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| Crustal Materials | Crustal Structure and Tectonics | Earthquakes | Hazardous Waste |
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Cathy Busby National Science Foundation EAR-9304130 8/1/93 - 12/31/96 $180,000 Facies Modeling and Process Volcanological Studies in an Oceanic Arc Terrane The Cretaceous Alisitos Group in Baja California is ideal for studies of oceanic island arc processes and products because the terrane is aerally extensive, well preserved and superbly exposed. Our detailed mapping in this terrane reveals a two-part stratigraphy: Phase I, silicic to intermediate explosive and lesser effusive volcanic rocks, and Phase II, mafic effusive and hydroclastic rocks, and associated dike swarms. Phase I rocks are best characterized as an island arc stratovolcano complex in an extensional tectonic setting with high rates of arc subsidence. This stratovolcano complex was emergent (subaerial) at its main eruptive center, and was flanked by marine basins to the present-day north and south. The southern marine basin is a volcano-bounded basin, where strata accumulated in the low areas between constructive volcanic centers, in shallow water to deepwater environments. The northern marine basin, in contrast, was downthrown into deep water relative to the main subaerial eruptive center, along a regional fault zone that (1) controlled the siting of the stratovolcano and (2) formed a boundary of an 8 km wide subaerial caldera that formed at the summit of the stratovolcano. This caldera formed during the cataclysmic eruption of a rheomorphic ignimbrite, the tuff of Aguajito. During this eruption, a debris avalanche was shed from the area of the fault zone into the downthrown deepwater basin. This deepwater debris avalanche deposit contains abundant blocks up to 100m in size, including blocks of ultrawelded tuff that were still very hot and plastic after deposition in the debris avalanche. The debris avalanche ran out at least 10 km (full extent not yet mapped), leaving a 100m thick deposit estimated at a volume of at least 8 km3. Phase II rocks record unsuccessful rifting of the island arc, recorded by widespread diking and bimodal (dacite-basalt) volcanism. Dacites occur largely as welded and nonwelded pyroclastic flow deposits. On the subaerial part of the edifice, the outpouring of basalt resulted in burial of previous topography to form a plateau of "layer cake" lava flows. In the marine realm, the lavas are commonly fragmented into hydroclastic breccias, and many of the basalt lavas/hydroclastic breccias invaded the wet sediment pile, rather than erupting onto the surface. Stanley Cisowski Texas A & M 155-20842B 07/20/94 - 2/27/97 $20,551
Paleomagnetic Investigation of Leg 155 Samples Under the Texas A&M ODP grant Cisowski has been measuring the magnetization of samples which have recorded several periods of anomalous behavior of the earth's magnetic field. One of these "excursions" of the field was first detected in a study of the paleolithic fire hearths from Australia, dating to about 30,000 bp. The extremely high sedimentation rates of the Amazon River fan deposits that he is studying are giving extremely detailed records of this and other geomagnetic excursions which have occurred over the past 100,000 years. ODP studies have also produced a detailed record of the fluctuations in the intensity of the geomagnetic field over the past 40,000 years. This intensity record can be used to determine the age of the Amazon fan sediments, and will aid in deciphering the climatic and botanical history of the Amazon basin since the last glacial period. John Crowell Professor Emeritus
Pre-Cenozoic Ice Ages and the Causes of Climate Variations Dr. Crowell has completed his memoir on the history of glaciation throughout 3 billion years of earth history. His opus is entitled: Pre-Cenozoic Ice Ages and the Causes of Climate Variations, and will hopefully be published in about a year after review and preparation for the printer. He concludes that since late-mid Archean time there has always been ice somewhere on Earth, but mainly confined to high mountains and polar regions. From time to time, especially during 9 or 10 episodes of cool climate, ice tongues have expanded to make large ice sheets that have reached the sea, including one or two episodes when these tongues allowed icebergs to drop rocky debris to the sea floor in low latitude regions. His emphasis is upon the geological record as preserved in strata. He has now completed his service as Chair of the Geology Section of the National Academy of Sciences. He plans to continue interest in the tectonics of southern California, and hope to wind up several unfinished tectonic projects. Phil Gans and Wendy Bohrson National Science Foundation EAR-9506687 9/1/95 -8/31/97 $20,072
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. 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. 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 will help decipher the role of crustal contamination in generating the variable signatures of this suite of volcanic deposits. 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. http://www.geol.ucsb.edu/~gans/eld.html
Jeff Lee National Science Foundation EAR-9526016 6/1/95 - 6/30/98 $62,356 Quaternary evolution of the Eastern California Shear Zone Between Latitudes 36 Degrees and 39 Degrees Geologic mapping at 1:6,000 scale was completed along the White Mountains fault zone and is nearly complete along the Towne Pass fault. Several tephra samples from the White Mountains fault zone and the Towne Pass fault have been irradiated for Ar/Ar geochronology; these analyses should be completed within the next two weeks. Detailed topographic profiles, using a Leica Total Station, were surveyed across the most recent fault scarp developed along the Deep Springs fault. 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 and Phil Gans National Science Foundation EAR-9526861 4/1/96 - 3/31/98 $152,383
Geometry and Timing of Gneiss Dome Formation, Southern Tibet, China This a collaborative project with a group of Chinese geologists from the Institute of Geology, State Seismological Bureau, Beijing. Our first, and quite successful, two month field season was completed Spring, 1997. We completed 1:50,000 scale mapping and detailed structural and kinematic analyses within the Kangmar dome, southern Tibet. These studies identified two primary deformation events - (1) north-south compression resulting in tight to isoclinal folds and superimposed on that (2) north-south extension resulting a domed penetrative foliation and north-south stretching lineation. Numerous rock samples were collected for petrology, microscopic structural and kinematic analyses, U/Pb geochronology, and Ar/Ar and fission track thermochronology. Work over the next year will concentrate on mineral separation for the various geochronology and thermochronology analyses, compiling structural and field data, and preparing for our second field season next year. Bruce Luyendyk National Science Foundation OPP-9316712 7/15/94 - 6/30/98 $175,536
Collaborative Research: Glacial Marine Stratigraphy in the Eastern Ross Sea and Western Marie Byrd Land, and Shallow Structure of the West Antarctic Rift Bruce Luyendyk, Chris Sorlien, Doug Wilson, Geoff, Ely, Carmen Alex, Kirsten Zellmer, Nathan Warmerdam, Ron Meyer. This is a collaborative project between Bruce Luyendyk at UCSB and Louis Bartek at the University of Alabama. We conducted a MG&G study of the Cenozoic glacial and tectonic history of western Marie Byrd Land (MBL), 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 '96 national meetings of the Geological Society of America and the American Geophysical Union (Bartek et al;, 1996; Luyendyk et al., 1996). Examination of NBP-9601 seismic and Multibeam data reveals tectonic activity and glacial erosion of the shelf in the area offshore of the Kiel Glacier on the west side of Edward VII Peninsula. The inner shelf in the Marie Byrd Land region has been stripped of sediment by glacial erosion and much of this sediment has been deposited near the shelf edge. Core samples indicate that a very different mode of glacial marine deposition is occurring in the inner shelf basins of western Marie Byrd Land as compared to other regions of Antarctica. Geophysical data map half grabens in the continental shelf of the eastern Ross Sea adjacent to Edward VII Peninsula, and in Sulzberger Bay offshore from the southern Ford Ranges. A 1000 meter high fault scarp trending NNW mapped on the east side of the Colbeck Trough, defines the west side