-grabens.

We conclude that the continental margin in the eastern Ross Sea was deformed by several episodes of Late Cretaceous normal faulting and received syn-rift sedimentation (RSS1). Denudation of western Marie Byrd Land during Late Cretaceous to Oligocene (?) time produced the West Antarctic Erosion Surface that may be present as one of the unconformities we mapped offshore (U6?). Subsequently, the RSS2 sequence was deposited in Late Oligocene to Early Miocene time. In Late Miocene to Recent time glaciers carved through northwest-trending grabens and RSS2 to form the Colbeck Trough and deposited glacial marine units onto the outer continental shelf. Dips in RSS2 and younger units record westward tilt of the continental margin. This regional tilting is interpreted as due to uplift of the plume-generated Marie Byrd Land dome to the east in Late Tertiary time.

During Palmer 9601 we completed a site survey for the Cape Roberts Drilling Project that includes over 250 km of multichannel (MCS) and high resolution single channel (SCS) seismic reflection. The objective of the survey was to obtain seismic coverage offshore Cape Roberts that could be used to site drilling locations for the Cape Roberts Project and to later tie sedimentary sequences away from core holes.

Three fault arrays were identified offshore Cape Roberts: two sets of rift border faults striking NW and NNE, and a third set of ENE trending faults, oblique to the northerly trend of the rift basin. Two igneous bodies, identified from magnetic anomalies and seismic data along the western margin of the basin, apparently resulted from magma ascending along pull-aparts where transfer faults cross-cut the main border fault on the west side of the Cape Roberts rift basin.

We propose that the activation of the rift border faults and subsequent subsidence of the Cape Roberts rift basin occurred during an episode of increased uplift in the TAM in Late Eocene time. Our interpretations of seismic reflection data identify an angular unconformity between the gently east-dipping synrift unit (V4a) and the more moderately dipping pre-rift units (V4b and V5). This sequence boundary is thought to correspond to the progressive opening of the Cape Roberts rift basin, associated with tilting and rotation of fault blocks along the eastern margin of the graben. The underlying pre-rift sequences in-fill the Victoria Land basin to the east; however, these sequences gradually thin to the west towards Roberts Ridge, suggesting that the formation of the Cape Roberts rift basin postdates the major rifting phases in the Western Ross Sea that formed the larger and deeper Victoria Land Basin.


Bruce Luyendyk

7/1/96 - 6/30/98 $23,500

UC Energy Institute, UCSB 08960643

Geophysical Investigation to Determine Impacts of Oil Production on Natural Hydrocarbon Seepage in the Santa Barbara Channel

Prolific natural hydrocarbon seepage offshore of Coal Oil Point in the Santa Barbara Channel, California contributes significant quantities of gaseous and liquid hydrocarbons to the local environment, and may also represent an important process at the global scale. Insight into rates of seepage improves the understanding of local pollution from seeps and global seepage potential. Constraining the volume of fluid migration in the crust associated with seepage is also relevant since such fluid movement can mark diagenetic processes and affect parameters of structural stability causing earthquake swarms. The distribution of gaseous seepage offshore of Coal Oil point was mapped using 3.5 and 50 kHz sonar by imaging rising seep gas bubbles which act as acoustic scattering targets within the water column. Examination of a series of mapped seep distributions reveals the following: (1) spatial location of seeps is principally controlled by structural features of the offshore geology, aligning with the east-west structural trends of anticline axes; (2) intensity of seepage emission correlates with structural relief and perhaps cross-cutting by faults; (3) both spatial distribution of seepage and volume emission rates vary over time; (4) drawing down of reservoir hydrocarbons and the reduction in reservoir pressure associated with offshore oil production is one contributing factor decreasing the extent of seepage and seep emission volumes; (5) areal extent of seep distribution within 13km 2 of platform Holly decreased from 0.9 to 0.4 km 2 and volumetric emission declined on the order of 50,000 m 3 /day between 1973 and 1995; (6) a current estimate of volumetric flux from seeps for the entire Coal Oil Point offshore area suggests emission is on the order of 1-2x10 5 m 3 of gas per day and 20,000-30,000 liters of oil.


William McClelland

07/01/95-06/30/97 $131,452

National Science Foundation, OPP-9423534

U-Pb Analysis of Detrital Zircon in Late Proterozoic Rocks of Arctic Alaska: Implications for Tectonic Evolution of the Canada Basin and Adjacent Polar Margins

The U/Pb detrital zircon study of Proterozoic metaclastic rocks in Arctic Alaska, designed to provide additional constraints on the tectonic evolution of the Canada Basin, initiated with a 3 week summer field program in 1995. A total of 32 samples spanning the 1200 km strike length of the Brooks Range orogen were collected for detrital zircon analysis. All of the samples have been processed by 6 undergraduate students supported by the REU grant. In addition, the students were provided with instruction in mineral separation techniques as well as several informal seminars concerning geochronological methods. To date, approximately 50 single zircon grains have been analyzed from 3 samples collected from the Proterozoic Nerukpuk Formation in the northeastern Brooks Range. On the basis of the initial detrital zircon ages, which range from 1.0 to 3.1 Ga, it appears that Proterozoic clastic rocks in the Brooks Range received sediment from non- North American sources. Additional analyses from the remaining samples will further understanding of the paleogeographic origin of northern Alaska and tectonic evolution of the Canada Basin.


Craig Nicholson
Marc Kamerling

4/17/97 - 10/16/98 $118,680

US Geological Survey, 1434HQ97GR0314

Acquisition of 3-D Subsurface Well Data & 3-D GIS for the Ventura Basin, California

In the Ventura Basin, faults and folds accommodate high rates of oblique crustal strain and uplift rates exceed 10 mm/yr. These faults represent a significant seismic hazard, yet much of what is 'known' about these faults and folds has been inferred from 2D balanced cross section models. To test the reliability of these 2D models to predict 3D subsurface structure, we are evaluating a unique 3D dataset provided by the Ventura Basin Study Group (VBSG). The VBSG study consists of 17 structure contour maps and 84 interlocking cross section data panels based on nearly 1200 correlated deep-penetration (1-5 km) wells. Many of these wells drill active fault and fold structures associated with major fault systems, including the San Cayetano, Oak Ridge, and Santa Susana faults. This integrated 3D study is based on wire-line logs, mud logs, paleontological reports, core analyses, and surface maps. Each data panel typically ties in 4 directions to define the sides of a 3D data volume or cell. The result is a 3D presentation of an enormous quantity of high-quality subsurface data that have been reconciled into a coherent geological interpretation. Any 2D or 3D kinematic model of the basin and its associated fault and fold geometry must incorporate these data, if it is to be successful.

