Olsen and Archuleta numerically simulated ground motion from hypothetical M
6.75 earthquakes on the Palos Verdes, Santa Monica, and Elysian Park faults,
and the January 17, 1994 Northridge earthquake. A key factor in the models is
a new 3-D determination of the deep sedimentary basin underlying the Los
Angeles region. Their calculations showed strong amplification of motion due
to the 3-D basin structure. Peak ground velocities were up to an order of
magnitude higher above the basin (up to 67 cm/sec) compared to surrounding rock
sites. While the Northridge earthquake was incredibly damaging to the Los
Angeles area, the 3-D simulations show that earthquakes with the same magnitude
on the Palos Verdes or Elysian Park faults produce more severe ground shaking
in the Los Angeles Basin.
Using MIT's nCUBE2 parallel computer, Olsen and colleagues calculated two
minutes of 3-D wave propagation in the Los Angeles basin for a magnitude 7.75
hypothetical earthquake on the San Andreas fault east of Los Angeles. Strong
shaking was computed over the Los Angeles basin; the simulation showed peak
velocities up to 1,400 cm/sec, almost 10 times as large as that for rock sites
outside the basin at similar distances from the earthquake. Their simulation
study demonstrates that 3-D basin structure can significantly amplify the
ground motion. The results were published in Science (Olsen et al., 1995).
Cullen and Everett recently co-authored two reports that have impacted
traditional approaches to groundwater remediation in California and have had
substantial national impact on the cleanup of petroleum hydrocarbons which have
leaked to the subsurface.
A University of California team from several campuses and Lawrence Livermore
National Lab issued two reports. One report entitled "Recommendations to
Improve the Cleanup Process for California's Leaking Underground Fuel Tanks
(LUFTs)" recommended that passive bioremediation be considered as a cleanup
alternative. A second report entitled "California Leaking Underground Fuel
Tank (LUFT) Historical Case Analysis" showed that the dissolved phase
hydrocarbon plume length changes slowly and tends to stabilize at a relatively
short distance from an underground storage tank release site. Plume length
analysis showed that site plume lengths rarely exceed about 250 feet. Only
one-half of one percent of the underground fuel tank groundwater contamination
sites caused a drinking water problem. The potential volume of groundwater
impacted by LUFT plumes with greater than one part per billion benzene was
estimated to be .0005% of California's total groundwater basin storage
capacity. They concluded that current LUFT decision-making processes do not
result in cost effective site closures and that fuel hydrocarbons have limited
impacts on human health, the environment, and California's groundwater
resources.
The University of California report has resulted in substantial policy changes
which will allow scarce remediation dollars to be applied to more immediate and
serious problem sites.
Luyendyk and Bartek conducted a study of the Cenozoic glacial and tectonic
history of western Marie Byrd Land (MBL) and the eastern Ross Sea, Antarctica,
in winter, 1996. Their approach was an offshore marine geology and geophysics
study of the unexplored continental margin here using the U.S. icebreaker
N.B. Palmer (cruise NBP-9601).
A unique aspect of this project was that Luyendyk brought along 7
undergraduate students; six from UCSB and one from the Univ. of British
Columbia. These students were enrolled in a class given at sea. They also
have individual responsibilities for independent projects using 9601 data.
Cruise data reveal that the inner shelf in the Marie Byrd Land region has been
stripped of sediment by glacial erosion and that much of this sediment has been
deposited near the shelf edge in the region. Evidently a very different mode
of glacial marine deposition is occurring in the inner shelf basins of the
Marie Byrd Land region as compared to other regions of Antarctica. Geophysical
data map faulted half grabens in the continental shelf of the eastern Ross Sea
and western Marie Byrd Land trending subparallel to mountain ranges onshore.
These grabens, or valleys, apparently route the flow of outlet glaciers from
the continent onto the shelf. These structures are younger than the age of
breakup of the Antarctic continent from Gondwana about 100 to 85 million years
ago. Rather, they are associated with rifting and faulting in the Ross Sea
prior to glacial development.
This three-year project is part of the Campus Laboratory Collaborative (CLC)
initiative to foster more collaborative research between the UC campuses and
the national laboratories. The purpose of this project is to estimate the
anticipated seismic shaking from future earthquakes at four UC campuses--Santa
Barbara, San Diego, Los Angeles and Riverside. The location of faults, the
activity of faults, and the style of faulting, will be determined for each
campus. At each campus the subsurface geology will be determined from logs of
boreholes and seismic profiling. Once the subsurface geology is known,
boreholes will be drilled so that downhole seismometers and accelerometers can
be placed in competent rock below a building. A matching set of sensors will
also be placed at the ground surface. Geotechnical logs of the elastic
parameters of the material between the surface and the deepest part of the
borehole will provide parameters to theoretically predict seismic
amplification. By comparing the borehole recordings with the surface
recordings of earthquakes, the amplification of the seismic waves will be
determined empirically. Assuming that the theoretical and empirical
measurements are in agreement the measured subsurface structure over the entire
campus can be used to extrapolate the amplification to other parts of the
campus. The ground motion expected from large earthquakes will be estimated by
summing the recordings of small earthquakes as well as using theoretical 3D
simulation methods.
Prolific natural gas seepage occurs offshore from Coal Oil Point near Santa
Barbara, above the South Ellwood Offshore Field. Luyendyk and colleagues have
been studying this seepage field in order to determine the volume of seepage,
the time variation in seepage, and its possible cause. Seepage rates can be
quantified by measuring sonar reflections from gas bubbles rising through the
water column. In 1995 they digitally recorded 3.5 kHz sonar data in the same
location as a 1973 survey. Comparison of the data indicates a substantial
reduction in seepage within one mile of oil Platform Holly since 1973. The
physical mechanism that is responsible for the natural seepage is the flow of
hydrocarbon fluids from the oil reservoir to the sea floor through natural
fractures in the rock. The flow rate is controlled by the pressure difference
between the oil reservoir and the sea floor; as oil has been produced the
reservoir pressure has decreased. In order to develop an empirical data set on
time variations, they are analyzing sonar data acquired in 1980, 1981, 1982,
1983, and 1984 in the vicinity of Platform Holly. This would enable the timing
of seepage reduction relative to the decrease in reservoir pressure to be
compared against model predictions.