of Edward VII Peninsula and apparently routes the flow of the Kiel Glacier into the trough. The Colbeck Trough is bare of sediments near the Peninsula but farther offshore tills apparently bury or fill it. This structure is one of the most prominent features of the eastern rift shoulder found so far. Farther east offshore from the Ford Ranges, Sulzberger and Saunders Basin are fault-controlled structures that also may have been conduits for glaciers during previous glacial maxima. These faults have down-to-the-east displacement. Therefore, the gross structure of the Edward VII Peninsula is a horst. Our ties to seismic lines farther west in the Ross Sea have identified known prominent glacial units in the Colbeck Trough region. We traced a late Oligocene unit here that is minimally disrupted by faulting in the Colbeck Trough; therefore, faulting here is largely pre-Ross Sea glaciation. During Palmer 9601 we completed a site survey for the Cape Roberts Drilling Project. A N-S trough separating Roberts Ridge and the coast is defined by west-tilted fault blocks and reflections interpreted to be from low-angle faults. The prominent north-south trending trough west of the Roberts Ridge, apparently formed as a result of localized rift basin subsidence. Based on preliminary interpretation, block tilting ceased or decreased during early Tertiary. The basin is bounded to the west by over 750 meters of vertical offset, interpreted as an intrusive granitic body, probably Cambrian to Ordovician in age. Besides this indication of east-west extension, we have also mapped NE-SW trending high angle normal and reverse faults (in places up on the east by at least 100 msec) near the drill site, that appear to cut the sea floor. We have been conducting detailed stacking and interval velocity analyses that will revise deeper the depth estimates made previously for the unconformities in the sedimentary section here. A correlation with basin-wide seismic sequences from other geophysical surveys conducted in the Victoria Land basin, indicates that units seismic units V3-V5 rise to the sea floor along the eastern bathymetric high of Roberts Ridge. V3 and V4 gently dip and thicken towards the east. Unit V4 onlaps the steeply east-dipping top reflector of V5, thought to be Late Cretaceous to Paleogene in age. V5 can also be identified by its unusually high velocity ranging from 4.0-5.7 km/s. The angular unconformity between V4 and V5 may represent the transition from the main phases of uplift of the Transantarctic Mountains to a period dominated by glaciation. http://www.crustal.ucsb.edu/antarctica/
Bruce Luyendyk UC Energy Institute UCSB 08960643 7/1/96 - 6/30/98 $23,500
Geophysical Investigation to Determine Impacts of Oil Production on Natural Hydrocarbon Seepage in the Santa Barbara Channel During the second week of August we (Bruce Luyendyk, Derek Quigley, Erik Bartsch) conducted a survey that included 2 days of 3.5 kHz sonar profiling along with 3 days of oceanographic sampling. We had two objectives: 1) to track dissolved hydrocarbons emitted from the seeps; and 2), repeat sonar measurements of seep intensity to study time-variations in seepage. An on-bottom SF6 tracer source was lowered to the sea floor in the seep field at the start of the survey. An acoustic Doppler current profiler was also installed on the seafloor to measure currents during the survey. The emission of the SF6 tracer and ambient hydrocarbon concentrations were measured and mapped with an on-board Gas Chromatograph and tracked for 3 days. Vertical sections of Conductivity-Temperature-Depth were obtained at the end of the tracking plume period. The sonar survey duplicated tracks we made on earlier surveys in 1995. An experiment was conducted in November to calibrate the 3.5 kHz system utilized for imaging gas seep bubble plumes. We sought to establish an empirical relation for a variety of bubble sizes and gas flux from an artificial source and the amplitude of the sonar return. The purpose is to estimate the gas flux from the natural seeps using our digital sonar data. The experiment was undertaken off of San Pedro, California at 120 foot water depth. A bubble release device was suspended 5 feet above the seafloor and the bubble size and flow rate were varied. Repeated passes over the bubble release device were made with the 3.5 kHz sonar towfish. Data were collected using an analog thermal recorder and also digitally at 10 kHz. The experiment was partly successful; a direct logarithmic relation was found between sonar signal and flow rate. However, we believe the source was too small and was not fully detected by the sonar on several passes. Volume flux emission estimates from the 3.5 kHz data will be compared to estimates based on a previous calibration of 50 kHz sonar data to determine if the total emissions estimated using the two different sonar systems are similar in magnitude. We are also continuing to process survey data to extend the time coverage and allow a better understanding of the evolution of seep distribution and discharge over time. We estimated the dissolution rate of methane gas from the entire seep field into a 10 m layer of the water column centered at 32 m depth to be about 4 x 105 ft3/day. This suggests that approximately 50% of the seep gas injected into the ocean at the sea floor dissolves during its travel through the 60 meter deep water column. The flux of dissolved hydrocarbons to the atmosphere downstream of the seeps due to gas exchange across the air- water interface is small (less than 5% of the bubble flux above the seeps) because the water column is highly stratified and little mixing occurs between depths. We also have completed a high resolution isopach map of the Quaternary overburden in the Coal Oil Point seeps study area. We found that a great portion of the seep field is not coated by a thick layer of pelagic and terrigenous sediment, but rather by less than a meter of apparently unconsolidated overburden above siliceous shale of the Sisquoc formation. We have arranged for a side scan sonar survey of the study area that will yield a high resolution map-view image of the sea floor. The side scan sonar map will help us understand the structural geological characteristics of the hydrocarbon seeps field. http://www.crustal.ucsb.edu/seeps/
William McClelland and Brian Patrick National Science Foundation OPP-9423534 07/01/95-06/30/97 $131,452 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 and Marc J. Kamerling US Geological Survey 1434HQ97GR0314 4/17/97-4/16/98 $118,680
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 have been 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 3-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. Step 1 is now complete and Step 2 is underway. The maps and cross sections will be digitally scanned and converted to JPEG images. The digital images will be available to the public from our website at http://www.crustal.ucsb.edu. Higher resolution versions will be 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. http://www.crustal.ucsb.edu/hopps/
Chris Sorlien and Marc Kamerling US Geological Survey 1434HQ97GR03085 2/15/97 - 2/14/98 $60,000
Fault Displacement and Fold Contraction Estimated By Unfolding of Quaternary Strata, Onshore and Offshore Ventura Basin, California The goal of this project is to study slip and associated folding on the Oak Ridge fault over the last 1.8 million years. We are creating structure-contour maps of two horizons to restore to an initial horizontal state using the program UNFOLD. An existing map of a 1 Ma horizon for onshore Ventura basin is being used (Yeats, 1981, 1989), while a grid of seismic reflection data is being used to modify the offshore part of that map. Seismic reflection and well data is being used to create a map of a ~1.8 Ma map offshore, while geologic maps and published and newly available industry cross sections are being used to construct the onshore map. All of the maps will be digitized and 3-D views of the structure created. Results to date include a lot of work towards gathering and interpreting the data and constructing the maps, including work by Kirsten Zellmer and Carmen Alex computer-generating maps of data. Reflections sampled by, and also deeper than Ocean Drilling Program site 893 have been correlated through dense grids of high-resolution seismic reflection data. An anticline in Santa Barbara Channel has increased in amplitude by ~2 mm/yr over the last 110-120 ka, and the Oak Ridge fault and related fold has increased in amplitude and the vertical component of slip by 1 mm/yr over the last 1 million years. Chris Sorlien National Science Foundation EAR-9706258 3/1/97 - 2/28/98 $22,735