This project consists of three parts: 1) acquiring the VBSG subsurface study, 2) developing an on-line digital database of these and other data for the Ventura Basin, and 3) creation of three-dimensional models of the structures within the Ventura Basin. This will help provide a basis for the understanding of the geometry, tectonic development, and seismic hazard of active fault structures in the Ventura Basin. Steps 1 and 2 are now complete and Step 3 is underway. The VBSG maps and cross sections have been digitally scanned and are now available to the public from our website at Higher resolution versions of the digital images are also available for research purposes. Once this stage is completed, the results of the VBSG study will be incorporated with other subsurface datasets and previous studies to create accurate 3D subsurface models for the active fault and fold structures in the Ventura Basin.


Nicholas Pinter
Chris Sorlien

7/1/97 - 6/30/99 $38,177

US Geological Survey, 1434HQ7GR03173

Slip on the Channel Islands-Santa Monica Mountains Thrust: Testing Models of Fault-Related Folding

During the past year, my students and I have continued work related to the tectonics and tectonic geomorphology of the Northern Channel Islands, supported by the National Earthquake Hazard Reduction Program (NEHRP) of the U. S. G. S. and by a collaborative award from the National Science Foundation. As discussed in last year's ICS Annual Report, the "thrust" of this research is using precisely-measured deformation of coastal terraces around the islands to infer the geometry and rates of slip on the reverse-fault structure that is believed to core the Northern Channel Islands trend. Field work was all-but-completed during 1997-98, with final mapping of terraces and terrace deposits around Santa Cruz and Anacapa islands. Finding the all-important terrace feature, the shoreline angle, continued to be a challenge in the field, but detailed work in virtually every canyon that incises the terraces has paid off. Shoreline angles were measured or tightly bracketed at sites over broad areas around the islands. Measurements were made using a laser total station tied to topographic benchmarks for elevation, and using a differentially-corrected (DGPS) positioning system for horizontal coordinates. In addition, elevations of stripped terrace remnants are being assessed using a series of algorithms to filter the DEMs of the islands, combined with statistical techniques to apply best-fit surfaces to the terrace remnants. All of the results from the DEMs are field-checked to rule out potential false signals from lithologic control or colluvial mantles.

Another challenge in this research is assigning ages to the different coastal-terrace levels. In addition to previous uranium-series results from solitary corals, we have completed amino-acid-racemization analyses of shells from terrace-capping sediments, radiocarbon analyses of shells (combined with scanning electron microscopy to identify recrystallization or other potential problems), and strontium-isotope tests will be attempted on at least some of the samples. The final stage of the research -- analysis of all field measurements, combined with age determinations, to give rates and patterns of deformation and to infer the geometry and slip rate on the underlying thrust fault(s) -- will be completed during the upcoming year.


Chris Sorlien

3/1/97 - 2/28/99 $22,735

National Science Foundation, EAR-9706258

Collaborative Research: Testing Models of Fault-Related Folding, Northern Channel Islands, California

Christopher Sorlien's part of the collaborative proposal has been to interpret the structure and stratigraphy of the shelf and slope between Santa Cruz-Anacapa islands and deep Santa Barbara basin. He also spent almost two weeks in the field on the islands in support of Pinter and Scott's work on the coastal terraces and uplift and folding of the islands. The sequence stratigraphy of the shelf has been interpreted north of Santa Cruz and Anacapa Islands. Sequences have been correlated from the deep basin up onto the shelf at several locations. We interpret that the tops of prograding sequences are controlled by sea level, and that the oldest of these sequences have subsided between 100 m to 200 m. At least north of Santa Cruz Island, older sequences are more tilted than younger ones. At least in the east, this subsidence is post-1 Ma, although the oldest sequence was deposited on an unconformity that had already tilted. Uplift of the islands and subsidence of the shelf is a progressive north tilt that is not consistent with the published structural model. Uplift of the islands, and probably of the Santa Monica Mountains, should be evaluated from a subsiding base-level, not from sea level.


Chris Sorlien
Marc Kamerling

2/15/97 - 8/14/98 $60,000

US Geological Survey, 1434HQ97GR03085

Fault Displacement and Fold Contraction Estimated by Unfolding of Quaternary Strata, Onshore and Offshore Ventura Basin, California

Christopher Sorlien, and Dr. Kamerling and were funded by U. S. Geological Survey National Earthquake Hazards Reduction Program (NEHRP) to study folding and faulting in the eastern Santa Barbara Channel and Ventura Basin using a three-dimensional map restoration technique. A 1 Ma horizon offshore was mapped, and this map and the published onshore map were digitized. A 3-D view was created, and the structure-contour map was unfolded and restored to an initial horizontal state. A web page was created with Carmen Alex ( ) Published and unpublished cross sections were used to create a structure contour map of an ~1.8 Ma horizon through western onshore Ventura basin. Industry seismic reflection data and well data were used to create a new structure-contour map of this horizon offshore. This map of a deeper horizon will be restored if our proposed renewal is funded. Previously, 3.5 km of post-1 Ma left slip and a similar amount of vertical motion was claimed for the Oak Ridge fault near Santa Paula based on an offset stratigraphic marker. It is not possible to restore the 1 Ma horizon with this much left slip unless an unmapped fault cuts across Ventura basin near Santa Paula. Without this fault, post-1 Ma left slip in this area is between 1 and 2 km, or half the published estimate. Another NE-SW tear fault is required by our subsurface mapping near the Ventura River, and this fault may link slip on the Red Mountain fault to slip on the Padre Juan-Javon Canyon fault. These faults may form important kinematic boundaries that could limit the rupture areas of future earthquakes. Correlation of post-160 ka horizons dated at Ocean Drilling Program site 893 and the 1 Ma horizon shows that vertical motions across the offshore Oak Ridge fault and related folds have not changed in the last 1 Ma.