Collaborative Research: Testing Models of Fault-Related Folding, Northern Channel Islands, California Christopher Sorlien is in the early stages of work on this collaborative project with Nicholas Pinter of ICS and Southern Illinois University to study deformation of the Northern Channel Islands (southern California). The goal of this project is to test models for creation of giant folds above blind faults. A published model interprets that the North-dipping backlimb of a northern Channel Islands anticline is 10 km wide, and that the dip-slip component on the blind fault is also equal to 10 km. However, alternative models exist that can explain this giant fold with less slip. Pinter and his graduate student will be surveying marine terraces on Santa Cruz and Anacapa Islands, because the inner edges ("shoreline angle") of uplifted marine abrasion platforms represent an initially horizontal line that has since been deformed. Sorlien will use high-resolution seismic reflection data to interpret sedimentation and erosion of the submerged shelf north of the islands. There is strong evidence that this shelf has subsided at least 100 m while the islands have been uplifted. This represents a down-to-the north tilting that it is not consistent with the published fold model, but is predicted by the alternate model. Initial stratigraphic correlations suggest that the strata that have subsided are several hundred thousand years old, or possibly much older. Rates of tilting are quite slow, and it is possible that the blind fault has been less active over the last half million or million years than it had been previously. Arthur Sylvester US Geological Survey 1434HQ96GR02732 4/1/96-9/30/97 $77,288
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: http://www.geol.ucsb.edu/~geodesy/whats_new.html Arthur Sylvester US Geological Survey 1434HQ97GR03132 4/1/97-3/31/98 $49,999
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. http://www.geol.ucsb.edu/~geodesy/ Alain Trial and Libe Washburn UC Energy Institute UCSB 08960644 7/1/96-6/30/98 $24,200
Impacts of Oil Production on Natural Hydrocarbon Seepage in the Santa Barbara Channel Determined by Fluid Dynamic Modelling 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 * 104 m3 per day. |
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Ralph Archuleta University of California, Office of the President Campus Laboratory Collaboration UCSB 08950868 7/1/95 - 6/30/98 $122,336
Seismic Hazard Study of the University of California Campus at Santa Barbara: Preliminary Results from the CLC Boreholes A multi-disciplinary seismic hazard study of the UC Santa Barbara campus is being conducted as part of a UC-LLNL program (CLC). The primary objective is to predict the ground motion at UCSB campus based on potential seismic sources and local site conditions. To date, the 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 ~1500m/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. 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 SCSN and SCEC data center at Caltech. Data from this experiment 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 Institute for Protection and Nuclear Safety OSSN/95-866/MG-VB 406000000470 11/26/95 - 11/25/97 $204,157 Nuclear Regulatory Commission NRC 04-96-046 12/20/95 - 12/19/97 $446,248
The 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 we deployed a liquefaction array at Garner Valley to examine how the very near-surface water saturated alluvium will respond to strong ground motion from nearby large earthquakes. Liquefaction occurs when large ground motions build up fluid pressure in a confined water saturated near-surface alluvial layer, and the soil strength is reduced to the point where the soil behavior is more like a liquid than a solid. The liquefaction array is a group of pressure transducers installed at different depths within the near-surface soil, to record any changes in the pore pressure during strong ground motion. This new data at GVDSA is critical for engineers to better understand and model the highly nonlinear process of soil liquefaction. Array experiments which use the surface wave dispersion of noise or vibroseis truck (big thumper) signals to examine near-surface soil velocity structure are a relatively inexpensive way to determine site response without the drilling costs. At GVDSA, two experiments in the past year were conducted to examine these techniques, and compare the results with the well known structure at the site. The noise experiment was performed by the USGS, and the vibroseis was performed by the University of Texas. With the detailed information from drilling and logging at Garner Valley, it is the ideal location to test these non-invasive techniques against a well know site. The results from these experiments should be available within the next year. In April of 1997, the third annual BVDA/GVDA meeting, which brings together researchers from France, Japan, and the US, interested in site effect studies and borehole data, was held in Honolulu, Hawaii, in conjunction with the Seismological Society of America annual meeting. We have a data exchange agreement with Japan to exchange earthquakes from our Garner Valley experiment with their Borrego Valley downhole array (BVDA) experiment. Each year we get together to discuss the past years activities and our current results. In the spring of 1997 Jamison Steidl of ICS spent six weeks working at the offices of our French sponsors (CEA), and then Jean-Christophe Gariel of the CEA came in the summer of 1997 to work at ICS. The idea behind these research sabbaticals is to increase the communication and collaboration between researchers at the two institutes. As a result, we are in the process of writing multiple joint publications between the institutes. The success of the visiting research program this past year means that next year we will again send one ICS researcher to France, and welcome a French researcher at ICS. In the next year a remote rock site station near the Lake Hemet dam, about 3 km from the GVDSA main station will be installed. A 30 m borehole instrument and a surface instrument directly above, will help to better understand the effects of the weathered rock layer on the earthquake ground motion. Radio modem telemetry will be used to communicate between the main station and the remote station. Plans for this new installation are almost complete, and we are now waiting for the new downhole accelerometer to arrive from the manufacturer to bring this new data on-line at GVDSA. http://www.crustal.ucsb.edu/gvda/
Ralph Archuleta National Science Foundation EAR-9219721 5/1/93 - 12/31/96 $96,338
How Do Earthquakes Generate Extreme Ground Acceleration ? The 1992 Petrolia Earthquake (M = 7.1) was quite remarkable in that an accelerometer at Cape Mendocino (CAP) recorded a high-frequency pulse of almost 2 g, whereas the nearby (roughly 6 km away) Petrolia station (PET) recorded a maximum of only 0.6 g. In our model for this event, we have investigated the possibility that extreme ground acceleration with high spatial variability can be caused by a source effect, specifically the rupture of a barrier/asperity. This type of rupture feature can produce extreme ground acceleration provided that certain geometrical constraints are met. In the present study, we derive a combined high- and low-frequency faulting model for the 1992 Petrolia earthquake, that is consistent with the slip distribution on the fault, and that produces the high-frequency pulse at CAP. Our model consists of four parts: 1) A low-frequency (0.1 - 0.6 Hz) inversion that determines the slip, rupture time, and rise time distributions on the fault; 2) An interpolation and perturbation of the above distributions that produces synthetic accelerograms between 0.6 and 3.0 Hz; 3) Random phase signal that is scaled to the spectral amplitude level of the data between 3.0 and 12.5 Hz; 4) The rupture of a barrier/asperity that produces greatly amplified radiation at CAP but not at other stations. We find that our model produces a good fit to the near-source records of the 1992 Petrolia event. The results emphasize the interaction between fault geometry and rupture propagation to produce ground motion, as well as the hazard associated with locations above the hanging walls of dipping faults, where the geometry permits the production of extreme ground acceleration. Ralph Archuleta National Science Foundation EAR-9416214 9/15/94 - 12/31/96 $64,896
Source Inversion Using Aftershocks As Empirical Green's Functions Strong ground motion time-histories of large earthquakes can be successfully simulated using recordings of small earthquakes (Empirical Green's Functions). EGF methods were introduced by Hartzell (1978) and extensively used for predicting effects of large earthquakes (Joyner and Boore, 1988; Aki and Irikura, 1991). We have developed a very efficient method that fully exploits the major asset of EGF's representing the whole path propagation effects from the seismic source up to the location of the recording instrument. The idea is the simulate the input motions at the base of the soil column at a site, and then propagate them using an observation of any earthquake at the same site. This concept is widely used in earthquake engineering where the propagation is performed numerically using a geotechnical model of the subsurface media. If one has a seismic record at the site, then the necessity of a detailed knowledge of the subsurface geology is eliminated. The computational procedure has the following steps. A large earthquake is modeled as a heterogeneous kinematic source in a homogeneous space (Aki and Richards, 1980; Spudich and Archuleta, 1987). The waves are propagated up to a certain depth determined by the regional velocity structure. Then we repeat the same modeling process for an observed earthquake. By comparing the observed waveforms with the corresponding synthetics we obtain an empirical site-specific transfer function which describes the propagation of seismic waves from the base to the surface. This transfer function is then applied to initial synthetic predictions of the large earthquake. The same idea allows an additional flexibility in performing source inversions. E.g., one no longer needs to fix the source geometry as the recalculation of the whole space Green's functions is very fast. Ralph Archuleta, Jamison Steidl, and Alexei Tumarkin US Geologic Survey 143494G2410 12/1/94 - 11/30/96 $105,407 LA Basin Microzonation The Los Angeles Microzonation project was a very successful endeavor in many ways. The project objective was to collect seismic data from sites throughout the Los Angeles metropolitan region for seismic hazard analysis. It has long been known that each soil type responds differently when subjected to ground motion from earthquakes. Usually the younger softer soils amplify ground motion relative to older more competent soils or bedrock. The different methods for quantitative analysis of site response estimation were examined in detail and the results reported. In addition, the project determined correlations between average amplification factors determined from seismic data and mapped surface geology. These results are of critical importance for predicting site response from future earthquakes. One of the primary reasons for the success of this project was the occurrence of the Northridge Earthquake, and also the collaboration between the co-authors in the resulting publication. The number of researchers using the data collected by this experiment is a testimony to the success of the project. While overall the project was a great success, it should be noted that there were also some failures. One of the important results from this experiment that is not reflected in the published work, but should be reported to the funding agencies, is where the failures did occur. Urban seismology is a difficult task, due to the level of ground noise in large metropolitan regions. The Los Angeles basin is no exception to this, and has an extremely high level of urban noise which makes microzonation using earthquake data from small events very difficult. Were it not for the occurrence of the 17 January 1994 Northridge earthquake this project could have been a complete waste of time and money. It is important to note that number of local earthquakes each year that produce ground motion above the urban noise level (throughout the Los Angeles basin) can in some years be one or zero. We were very lucky in that the pilot experiment for this project was up and running before, during, and after the Northridge earthquake. There have been numerous publications to date which use the high dynamic range digital data provided by this project. On the other hand, the main effort for the deployment of the instruments from PASSCAL, which did not arrive at UCSB until November of 1994, was very unsuccessful. The deployment took place from December of 1994 through July of 1995. During this time, only two events were large enough to be recorded on the entire array of 15 stations. What is needed is more permanent stations with high dynamic range that will record over a period of many years, the weak-motion earthquake data from the densely populated regions of Los Angeles basin. When moderate to large events do occur, these permanent stations can be augmented with dense arrays of portable stations, as was done after the Northridge earthquake. Short term (less than a year) portable deployments in noisy urban environments may not be worth the time and effort except in the case of robust aftershock sequences. Ralph Archuleta and Alexei Tumarkin University of Southern California Southern California Earthquake Center USC 572726 4/1/91 - 1/31/98 $347,600 Strong Motion Database (SMDB) and Empirical Green's Functions Library (EGFL) SCEC databases SMDB and EGFL were designed to provide an easy access for both seismological and engineering communities to the extensive collection of seismological observations. SMDB contains parameters and waveforms of the strongest ground shaking recorded in Southern California since 1933. SMDB played an important role in preparation of the Phase III report being instrumental in organizing data for attenuation relations and site amplification studies. It is extensively used by scientists and engineers to predict effects of future large earthquakes and seismic structural design purposes. EGFL contains parameters and unclipped highest quality waveforms of smaller earthquakes (we are currently processing M>3.5) recorded in Southern California since 1981. It provides means to calibrate numerical models of wave propagation, especially important for ground motion prediction and studies of the crustal structure, in particular, imaging of faults. Also weak motion data are used to estimate site-specific ground motion amplification. In 1996 we started working on the Web version of SMDB. The working version is already available to anyone with a Web browser through SMDB home page at http://smdb.crustal.ucsb.edu/. We have accomplished the following tasks: completed the development of the Web version of SMDB, including: ftp access to waveform data and on-line plotting of time histories; maps of user-defined events and stations; corrected and updated SMDB data; provided technical support for both Web and Sun versions. Alexei Tumarkin and Ralph Archuleta University of Southern California Southern California Earthquake Center USC 572726 2/1/95 - 1/31/98 $45,000
Empirical Time-Series Simulation of Phase-III Scenario Earthquakes We have continued to develop a multi-disciplinary approach to the problem of predicting of ground motions from scenario earthquakes. The methods we are using consist of a Theoretical Green's Functions (TGF) method, an Empirical Green's Functions (EGF) method, a hybrid method which utilizes both the synthetic Green's functions and arbitrary observation(s) of small earthquakes at the studied site, and our modification of the stochastic ground motion prediction approach. Simplified hybrid approach. This efficient technique is a follow-up on the previous SCEC-funded research (Tumarkin et al., 1996; Tumarkin and Archuleta, 1997). A similar method of kinematic modeling with empirical Green's functions has been developed by Larry Hutchings at LLNL. The basic idea is to simulate the input motions at the base of the soil column at a site, and then propagate these motions using an observation of any earthquake at the same site. This concept is widely used in earthquake engineering where the propagation is performed numerically using a geotechnical model of the subsurface media. The advantage of having a seismic record at the site is that the necessity of detailed knowledge of the subsurface geology is eliminated. A general computational procedure has the following steps: A large earthquake is modeled as a heterogeneous kinematic source in a theoretical model of the geologic medium (e.g., layered half-space). The waves are propagated to a given base-rock depth determined by the regional velocity structure. The same modeling process is applied to any observed earthquake that was recorded at the same site. By comparing