Arthur Sylvester

4/1/96-3/31/98 $77,288

US Geological Survey, 1434HQ96GR02732

Strain Partitioning in Los Angeles-Ventura Region, Southern California: Evidence from Precise Leveling Across Active Folds and Faults

Ventura Avenue anticline is a geologically young, major fold that grew 4-5 mm/yr during Holocene time (Rockwell, et al. , 1988). Comparison of three first-order leveling surveys across the anticline, 1978 (NGS), 1991 (County of Ventura), 1997 (UCSB) indicate that the crest of the Ventura Avenue rose 20 mm between 1978 and 1991 and about another 10 mm between 1991 and 1997, for an annual rate of uplift of about 1.5 mm. All of this has happened without the benefit of nearby earthquakes. Between 1978 and 1991 no earthquakes > M2.0 were recorded anywhere close to the anticline, even though GPS measurements from 1988 to 1994 indicate horizontal shortening of 7 mm/yr across the entire Ventura basin. By state law, furthermore, produced fluids must be replaced to mitigate potential subsidence, and comparison of two NGS levelings done shortly after the law went into effect in 1956 indicate that a re-injection program was successful in countering local subsidence (Buchanan-Banks, et al. , 1975). The aseismic growth of Ventura anticline provides permissive evidence to counter assumptions that folds only grow coseismically in this region, and that strain accumulation inferred from GPS measurements will be released only elastically in future, frequent, Northridge-type earthquakes, or infrequent, even larger shocks (Dolan et al. , 1995). This observation of aseismic fold growth is critical to understanding how regional strain may be partitioned between elastic and anelastic deformation. If aseismic fold growth and possibly fault creep are occurring elsewhere in the greater Los Angeles area, thereby releasing some fraction of accumulated strain energy, then seismic hazard estimates for the Los Angeles region may be significantly different than inferred by Dolan et al (1995) based on a wholly elastic model. Impending earthquakes may be smaller and/or less frequent, therefore, than maintained by those investigators.

See additional information at:


Arthur Sylvester

4/1/97-3/31/99 $49,999

US Geological Survey, 1434HQ97GR03132

Investigation of Seismic and Aseismic Behavior of Active Fault Segments: Integration of UCSB Nearfield Geodetic Arrays

According to conclusions reached from recent GPS geodesy, more elastic strain energy is accumulating in the Los Angeles region than is being released by means of earthquakes, leading to the conclusion that the region may expect either more frequent Northridge 1994 size earthquakes in the future or less frequent but larger earthquakes (Dolan et al. , 1995).

One explanation for the discrepant strain budget is that a "significant" proportion of that horizontal shortening strain is being released anelastically - slowly, inexorably by fault creep, folding, and regional uplift - although some investigators (Dolan et al. , 1995) dismiss this possibility with precious little evidence.

This investigation seeks to test the hypothesis that the Transverse Ranges in southern California are rising anelastically as the partitioned response to measured north-south crustal shortening. It is a relevant phenomenon for a NEHRP study, because if a large proportion of the regional strain is being released anelastically, then less is available for elastic release in earthquakes, meaning that the earthquake hazard is not as great for the greater Los Angeles area as some investigators have maintained.

We know the Transverse Ranges rise at the time of earthquakes, and based on our leveling in 1996/97, we think the Transverse Ranges also rise in interseismic time by anelastic deformation. We think that a comparison of levelings across the ranges in 1998 when compared with previous levelings will reveal the place and rate of uplift since as early as 1934, when most of the main bench marks were installed.

We intend to resurvey two lines by precise leveling of two lines of existing bench marks across the Transverse Ranges - one along Hwy 33 from Ventura to Cuyama, and one in Cajon Pass from San Bernardino to Hesperia. We shall make simultaneous GPS observations of almost all bench marks to integrate with the greater network of GPS bench marks in southern California. These data and their subsequent analysis will link 60 years of leveling data with present and future GPS observations, and yield a 60 year record of vertical movement of two broad and different parts of the Transverse Ranges. We anticipate that we'll find the mountains have risen, then we shall model the data to understand how and why.

The importance of the test bears on balancing the strain budget in southern California - how the geodetically measured shortening is apportioned into stored elastic strain that is available for potential damaging earthquakes, and if and how much is released anelastically by creep, regional vertical uplift, and folding.


Alain Trial
Libe Washburn

7/1/96-6/30/98 $24,200

University of California Energy Institute, UCSB 08960644

Impacts of Oil Production on Natural Hydrocarbon Seepage in the Santa Barbara Channel Determined by Fluid Dynamic Modeling of Dissolved Hydrocarbon Plumes

Natural oil and gas seeps offshore of Coal Oil Point in the Santa Barbara Channel release a significant amount of hydrocarbons (in the form of gas, oil and tar) into the environment. Because the seeps are in relatively shallow water only part of the gas dissolves in the ocean while the rest is released into the atmosphere where it contributes to ozone formation. Sonar surveys by the Institute for Crustal Studies determined the size and location of the seep field and have shown that the amount of gas (primarily methane) being released into the atmosphere is 105 m3 per day. Analyses of the water during the 1995 and 1996 cruises found the peak dissolved methane concentrations of order 1000 nmol/l. In order to verify the magnitude of the gas flux, I have used the Princeton Ocean Model to simulate the water flow in the Santa Barbara Channel. The computational domain extends from shore to the channel islands and from Anacapa Island in the east to Point Conception in the west. The numerical grid consists of 105 columns by 43 rows of control volumes. There are 10 control volumes from sea surface to bottom scaled in size based on the water depth. Turbulence, realistic bathymetry, temperature and salinity variations, tidal forces, and wind stresses are included in the simulations. Dissolved hydrocarbons are represented by a passive tracer. The simulations are driven by both wind stresses (constant northwesterly wind over the entire domain) and tidal fluctuations in the water depth. The simulations produce a predominantly westward flow close to shore in agreement with available oceanographic data. In order to obtain dissolved methane concentrations consistent with our analyses, the amount of methane going into solution must be around 5 x 104 m3 per day.