the observed waveforms with the corresponding synthetics we obtain an empirical site-specific transfer function that describes the propagation of seismic waves from the base to the surface. This transfer function is then applied to initial synthetic predictions of the large earthquake. The simplified approach uses the wave propagation in a whole space: The target earthquake is modeled as a heterogeneous kinematic source in a homogeneous whole-space. The source is represented as a suite of physically plausible slip, rise-time and rupture velocity distributions. A representative time history can be obtained even assuming a uniform slip, constant rise-time and rupture velocity. The empirical site-specific transfer function is calculated by deconvolving a Brune's source time-function from the observed empirical Green's function. It is justifiable within the whole-space framework. Using empirical Green's functions one can obtain realistic results even assuming very simple source and propagation models. This results in a computer efficient procedure for calculating strong motion synthetics. Modified stochastic approach. The basic idea of the stochastic approach (SA) is that the ground motion is represented by a windowed and filtered white noise time series, where the average spectral content and the duration over which the motion lasts are determined by a seismological description of seismic radiation that depends on source size (Boore, 1983). Indeed the acceleration Fourier amplitude spectrum is effectively band-limited within the range determined by the source corner frequency f0 and the attenuation cut-off frequency fmax. The ease of implementing the SA approach and reasonably good results obtained with its help (e.g., Silva's and Chin-Aki's C-cubed simulations), makes it a widely used tool among engineers as well as seismologists. At the same time it is often criticized for being not able to catch the proper phase content of strong ground motions. During the last year we found ways to improve upon the standard SA techniques. Here are our modifications: We observed that the amplitude distribution of acceleration amplitudes is non-Gaussian. We found that the uniform distribution with an exponentially decaying envelope reproduces the observed behavior surprisingly well. In order to account for directivity we adjust the apparent source corner frequency according to the source-receiver geometry. We apply an envelope function to accounts for both S-P times (calculated from the hypocentral distance), differences in S and P amplitudes and attenuation. As the attenuation filter exp(-p*k*f) is physically unrealizable, we are using the following functional form: 2*cosh(p*k*f)/(cosh(2*p*k*f)+1). This procedure produces realistically looking acceleration, as well as corresponding velocity and displacement time series. We think that these results suggest a promising and efficient way to improve the quality of SA predictions. Ralph Archuleta and Kim Olsen US Geologic Survey 1434HQ97GR03100 3/1/97 - 2/28/97 $55,000
Three-Dimensional Ground Motion Modeling in the San Francisco Bay Area In collaboration with USGS, Ralph and I have initiated the 3D ground motion modeling in the San Francisco Bay area with sensitivity analyses concerning rupture velocity, directivity, and slip variation, and topographic scattering. We use a 60 km (E-W) by 70 km (N-S) by 25 km (depth) 1D velocity model used by USGS for earthquake location. We are in the process of simulating south-east and north-west propagating ruptures on the Hayward fault for constant and varying slip, several different rupture velocities, in models with and without topography. Currently, a 3D basin model of the San Francisco Bay area is being developed at USGS, which will be used included in the ground motion modeling when available. http://www.crustal.ucsb.edu/~kbolsen/BAY.html
Ralph Archuleta University of Southern California Southern California Earthquake Center USC 572726 4/1/91 - 1/31/98 $1,055,633 The Portable Broadband Instrument Center (PBIC)
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 Equipment usage picked up in late 1996 when ICS researchers deployed PBIC equipment on the UCSB campus. This was part of the seismic hazard assessment phase of the Campus Laboratory Collaborative (CLC) project. The array was expanded after the initial stations recorded the M4.1 Ojai earthquake. This array recorded some other interesting regional seismicity including the M3.6 Santa Barbara earthquake. Work is currently underway to deliver this data set to the SCEC data center. Dr. Monica Kohler's (UCLA) eight month long Los Angeles Basin Passive Seismic Experiment (LABPSE) began using all of the PBIC recorders in March. This deployment consists of eighteen seismic stations distributed from Seal Beach to the base of the San Gabriel Canyon, north of Azusa. The data collected from this array will supplement the active source data collected by the LARSE project in late 1994. 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 timelines for equipment usage prior to 1994. New sections include a field guide (under development) for using PBIC equipment and equipment tables for DASs and DRSs. Seismological demonstrations were presented at several local schools including Isla Vista Elementary and La Colina Jr. High. ICS graduate students participated in Santa Barbara's Earth Day '97 by setting up PBIC equipment in De La Guerra plaza and giving presentations and demonstrations throughout the day. Ed Keller University of Southern California Southern California Earthquake Center USC 572726 2/1/95 - 1/31/98 $69,000
Earthquake Hazard of the Santa Barbara Fold Belt Our discoveries in the Santa Barbara Fold Belt (SBFB) are providing new, fundamental information about how young developing fold belts are produced and the seismic hazard they present. Research accomplished in 1996-97 on the earthquake hazard of the SBFB funded by SCEC includes; 1) identification of previously unmapped strands of the Quaternary Mission Ridge fault system as well as associated and defeated paleo-channels of Mission Creek, 3) additional numerical dating of deformed emergent marine terraces in the SBFB, and 4) development of an exciting, new method of correlating emergent marine terraces using stable isotopes. Ed Keller US Geologic Survey 1434HQ97GR02978 12/1/96 - 11/30/97 $76,091
Earthquake Hazard of the Santa Barbara Fold Belt, California Our work on the earthquake hazard of the Santa Barbara Fold Belt (SBFB) is contributing important information on the tectonic activity and style of deformation of a developing fold belt. Our research on the earthquake hazard of the SBFB for 1996-97 funded by NEHRP includes: 1) detailed evaluation of several potential trench sites, 2) examination of several trenches excavated in cooperation with local consulting firms, 3) greater understanding of the style of shallow deformation in fold belts, 4) establishment of rates of uplift of the SBFB and faulting on the Mission Ridge Fault System (MRFS) near Isla Vista, and 5) discovery of geomorphic and cross-fault segment boundaries on the MRFS. Grant Lindley Nuclear Regulatory Commission NRC 04-94-079 8/5/94 - 8/4/97 $213,370 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. Craig Nicholson University of Southern California Southern California Earthquake Center USC 572726 2/1/95 - 1/31/98 $45,000