Libe Washburn
Jordan Clark

7/1/97 - 6/30/99

University of California Energy Institute, UCSB 08970726

Direct Measurement of Natural Hydrocarbon Seepage Off Coal Oil Point Near Santa Barbara, CA

A significant source of air pollution for Santa Barbara County is the natural seepage of hydrocarbons off Coal Oil Point near Santa Barbara, CA. The seepage contributes to air pollution in the county because the hydrocarbons contain reactive organic gases (ROGs). ROGs are precursors in forming ozone which is a significant air pollutant for the county. The hydrocarbons seep into the water column from the sea floor as gaseous emissions and as liquid oil. We are using sonar surveys to map these bubble emissions and to quantify emission rates. We have found that the gaseous seep emissions may equal the ROGs emitted by all mobile sources in the county. The objective of this research is to measure directly the seep gas emissions to the atmosphere with a new, independent technique. It is critical to policy makers in Santa Barbara county to have accurate inventories of all sources of ROGs. This research will contribute to this by improving estimates of natural hydrocarbon seepage. It will also help policy makers evaluate the effects of offshore oil production in the Santa Barbara Channel.


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Ralph Archuleta

11/26/95 - 11/25/97 $219,022
12/20/95 - 12/19/98 $665,712

Institute for Protection and Nuclear Safety; Nuclear Regulatory Commission

4060-00000470, 4060-00001217 NRC 04-96-046

Garner Valley Downhole Seismographic Array (GVDSA) Project

The Garner Valley downhole seismographic array (GVDSA) project, installed under the U. S. Nuclear Regulatory Commission contract NRC-04-87-108 in cooperation with the French Commissariat à l'Energie Atomique (CEA), has two main scientific objectives, first; understanding the effects of the near-surface soil conditions on seismic ground motion to improve the ground motion prediction capabilities for design, seismic hazard assessment, and hazard mitigation: and second; understanding the effect of earthquake ground motion on the hydraulic conductivity of ground water systems for the deep storage of nuclear waste.

The near-surface geological site conditions have been shown to be the dominant factor in controlling the amplitude and variation of strong ground motion, and the damage patterns that result from large earthquakes. A unique set of data collected from the Garner Valley project makes it possible to advance two major areas of engineering seismology. The first problem is how weak motions scale to strong motions. The second one is how the recordings at different soil types scale to each other, especially with respect to a competent rock ("reference") site. The understanding of competing effects of amplification and attenuation (including non-linearity) is of a vital importance for seismic design studies. The site is located near the Anza segment of the seismically active San Jacinto fault, which is expected to experience a large earthquake of magnitude 6.5 or greater.

At Garner Valley we measure the ground motion during earthquakes in the bedrock, 500 and 220 meters below the surface, at 50 meters below the surface in a zone of weathered granite, and at 22, 15, and 6 meters below the surface in a layer of soft alluvium. The ground motion is also measured at the surface above these borehole instruments by 5 stations in a linear array, one of which is directly above the borehole instruments.

In the deepest borehole (500 meter), downhole pressure transducers are located within sealed off fracture zones. The effects of earthquake ground motion and the rock-mass hydraulic response to ground motion are important factors in the short- and long-term performance of a high-level nuclear waste repository. This part of the project was designed and undertaken to provide fundamental data regarding the influence of earthquake ground motion on dynamic and static changes to the pore pressure in the rock mass. In addition to the downhole pressure transducers, static and dynamic changes in the pore pressure at different levels within the bedrock borehole are also measured via tubes (sampling lines) which are connected to pressure transducers at the surface and extend into the borehole to various depths. Recent observations of dynamic pore-pressure changes from these sampling lines during small earthquakes may prove to be the first such measurements ever made in deep bedrock.

In the past year, research resulted in developing new approaches to empirical site response estimation. The idea is to study three-dimensional seismic radiation field instead of treating each component of ground shaking individually. A standard approach to estimating relative site response (Borcherdt, 1970) is to calculate the 1D transfer function between a rock and a soil sites as an average spectral ratio of individual components. We introduced a 3D transfer function between all three components of motions at two sites as a 3x3 matrix transformation. This matrix accounts for complex propagation effects such as conversions of different types of seismic waves, differences in incidence angles, etc. It can be determined from observations of at least three earthquakes at both sites. That suggests a possible explanation of some causes of an apparent event-to-event variability of standard 1D relative site response estimates as each single earthquake observation is capable of imposing only three constraints on nine a priori unknown components of the transfer matrix. When there are more than 3 observations, the transfer matrix is obtained as a maximum likelihood solution of an overdetermined system of equations. After combining two horizontal components into one complex time series we arrived at a new method of studying polarization properties of ground motion (Tumarkin and Archuleta, 1997). Our approach is different from the Takizawa's directional distribution of energy method (Takizawa, 1982; Kawase and Aki, 1990). For each frequency we are calculating the maximum amplitude and the corresponding azimuth of particle motion in the horizontal plane, as well as the eccentricity of this motion. That allows us to perform a detailed analysis of frequencies at which the ground motion is the largest and polarized the most, and how these frequencies vary from site to site. These new approaches are complementing the old ways of site response analysis and are designed for alerting to possible complex propagation effects (focusing, 3D structure, etc. ), that are important in detailed microzonation studies for critical facilities.


Ralph Archuleta

7/1/95 - 2/28/99 $122,336

University of California, Office of the President

Campus Laboratory Collaboration, UCSB 08950868

CLC Seismic Hazard Study of the University of California Campus at Santa Barbara

A multi-disciplinary seismic hazard study of the UC Santa Barbara campus is being conducted as part of a UC-LLNL Campus-Laboratory—Collaboration program. The primary objective of this project is to predict the ground motion for one critical structure on the UCSB campus based on potential seismic sources and local site conditions. Once completed, the CLC project will then provide a template to evaluate other buildings on campus, as well as provide a methodology for evaluating seismic hazards at other critical sites in California, including other UC locations at risk from large earthquakes. Another important objective of the CLC project is the education of students and other professionals in the application of this integrated, multi-disciplinary, state-of-the-art approach to the assessment of earthquake hazard. The CLC seismic hazard study will consist of four phases: Phase I — Initial Source and Site Characterization, Phase II — Drilling, Logging, Seismic Monitoring, and Laboratory Dynamic Soil Testing, Phase III — Modeling of Predicted Site-Specific Earthquake Ground Motions, and Phase IV — Calculations of 3D Building Response. Phase I has been completed and Phase II is nearly finished.