Seismicity Studies of the Santa BarbaraVentura Area The western Transverse Ranges are one of the most active tectonic regions of the world. In the Ventura Basin, faults and folds accommodate high rates of oblique crustal strain and uplift rates exceed 10 mm/yr. The 1994 M6.7 Northridge earthquake occurred on a blind, south-dipping fault beneath the San Fernando Valley that is considered part of the same fault and fold system that extends westward into the Ventura Basin and eastern Santa Barbara Channel. These active fault structures represent a significant seismic hazard to a large urban population, yet little is understood about these active tectonic structures or about the hazard associated with these blind faults, because little has been done to document the nature or subsurface geometry of these structures in 3D. In fact, much of what is "known" about these active faults and their associated folds has been inferred from simple 2D balanced cross section models, many of which have only limited subsurface control. The fundamental question is: Are any of these 2D balanced cross section models reliable as they are currently applied to the western Transverse Ranges especially in areas of oblique convergence? The purpose of the NSF project was to conduct just such an evaluation of published 2D kinematic fold models in the western Transverse Ranges using available seismic reflection, seismicity, and deep drillhole data. The project involved: (1) the acquisition of an unusual set of seismic reflection data for California, and (2) preliminary analysis of these and other data to evaluate the geometry of active subsurface faults and folds in the Ventura Basin. Within the Ventura Basin, the quality of the seismic reflection data proved disappointing owing largely to the complexity of the local structure and stratigraphy; however, combined with other data, especially seismicity, significant subsurface structure could be identified. A continuing SCEC funded project is a geophysical study of the velocity structure and seismicity of the Santa Barbara Channel and extending eastward into the Ventura Basin. Except for the recent seismicity of the 1994 Northridge sequence, few of the earthquakes in this area have ever been located with a velocity model that accounts for the known 3D velocity structure of the region. It was hoped that a reliable 3D velocity structure could be estimated by inverting earthquake phase data from the regional Southern California network. However, analysis of the waveforms archived at the SCEC Data Center indicates that much of the telemetered data at certain critical sites from the western part of the network near the Santa Barbara Channel suffer from cross-talk problems, and apparent phase arrival times are subject to large systematic errors. These problems inhibit the ability to invert the data for 3D velocity structure, but the data can be used to solve for improved 1D velocity models using progressive inversion and either exponential (L1) and Gaussian (L2) norm residual minimizations. Using an improved 1D model, earthquakes associated with the 1996 M4.1 Ojai Valley earthquake sequence were relocated. The revised hypocenters and focal mechanism nodal planes appear to define a previously unrecognized, active, curviplanar fault the extends from about 4 to 19 km depth in the footwall of the steeply dipping Santa Ynez fault. Other microearthquakes that extend from the Ventura basin into the eastern Santa Barbara Channel are associated with the predominantly strike-slip, south-dipping Santa Ynez and Arroyo Parida faults, while other events define a planar Red Mountain fault that dips north at about 45°. Evaluation of our preliminary seismicity results, in conjunction with the available seismic reflection and deep drillhole data, indicates that although the 2D fold models have proven useful in other tectonic regions where convergence is more uniform along strike, these models consistently fail to adequately resolve significant subsurface fault structure in this area. Active buried or blind faults typically have steeper dips, deeper depths, and non-planar geometryfeatures not replicated in many of the 2D modelsand several active faults are missing or are miss-identified in the 2D models. The primary reasons for this failure are the inappropriate assumptions used in the 2D models that ignore fundamental aspects of the regional deformation that include significant strike-slip or out-of-plane motion, crustal rotations, large variations in depositional thickness and material strengths of rocks, basin subsidence and pre-existing fault structure that preclude for the most part the simple ramp-flat fault geometry often adopted by the 2D models. This research was also supported by National Science Foundation EAR94-16194. http://www.crustal.ucsb.edu/hopps/
Kim Olsen University of Southern California Southern California Earthquake Center USC 572726 2/1/97 - 1/31/98 $25,000
Three-Dimensional Finite-Difference Simulation of a Dynamic Rupture After a fruitful stay at ICS during the summer of 1996, Raul Madariaga, Ecole Normale Superieure, Paris, and I in collaboration with Ralph Archuleta implemented the boundary conditions for simulating a spontaneous rupture in arbitrary 3-D earth models using a finite-difference method. The method combines the computational advantages of 3-D kinematic finite-difference modeling and the dynamics of the earthquake itself. We use the method to simulate the 1992 Landers earthquake with a realistic initial stress distribution. The simulated rupture propagates on the fault along a complex path with highly variable speed and rise time, changing the pattern of the stress dramatically. The dynamic rupture reproduces the general slip pattern used to compute the initial stress level and generates near-fault ground motions at the surface similar to observations. The modeling method may be used in the future for more realistic hazard estimation in earthquake-prone areas. http://www.crustal.ucsb.edu/~kbolsen/DYN.html
Kim Olsen Los Alamos National Laboratory F42200017-3Z 2/3/97 - 9/30/97 $27,000 General Support on Computations on Near-Surface Wave Amplifications in the Los Angeles Basin Researchers from the group EES-5 at Los Alamos National Laboratories and I are in the process of developing a hybrid finite-difference technique capable of modeling non-linear soil amplification from the 3-D finite-fault radiation pattern for earthquakes in arbitrary earth models. We use my 4th-order staggered-grid finite-difference method to generate linear Green's functions from the earthquake, and the non-linear modeling is carried out by the Los Alamos stress-wave modeling code SMC123. We use the 1994 Northridge earthquake as a test case for the method. Kim Olsen National Science Foundation EAR-9628682 8/15/96 - 7/31/97 $60,000 AND University of Southern California Southern California Earthquake Center USC 572726 2/1/96 - 1/31/98 $35,000 Simulation of Three Dimensional Ground Motion in Los Angeles from Large Earthquakes in Southern California We have used 3D/1D 3-sec response spectral ratios to construct amplification maps for the Los Angeles basin for eight earthquake scenarios. The earthquakes were simulated as elastodynamic propagating ruptures with constant slip on the faults in a 1-D and a 3-D model. Ratios of 3-sec 3D/1D root mean square velocity response spectra (5% damping) vary considerably between the scenarios in the LA basin. In particular, the amplification tends to increase with distance from the causative fault to the basin structure. The response spectral ratios for the eight scenario earthquakes are combined into an average LA basin amplification map. The LA basin is outlined by an average 3-sec response spectral ratio of 2 with a maximum value of 4.1. The sites associated with the largest mean 3D basin amplification effects are located above the deepest parts of the basin. http://www.crustal.ucsb.edu/~kbolsen/LA3D.html
Kim Olsen University of Southern California Southern California Earthquake Center USC 572726 2/1/97 - 1/31/98 $5,000
Participants in the 3-D Model Verification Study A primary objective of the 3-D model verification study is to provide interested modeling groups with the opportunity to compare their computational techniques on a set of common rupture scenarios in a common earth model (supposedly the San Fernando Valley model by Magistrale et al., 1996). The outcome of this study is extremely important, since the accuracy and numerical weakness and advantages of the different numerical modeling codes, gridding strategies, and methods incorporating realistic earthquake sources, as well as the accuracy of the 3-D earth model will be revealed. An important outcome of the study will be an organized coordination of future ground motion modeling efforts from different groups with thoroughly validated software, thereby prohibiting redundant work. I plan to run 3-D simulations of the predefined rupture scenarios. The results will be compared, expectedly during two different workshops, one in March 1997 for numerical verification purposes and one in September 1997 for model validation purposes. I plan to participate in both workshops. A strong personal interest in the study stems from the development of a 3-D elastic 4th order staggered-grid finite-difference code (Olsen, 1994) and my 3-D modeling work in the Los Angeles basin (e.g., Olsen et al., 1995; Olsen and Archuleta, 1996a,b,c; Olsen and Archuleta, 1995). I expect the results from the comparative study will provide important guidelines for a continuation of this important work. Jamison Steidl and Alexei Tumarkin University of Southern California Southern California Earthquake Center USC 572726 2/1/96 - 1/31/98 $85,000