To date, the CLC study includes GIS-based mapping of active faults and folds, CPT soil studies, shallow P- and S-wave seismic refraction surveys, in-situ downhole velocity measurements and array monitoring of local seismicity. The UCSB campus sits on a raised marine terrace caught between the blind, north-dipping North Channel fault and the steeply south-dipping More Ranch fault. Uplift rates based on a dated marine coral are about 1 mm/yr, although these faults also likely include a significant strike-slip component. Over much of the UCSB campus, approximately 5 m of dry Quaternary terrace deposits (Vp ~350-500 m/s; Vs ~200 m/s) overlie low-density saturated Sisquoc Formation (Vp ~1500 m/s; Vs ~400-500 m/s). The campus is also situated above a sedimentary syncline. Amplification effects due to focusing from the syncline and the near-surface low velocities may represent a significant hazard to the campus. As part of Phase II, two 75-m boreholes were drilled this spring to provide additional information on subsurface material properties and to install uphole/downhole instruments to record strong and weak ground motion. Earthquakes of magnitude 4.9 and 3.2 at distances of 300 and 150 km, respectively, have been recorded by the new instrumentation. The data are provided real-time to the SCEC data center at Caltech. The uphole and downhole data will be used to provide empirical estimates of local site effects, to calibrate theoretical models of site response, and to predict future ground motion for use in modeling the 3-D response of various buildings on the UCSB campus.


Ralph Archuleta

10/1/97-9/30/98 $24,395
1/15/98-12/31/99 $89,440

Lawrence Livermore National Laboratory; National Science Foundation

IGPP 98-GS012 EAR 97-25709

Dynamic Earthquake Rupture Simulation on Dipping Faults

David Oglesby in collaboration with Ralph Archuleta and Stefan Nielsen, has centered on investigating the effect that geometry has on the dynamics of dip-slip earthquake faults. Due to the asymmetric geometry of dipping faults, dynamic simulations of earthquakes on such faults produce asymmetric ground motion near the fault. The ground motion from a thrust/reverse fault is larger than that of a normal fault by a factor of two or more, given identical initial stress magnitudes. The motion of the hanging wall is larger than that of the footwall in both thrust/reverse and normal earthquakes. The asymmetry between normal and thrust/reverse faults results from time-dependent normal stress caused by the interaction of the earthquake-generated stress field with the earth’s free surface. The asymmetry between hanging wall and footwall results from the asymmetric mass and geometry on the two sides of the fault. Both the hanging wall vs. footwall effect and the thrust vs. normal fault effect are maximum for a fault that intercepts the free surface, and decay rapidly with depth of fault burial. Oglesby is currently performing preliminary simulations of thrust faults that change dip with depth.


Ralph Archuleta

4/1/91 - 1/31/98 $2,470,491

University of Southern California

Southern California Earthquake Center, USC 572726

See individual research summaries below for projects included in this grant.


Ralph Archuleta

4/1/91 - 1/31/98

University of Southern California

Southern California Earthquake Center, USC 572726

The Portable Broadband Instrument Center (PBIC)
Southern California Earthquake Center (SCEC)

The Portable Broadband Instrument Center (PBIC) provides seismic instrumentation to SCEC investigators for specialized Center research in southern California. Having control of instruments allows for rapid redeployment of the equipment in the event of a significant southern California earthquake. Past aftershock deployments have used PBIC equipment to supplement Southern California Seismic Network (SCSN) coverage and to obtain digital records at existing strong ground motion sites. PBIC instrumentation is compatible with Incorporated Research Institutes for Seismology (IRIS) PASSCAL equipment and has been used in several cooperative projects. In addition, the PBIC develops calibration and other quality control methods for use with the recording equipment and performs routine maintenance and repairs on seismic instrumentation for other SCEC institutions.

The vast majority of the PBIC equipment was used the entire year. The seismic hazard assessment phase of the Campus Laboratory Collaborative (CLC) project finished in early March freeing up the equipment for the Los Angeles Basin Passive Seismic Experiment (LABPSE) run out of UCLA by Dr. Monica Kohler. This experiment, consisting of eighteen seismic stations distributed from Seal Beach to the base of the San Gabriel Canyon, collected data to supplement the active source data collected by the LARSE project in late 1994.

Dr. Jamison Steidl of the Institute for Crustal Studies (UCSB) began his portable borehole study in January 1998. This study will investigate site responses using earthquake data recorded from sensors installed in 100m boreholes at several sites in the Los Angeles Basin.

The PBIC instruments were used by Javier Favella of Caltech to acquire data for a project that involved shaking the Millikan library, on the Caltech campus, with a large mechanical shaker mounted to the roof of the building.

Outreach programs continue to play an important role in the PBIC. Development of the PBIC World Wide Web (WWW) page has continued this past year including the addition of a java applet for calculating data collection rates and expanded vendor and equipment information. ICS researchers and the PBIC participated in seismological demonstrations at several local schools, including Isla Vista Elementary, Adams Elementary and La Colina Jr. High.


Ralph Archuleta

4/1/91 - 1/31/98

University of Southern California

Southern California Earthquake Center, USC 572726

Strong Motion DataBase

The UCSB Strong Motion DataBase (SMDB) is a relational database containing parametric information about 5,559 accelerograms, 121 earthquakes, and 654 strong motion stations, all of the data recorded within the state of California. Users can query the database directly from the World Wide Web ( and download the strong motion data from an on-site FTP server, or, whenever possible, from outside FTP sites, such as the U. S. Geological Survey and the California Strong Motion Instrumentation Program sites.

Some of the parametric information in the database include peak ground acceleration, epicentral distance, hypocentral distance, closest distance to the fault, response spectral amplitudes at 0.3, 1.0, and 3.0 seconds, instrument trigger times, earthquake locations, magnitudes, and focal mechanisms, station locations and site geology, and selected references.

Six access methods have been developed and can be found on the home page. Station and event summaries allow the user to view summaries of all of the data which is available for a particular station or earthquake. Users can also query the database through two HTML forms pages, a basic search page and a custom search page. These pages allow the user to search on all of the parametric information in the database. An interactive Java map applet has also been written that allows the user to easily search for earthquakes and stations in particular locations. Finally, for those users familiar with the database query language, SQL, a search page is available that allows the user to input a SQL query directly. The data returned by any of the above access methods can be downloaded directly from the search results.