Response Spectral Amplification Factors: Correlation with Geological and Geotechnical Site Characteristics The near-surface geological site conditions have been shown to be a dominant factor in controlling the amplitude and variation of strong ground motion, and the damage patterns that result from large earthquakes. In the past year we have been looking at response spectral amplification factors from weak-motion data, strong-motion data, and analytical models, and trying to find correlations 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. We compared results from two completely independent weak-motion site response studies of Northridge aftershock data. Stations are separated by site class and the site response at stations on the same site class are averaged. This is done for both the QTM site class (Quaternary, Tertiary, and Mesozoic), and a more detailed site classification, Qy, Qo+Ts, and M+Tb (Holocene Quaternary, Pleistocene Quaternary + Tertiary Sedimentary, Mesozoic + Tertiary Basement). The results showed that two completely independent site response studies (using different stations, events, and reference site) give very similar average results. In addition, the more detailed geologic site classification seems to separate out better the average site response on younger Quaternary sediments from the older Quaternary and Tertiary sediments. The empirical weak-motion results mentioned above are compared with site response estimates of strong-motion data in Southern California relative to a rock attenuation relation, and with analytical estimates of site response which contain nonlinearity at high input levels of ground motion. The strong motion database contains response spectral acceleration for all accelerograms in the database at 0.1, 0.3, 1.0, and 3.0 second periods. We calculated for each accelerogram in the database, the predicted rock response spectral motion using the rock attenuation relation for the same four periods. The ratio of the observed spectral ordinates to the predicted rock spectral ordinate is then used as an estimate of the site response at each site. We then examine the observed to predicted ratios by plotting them as a function of predicted peak ground acceleration to look for any nonlinear dependence on input motion. If we break up the ratios into bins of similar predicted rock PGA (input motion below the alluvium) we can look at the average site response with respect to the level of input ground motion to the site. We have used four bins: a low input bin (less than 0.05% g), two intermediate bins, and a large input bin (greater than 0.2 g). The average weak motion site response from the two previously mentioned studies are also compared. The independent weak-motion studies compare well with the low input level strong-motion results. The large input strong-motion data when compared with the geotechnical site response models suggests that non-linear behavior is present in the Southern California data set. Does site response correlate with basin depth or near-surface shear-wave velocity, or, does knowing basin depth or a nearby shear-wave velocity profile in the upper 30 meters help to explain the difference between the observed and the predicted ground motion mentioned above? We calculated the residual for each response spectral data point with respect to the average observed/predicted ratio for each site class and averaging bin and then compared these residuals to different geotechnical parameters. There is a definite trend in the residuals, showing larger than average site response for the deep part of the basin, and smaller than average for the shallow part of the basin. Averaging the residuals into three groups for shallow, intermediate, and deep parts of the basin, we get 20% larger site response for the deep basin, and 20% smaller site response for the shallow basin. The general trend can be fit by regression (straight line). In addition, low shear-wave velocity correlates with unconsolidated alluvium, while larger shear-wave velocity correlates with older more consolidated sediments or bedrock. As expected, there is a trend for larger than average site response at stations that have low shear-wave velocity in the upper 30 m from a nearby velocity profile. We can calculate averages for different velocity ranges and compute a regression curve (straight line), however, there is tremendous scatter at low velocity, and too few data at high velocity. More data points and analysis is needed to better understand the scatter in the data. Jamison Steidl and Ralph Archuleta University of Southern California Southern California Earthquake Center USC 572726 2/1/97 - 1/31/98 $195,000
New 1997 SCEC Borehole Instrumentation Initiative One of the major goals of the Southern California Earthquake Center is to compute theoretical seismograms for scenario earthquakes in the Los Angeles and Southern California region. The existing strong-motion data are used to calibrate and improve our computational techniques. Ground motions recorded at strong motion stations throughout Southern California are a combination of the complex earthquake source process, the propagation path from the source zone to the station, and the local near-surface site conditions at the station. The separation of source, path, and site effects is limited by the current availability of data, the detailed knowledge of the crustal structure, and our understanding of the earthquake source process. The widespread and varied ground motions and damage patterns over short distances produces a large degree of uncertainty in our ability to predict ground motion from future earthquakes. Much of the variability is thought to be caused by the local near-surface site conditions. In order to reduce the uncertainty in our ability to compute theoretical seismograms predicting the ground motion from future earthquakes, we propose to remove the near-surface site effect at a few select stations by installing borehole instrumentation below the surface soil layers. This new borehole instrumentation initiative will produce data that has not been distorted by the effect of the surface materials. This will allow for direct estimation of site effects, provide a test for the calibration and improvement of physical models of soil response, and 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 motion at surface sites in the region surrounding the borehole station. The new 1997 Uniform Building Code (UBC) to be used in the design of structures by the engineering community has placed a great deal of emphasis on the near surface soil conditions in the upper 30 meters. In fact, the site classification that will be used in this version of the UBC is determined by the shear-wave velocity or standard penetration tests in the upper 30 meters. Borehole geophysical data and seismic instrumentation for direct estimation of site effects at selected "typical" Southern California geologic site classes will help in calibrating and improving our physical models of soil response to different levels of ground motion. The degree of non-linear behavior in Southern California soils at large input ground motions is a critical issue for determining the maximum plausible ground motions from large earthquakes. Data provided by the up-hole/down-hole recordings of ground motion from the instrumentation deployed in this project will be stored with the Southern California Seismic Network (SCSN) data, and be available to both the earth scientists and the practicing engineers, so that these important scientific questions can be addressed. Results from a borehole study along the San Jacinto fault zone (Steidl et al., 1996) suggest that
the input wavefield below the near-surface sediments is much more coherent than at the surface, at soil
or rock sites, even over distances as great as 5-20 km. The implications of this result are that a small
array of borehole recordings can define the input motion for physical modeling of site effects within a
large region surrounding the borehole station. The shallow crustal environment in the region of the Steidl
et al. (1996) study, the peninsular ranges granitic batholith along the San Jacinto fault zone, is
quite different from that of the Los Angeles basin. Is borehole ground motion consistent over these
same scales across the Los Angeles basin, where the instrumentation will in some cases, due to the
great depth of the basin, be installed in stiff soil instead of granitic rock? The coherency of borehole
ground motion is most likely a function of the shallow regional crustal structure. This new borehole
initiative will address this issue by placing borehole stations in the rock at the edges of the Los Angeles
basin, and at different stations spacing away from the rock locations.