The database is currently being served on a Sun Ultra 10 computer with a 300 MHz UltraSPARC processor, 17 GB of disk space, and 640 MB of RAM. The database software is the latest version of Oracle8 and includes the Oracle Web Application Server. A dedicated ethernet line is connected to a single port on a 10Base-T ethernet switch that is connected directly to the UCSB campus FDDI backbone.


Ralph Archuleta
Kim Olsen

3/1/97 - 2/28/99 $55,000

US Geological Survey, 1434HQ97GR03100

Three-Dimensional Ground Motion Modeling in the San Francisco Bay Area

During January and February 1998, Dr. Paul Spudich spent a month at ICS working with Ralph Archuleta, graduate student Eleanore Jewel and Kim Olsen on 3D ground motion calculations for the San Francisco Bay area. They received and visualized the recently developed 3D crustal model of the bay area from USGS. The 1979 Coyote Lake earthquake was simulated in 1D and 3D models and the ground motions were compared to those from other studies. They developed 2.5D models of the Calaveras fault zone in order to study the radiation pattern and waves trapped in the fault zone. Finally, a study has been initiated to examine the effects of 3D crustal structure on kinematic slip inversion.



Ralph Archuleta
Alexei Tumarkin

9/1/97 - 6/30/98 $62,000

University of Southern California,

Southern California Earthquake Center, PO 030905

Integrated Approach to Ground Motion Prediction

The work on this SCEC project related to ground motion prediction led to formulation of this problem in terms of two global characteristics of the scenario earthquake -- seismic moment and radiated energy. The radiated energy is one of the two most important observational characteristics of the earthquake process. While the seismic moment constrains the level of radiation at the lowest frequencies, the energy is determined by the total spectral power. With the recent advances in compiling energy estimates for major earthquakes it is now possible to examine whether state-of-the-art models of earthquake sources produce realistic values of both the seismic moment and the radiated energy. For this purpose we use an estimate of the radiated energy for general models of extended earthquake sources based on the knowledge of the slip-rate history on the fault (Rudnicki and Freund, 1981). Kim Olsen and Alexei Tumarkin calculated the radiated energy for three-dimensional dynamic fault models that include a length scale. The resulting total moment rate functions can be described by a simple shape. Moreover, the average stress drops were almost four times larger than the apparent stresses, suggesting that the average radiational friction is of the same magnitude as the apparent stress. Tumarkin also studied the energy and apparent stress parameters as a function of the rise time and rupture velocity for kinematic models. The addition of the energy parameter allowed them to constrain the range of predictions thus reducing the uncertainty of the results. A talk was given at the SSA Annual Meeting (April 1998, Boulder, CO) and an abstract submitted for the 1998 Fall AGU meeting.


Ed Keller


University of Southern California

Southern California Earthquake Center, USC 572726

Earthquake Hazard of the Santa Barbara Fold Belt, California

The major accomplishment in this project (1997-98) has been to develop a new method of correlating uplifted marine platforms based upon analyses of oxygen isotopes from marine fossils collected at the interface between the bedrock, wave-cut platform and overlying sediments. The method we are developing will allow for correlation of terraces that have been deformed by uplift, faulting, or folding, as well as those dismembered by erosional processes. The method will then allow for rates of uplift to be calculated for marine platforms that are correlated to other platforms of known numerical ages.


Ed Keller

12/1/96 - 11/30/98 $76,091

US Geological Survey, 1434HQ97GR02978

Earthquake Hazard of the Santa Barbara Fold Belt, California

During the 1997-98 academic year, work on the project has identified the major potential seismic sources in the Santa Barbara Fold Belt. We have also completed our work to evaluate the Arroyo Parida Segment of the Mission Ridge Fault System. Our work is demonstrating the process of lateral propagation of prominent folds in the Santa Barbara Fold Belt including Mission Ridge and the newly identified Rincon Creek Anticline. Finally, rates of uplift have been calculated based upon mapping of shoreline angles of late Pleistocene marine platforms.



Grant Lindley

8/5/94 - 8/4/97 $213,370

Nuclear Regulatory Commission, NRC 04-94-079

Analysis of Source Spectra, Attenuation, and Site Effects Using Broad Band Digital Recordings from the U. S. Seismograph from Central and Eastern United States Earthquakes

A three-year project to conduct investigations of central and eastern United States earthquakes has recently been completed. The purpose of this project has been to improve our ability to predict ground motions in the central and eastern United States from future earthquakes. This project collected and analyzed data from the United States National Seismograph Network (USNSN); this data set included data from 207 earthquakes that occurred over a five-year period in the central and eastern United States and southeastern Canada. A total of 347 recordings were included in the analysis from 25 stations.

Several separate studies were conducted for the project. The most recently completed study compared the results of 200 source parameter measurements from 27 previous studies of eastern North American earthquakes. These studies were combined to test how the ground motions measured at the earth’s surface scale with increasing earthquake magnitude. One of the important parameters that measures the strength of an earthquake is the stress drop, which measures the drop in stress along an earthquake fault that occurs during an earthquake. This stress drop is often assumed to be roughly a constant, independent of the earthquake size. By combining the results from the 27 previous source parameter studies, it was found that these results are inconsistent with a constant earthquake stress drop for eastern North American earthquakes.

A second study completed for this project in the last year examined the attenuation of seismic waves and site responses of USNSN stations by analyzing the recordings of the regional earthquake phase, Lg . Generally, the ground motion recorded from an earthquake can be broken down into three components: the source effect, the path effect (including attenuation), and the site effect. The prediction of ground motion from an earthquake is often made easier and more reliable by estimating each of these three effects separately. The second study involved a combined analysis of data from various sources, paths, and station locations, in order to separate the three effects.

For the purposes of the study, the data were divided into five regions: the northeastern United States, the central United States, the southeastern United States, California and Nevada, and the Basin and Range province. Among the results of this study, large differences were found in the attenuation of the Lg phase between the western United States and the central and eastern United States. These differences are likely related to the rate of tectonic activity that occurs in the different regions.



Kim Olsen

2/3/97 - 9/30/99 $67,000

Los Alamos National Laboratory, F42200017-3Z

Modeling Non-Linear Ground Motion in the LA Basin

Dr. Eric Jones, Los Alamos National Laboratories, and Dr. Kim Olsen have developed a hybrid method to model non-linear soil amplification using finite-fault ground motion. They computed the source-time functions at a datum plane below the area of interest using a 3-D elastic finite-difference method. The source-time functions were then propagated up to the surface through a 1D soil column using a full non-linear method. The method has been tested on selected sites from the San Fernando Valley (JFP and SSA). The results are similar to those obtained from ratios of weak and strong motion recordings from the Northridge earthquake.


Kim Olsen

2/1/97 - 1/31/99

University of Southern California

Southern California Earthquake Center, USC 572726

Three-Dimensional Elastic Finite-Difference Simulation of a Dynamic Rupture

In collaboration with Professor Raul Madariaga and Ralph Archuleta, Kim Olsen has developed a computer method to model an earthquake including a complex variation of the friction on the fault plane. They have used the method to simulate the 1992 M 7.3 Landers earthquake as the propagation of a spontaneous rupture. The simulation used an initial stress distribution on the fault calculated from fault movements derived in a prior study. The simulation shows the rupture propagating on the fault along a complex path with highly variable speed and pulse width. The results have implications for the state of stress on the fault following an earthquake as well as the seismic waves radiated during the earthquake, and the method may provide the framework to estimate earthquake rupture parameters from recorded seismograms in the future. In collaboration with post-doc Stefan Nielsen, Kim Olsen has improved the numerical accuracy of the 3-D dynamic modeling.


Kim Olsen

8/15/96 - 7/31/99 $120,000

National Science Foundation, EAR 96-28682

Ground Motion Modeling in Los Angeles

Kim Olsen has carried out a study on ground motion amplification for the Santa Monica area with SCEC summer intern Carmen Alex. They examined whether amplification due to a proposed buried lens-shaped basin boundary could account for the anomalously large amplification observed in the area during the Northridge earthquake. The results suggested that the "lens-effect" could only account for less than 50% of the observed amplification. Currently, Olsen is working on extending the amplification study for Santa Monica to a 3D model.

Researchers from SCEC are currently trying to finish the "phase 3" project. Olsen is responsible for mapping the long-period amplification from the 3D Los Angeles basin. He has found a strong variation in amplification pattern and magnitude for nine different scenario earthquakes, with the largest amplification occurring above the deepest part of the basin. Sensitivity tests show that anelastic attenuation can significantly reduce the ground motion for frequencies below 0.4 hz, and that a randomized slip distribution on the fault generates ground motions similar to those for a smooth slip distribution.



Jamison Steidl

2/1/97 — 1/31/99

University of Southern California

Southern California Earthquake Center, USC 572726

Site Response: Completion of Phase III and Beyond

The past year’s efforts under this project have been focused on the completion of the SCEC Phase III report. Response spectral amplification factors from weak-motion data, strong-motion data, and analytical models, are examined to find a correlation between these factors and geotechnical site parameters. In other words, can we better predict ground motion (reduce the residuals to the attenuation relations) given more detailed geotechnical and geological information regarding the local site conditions? The underlying motivation being that if we can better predict the ground motion then we can do a better job in the seismic hazard calculation by including the site response. This multi-disciplinary approach has been useful in determining where improvements to our models can be made and what new measurements are needed.

Site response factors are determined for strong motion sites in Southern California by comparison of observed response spectral acceleration (RSA) to predicted rock RSA. The site response is calculated using a rock attenuation relation as the "reference" motion to produce factors that can be used to include site response in probabilistic seismic hazard analysis (PSHA). Strong motion records from 1933 through 1994, provided by many agencies to the Southern California Earthquake Center's (SCEC) strong motion database (SMDB), are used as the data. Site response factors are calculated at four periods; 0.1, 0.3, 1.0, and 3.0 seconds. These factors are averaged according to surface geology and predicted input peak ground acceleration (PGA). Correlation with weak motion site response, surface geology, and near-surface shear wave velocity is examined. There is a trend towards larger site response factors with younger geology. At short periods (0.1 & 0.3) on Quaternary geology, there is a decrease in the site response factors at high levels of input motion which suggests nonlinear soil behavior. Independent weak-motion site effect studies are found to produce similar results, and the weak-motion site response is found to be consistent with the low-input strong motion site response.

In addition to the above work, we began a new study to look at the correlation between theoretical site response and empirical estimates of site response. The theoretical estimates are based on numerical simulation of wave propagation using the measured wave velocity in the near surface. The empirical site response estimates are determined using borehole-surface sensor pairs at the same sites where the wave velocity is measured. The study focuses on the Van Norman Dam Complex where very large and variable ground motion was recorded during the 1994 Northridge earthquake. With the help of a SCEC undergraduate summer intern we are currently in the empirical data collection phase, and judging from the earthquakes recorded to date, the project should produce some very useful results.


Jamison Steidl
Ralph Archuleta

2/1/97 — 1/31/99

University of Southern California

Southern California Earthquake Center, USC 572726

SCEC Borehole Instrumentation Initiative

The variability of observed ground motion and damage patterns over short distances produces a large degree of uncertainty in our ability to predict shaking from future earthquakes. Part of the variability is caused by the local near-surface site conditions. Installing borehole instrumentation below the surface soil layers allows us to remove the near-surface site effect at a few select stations. These borehole stations produce data that has not been distorted by the effect of the surface materials. This will allow for direct estimation of site effects and provide a test for the calibration and improvement of physical models of soil response. It will also give us a much clearer picture of the incident ground motion, which can be used to study the earthquake source process and the regional crustal structure in more detail. In addition the borehole data can be used as empirical Green's functions (the input motion) for predicting ground shaking at surface sites in the region surrounding the borehole station.

This marks the second year of the SCEC borehole instrumentation initiative. The long-term objective of this project is to instrument three borehole sites per year in the Los Angeles region. Currently five sites have been selected and are now in the final stages of completion. All five of the sites have been drilled, logged for wave velocity, and cased for deployment of the downhole instrumentation package. Data from one of the stations is already being provided in real-time to the Caltech/USGS Southern California Seismic Network (SCSN) and is being stored online at the SCEC data center. The other four stations should be online by the end of 1998.