Stephen Cullen and Lorne Everett Lawrence Livermore National Laboratory B291841 03/08/96-09/30/96 $30,000
Evaluation of California's Leaking Underground Fuel Tank Program: Phase II Dr. Stephen J. Cullen has received follow-up funding to act as Principal Investigator to conduct continuation research to evaluate and recommend changes to the LUFT cleanup decision-making process in California. The purpose of the research effort is to identify, for the use of regulatory agencies and responsible parties, methodologies and approaches for dealing with leaking fuel tank problems. The goal of the resulting LUFT cleanup decision-making process is to determine the appropriate degree of regulatory response to leaking fuel tank cases that will ensure the protection of health and environment, including beneficial uses of the State's water resources. The developed methodologies are intended to avoid unwarranted expense, analysis, or delays while ensuring that adequate site characterization analysis is done to identify the extent of and design appropriate response to subsurface contamination problems. Previous research, in which Dr. Cullen and other ICS researchers participated, identified a modified risk-based corrective action approach to systematically meet this goal. The work to be performed under the Phase II research will accomplish three objectives. The first objective is to propose detailed customizations necessary to apply the American Society of Testing and Materials (ASTM) Risk-Based Corrective Action (RBCA) decision-making process to California environmental conditions under which LUFT cleanups take place. These proposed customizations to ASTM RBCA will reflect California's site-specific exposure pathways and quantify the uncertainty in the assumptions that are used during the LUFT cleanup decision-making process. The second objective is to perform ongoing data analysis of historical LUFT case data to support a customized RBCA approach, including the analysis of soils chemistry data, the application of a customized RBCA decision-making to historical LUFT case data, and the evaluation of passive bioremediation at active LUFT sites within California. The third objective is to evaluate the cost savings that may be realized to California's economy as a result of using a RBCA approach to LUFT cleanup. Stephen Cullen and Lorne Everett Lawrence Livermore National Laboratory B333265 10/1/96-12/31/97 $20,996 Petroleum Hydrocarbon Demonstration Project As a result of previous research published on the subjects of Leaking Underground Field Tank Cleanup in California and a Historical Case Analysis of California Leaking Underground Field Tanks, Dr. Stephen J.Cullen and Dr. Lorne G. Everett were invited to participate in a site specific independent review of Department of Defense environmental program site characterization data, implementation of risk based corrective action decision process with emphasis on passive bioremediation, and cleanup recommendations made to military base prime contractors. Drs. Cullen and Everett immediately saw the value of work of this nature and viewed this as an opportunity to further test conclusions developed in their prior research on site-specific contaminant problems. As a part of their participation in the expert committee formed to review Department of Defense Demonstration Program pilot sites, Drs. Cullen and Everett attend meetings at nominated sites to review site-specific characterization information regarding sources,pathways, and receptors. When applicable, Drs. Cullen and Everett participate in interactions between California State Water Resources Control Board, local public stake holder groups, and perspective pilot site teams. At each demonstration site, Drs. Cullen and Everett apply a tiered risk management approach, evaluate sources, pathways, and receptors for each demonstration site, identify the time frame for cleanup to meet local probable beneficial uses of groundwater, and determine the appropriate risk management action and levels of cleanup to address remediation of leaking fuel tank cases. Drs. Cullen and Everett intend on using the information and data gleaned from the site specific pilot test results to develop an analysis which compares a risk based corrective action cleanup process, with an emphasis on passive bioremediation, to base line cleanup approaches which rely on fixed numeric standards such as maximum contaminant levels and actively engineered processes such as groundwater pump and treat. Drs. Cullen and Everett anticipate that the results of this analysis will provide the basis for identifying the dominant petroleum hydrocarbon release scenarios within representative California hydrogeologic settings and use them to develop categorization of sites that could lead to risk management approaches based on shared data. Additionally, Drs. Cullen and Everett anticipate that they will be able to begin the process of integrating, identifying, and applying a suite of characterization, monitoring and remediation options that are technically and economically feasible for use in a California specific risk based corrective action framework to support a petroleum hydrocarbon risk management strategy that incorporates passive microbial degradation of contaminated sites. Lorne Everett Office of Naval Research ONR BPA N47408-96-A7023 05/20/96-03/31/97 $5,149
Vegetative Analysis for the Landfill Cover Demonstration Lorne G. Everett, directed research conducted in the Vadose Zone Monitoring Laboratory related to landfill and hazardous waste cap design. In particular, soils from Hawaii were sent to the Vadose Zone Monitoring Lab and 30 separate test chambers were developed to calibrate time domain reflectometry probes. The TDR probes are used to determine leakage rates associated with the landfill barrier cap designs. This research is funded by the United States Navy. The calibration chambers and testing procedures developed at the lab are expected to be utilized by the Navy at landfill sites throughout the world. Lorne Everett US Navy IPA A95002 03/15/95-09/30/97 $54,934 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. Hugo Loaiciga Bechtel Nevada PO 13440 2/1/97 - 8/15/97 $46,678 Current Practice of Environmental Characterization and Monitoring Technologies This project, is to document current practices of environmental technologies in the areas of site characterization and in situ remediation process monitoring. This activity, in a six month work period, will (1) collect, assess, and compile information from technology users and purchasers in DOE environmental management programs and (2) produce a draft document for review by technology users, purchasers, and project sponsors. The document will then be published in hardcopy form and on the Internet as a pdf (Adobe Acrobat) file. The Institute for Crustal Studies at the University of California, Santa Barbara, will assist in all the tasks and, in particular, express its expertise in geohydrological and geophysical aspects of the study. |
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