Hazardous Waste:

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Stephen Cullen
Lorne Everett

3/8/96-9/30/97     $30,000

Lawrence Livermore National Laboratory, B291841

California Leaking Underground Fuel Tank (LUFT) Site Data Analysis

ICS Researchers Dr. Stephen J. Cullen, Dr. Lorne G. Everett, and Dr. Joel Michaelsen were contracted by the California State Water Resources Control Board to conduct additional analysis of data derived as a part of a previous study which resulted in the report entitled California Leaking Underground Fuel Tank (LUFT) Historical Case Analysis in which ICS researchers Cullen, Everett, and Michaelsen had played a key role.

A major outcome of the above-cited effort was the creation and maintenance of a significant database consisting of hydrogeologic data drawn from LUFT sites throughout the state. Previous data analyses conducted by the ICS researchers had employed a variety of statistical techniques to characterize the setting and character of LUFT sites as they occur throughout the state. Key contaminant hydrogeologic characteristics such as benzene concentration distribution, plume size, depth to groundwater, and an analysis of the effectiveness of various applied remediation techniques were evaluated. The temporal and spatial coverage of sites in a data set of this size afforded an opportunity to conduct an additional statistical analyses of the data set for the purpose of understanding the distribution and fate of petroleum hydrocarbons in the subsurface. The analysis undertaken focused on benzene as representative of a highly mobile and toxic petroleum hydrocarbon compound. This investigation evaluated the factors that characterize the occurrence, distribution, and fate of benzene at a variety of locations in California where groundwater has been impacted by a LUFT(s).

One of the major conclusions of the previous study was that with rare exceptions, a petroleum hydrocarbon release will naturally degrade in California’s subsurface environments and that passive bioremediation can be as effective as active engineered remediation approaches. In this study, Cullen, Everett, and Michaelsen drew upon that database, and the knowledge learned from the previous data analyses, to perform additional analyses in an attempt to shed light on the cause and effect relationships which underlie the findings of the previous study. Further analyses were also performed to confirm the findings of the previous work. . A technical report and peer reviewed paper is expected to be published which articulates the methodologies and findings of the study.


Stephen Cullen
Lorne Everett

10/1/96-9/30/98     $43,500

Lawrence Livermore National Laboratory, B333265

Petroleum Hydrocarbon Demonstration Project

In June 1994, the State Water Resource Control Board (SWRCB) contracted with a consortium of campuses of the University of California to study the cleanup of Leaking Underground Fuel Tanks (LUFT) in California. ICS Researchers Dr. Stephen J. Cullen, Dr. Lorne G. Everett, and Dr. Joel Michaelsen played key roles on the consortium team. The study consisted of data collection and analysis from LUFT cases throughout the state and a review of other studies on LUFT cleanups. Two final reports were submitted to the SWRCB in October and November of 1995. The reports were entitled: Recommendations To Improve the Cleanup Process for California’s Leaking Underground Fuel Tanks (LUFTs) and California Leaking Underground Fuel Tank (LUFT) Historical Case Analysis .

One of the important recommendation of this study was to identify a series of LUFT demonstration sites and to form a panel of experts made up of scientific professionals from universities, private industry, and Federal and State regulatory agencies. This panel would evaluate and interpret data from LUFT demonstrations sites for the purpose of applying the recommendations derived from the previous studies mentioned above. Again, ICS researchers Dr. Stephen J. Cullen and Dr. Lorne G. Everett, because of the experience and demonstrated knowledge of the field, were invited to participate on the expert panel.

Sites selected for inclusion in the study were:

    • Army Presidio at San Francisco
    • Barstow Marine Corps Logistic Center
    • Camp Pendleton Marine Corps Base
    • Castle Air Force Base
    • El Toro Marine Corps Air Station
    • George Air Force Base
    • China Lake Naval Weapons Center
    • Travis Air Force Base
    • Vandenberg Air Force Base
The project consisted of meeting with site staff, regulators, and expert panel liaisons to discuss and develop a site conceptual model and to identify site contaminant migration pathways and environmental receptors of concern. A site visit was made to each demonstration site to view the site physical layout and to identify gaps in the site hydrogeologic database. The expert panel then analyzed and evaluated the data to determine the potential for natural attenuation mechanisms to exist at the site and to determine the applicability of implementing a remediation approach which relies on intrinsic remediation at the site. Further, at each site, the panel evaluated contaminant sources, pathways, and receptors and subsequently developed an appropriate risk management strategy.

Based on the results of the findings at the nine demonstration sites, the expert panel then evaluated the results of the investigations and demonstrations across the combined sites. The findings indicated that the general recommendations and conclusions derived from the 1995 reports cited above could be successfully applied and used to develop effective remediation strategies at specific sites throughout the state of California.


Lorne Everett

03/15/95-09/30/97     $75,000

US Navy, IPA A95002

United States Navy National Test Site Fuel

Hydrocarbon Remediation Program

Lorne G. Everett participated as a member of the United States Navy Science Advisory Panel in support of the Navy National Test Site Program. The program focuses on developing hydrocarbon remediation technologies that will be used by the United States Navy throughout the world. Contributions from the Vadose Zone Monitoring Laboratory focused on selecting monitoring strategies to optimize the remediation activity. Remediation technologies such as heap biopile programs, hot air vapor extraction, and the German UVB recycling system were demonstrated.


Lorne Everett

9/21/97-12/30/98 $15,996

Lawrence Livermore National Laboratory, B339044

Initiative to Improve VOC Cleanup Process by Using Historical Case Analysis

There are currently several national initiatives to reevaluate the volatile organic compound (VOC) cleanup process. The VOC initiative proposes to do an historical case evaluation that uses a large number of cases which can identify VOC release conditions that pose low risks that can be managed with minimal effort and cost versus release conditions that pose higher risks and warrant the large expenditure of money often applied to all VOC releases. Dr. Everett participated in a national consortium made up of agencies including the EPA, Department of Energy, Department of Defense which was actively involved in evaluating 400 chlorinated volatile organic compound (CVOC) sites across America.


Hugo Loaiciga

2/1/97 - 8/15/97     $51,178

Bechtel Nevada, PO 13440

Current Practice of Environmental Characterization and Monitoring Technologies

The goal of this project is to document current practices of environmental technologies in the areas of site characterization and in situ remediation process monitoring. In a six month work period, we (1) collected, assessed, and compiled information from technology users and purchasers in DOE environmental management programs and (2) produced a draft document for review by technology users, purchasers, and project sponsors.

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