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The annual SCEC Intern Colloquium (pictures) and Field Trip (pictures)
was held August 3-6. The Colloquium has held on the first day.
After everyone introduced themselves and Intern Program Coordinator
Mark Benthien provided an overview of the the next four days,
USC Professor Thomas Jordan gave a presentation on the history
and future of SCEC. Outreach Director Jill Andrews then gave
a presentation about SCEC's Outreach programs. For the remainder
of the Colloquium each intern shared their project and its status
mid-way during the summer.
Online versions of the Intern presentations
will be added to the SCEC Website over the month of August. Click
on the following links to view the third set of presentations
by four of the ten interns. The first
and second sets were previously
added to this website.
Kevin Mass
Whittier College
Pressure
Solution Slip-faulting Associated with the Quatal Thrust Fault
Mentor: Jan Vermilye, Whittier College
This project is based on the analysis of
pressure solution strain measurements to infer stress orientations.
Vermilye and Seeber [1999] conducted similar research on the
San Cayatano fault. We plan to apply this same methodology to
the Quatal fault.
Pressure solution involves the process
in which grains dissolve along the contacts where compressive
stress is the greatest. Evidence of pressure solution is contained
in the sandstone and conglomerate outcrops throughout the region.
In conglomerates, the squeezing together of cobbles results in
indentations on the cobble surface. This indentation forms perpendicular
to the maximum compressive stress. These strain measurements
can be analyzed to infer the principal stress orientations.
Other deformation structures, such as small
pressure solution slip-faults, can be used to infer the principal
stresses. Field measurements of fault orientations and displacements
are taken at many locations. The data are analyzed using the
methodology of Michael [1984] and a program by Allmendinger et
al. [1989]. Each field location are analyzed in order to interpret
the principal compressive (s1) and extensional (s3) axes. Since
the Quatal fault is a thrust fault, we expect the inferred stresses
to reflect a typical thrusting regime, with sub-horizontal compression
and near-vertical extension. Finally, we offer possible explanations
for the variability of stress orientations between individual
locations.
Allison Jacobs
UC San Diego
The
Use of Interferometric Techniques to Monitor Crustal Strain and
Deformation Along Faults in South Eastern California
Mentor: David Sandwell, UCSB
In this project, I have studied the crustal
strain and deformation along two faults in South Eastern California
using interferometric techniques. The two faults involved in
this study are the San Andreas, particularly in the Mecca Hills
and Indio area, and the Lavic Lake fault, site of the 1999 Hector
Mine earthquake. Both of these areas of California are tectonically
active, and therefore, scientists continually search for new
and better ways to measure this crustal motion. Interferometry
has become one of the newest types of monitoring systems because
it provides more precise measurements of small-scale deformation
compared to the current widespread system of using a relatively
coarse distribution of GPS monitors. Working with David Sandwell
at Scripps Institution of Oceanography, I am utilizing many of
his interferometry resources to investigate several questions
involved with crustal deformation: First, is interseismic strain
concentrated with a 4 km region of the San Andreas fault, secondly,
are there significant variations in the amount of strain along
the San Andreas fault, and lastly, what type of co- and post-seismic
displacement is seen in the Hector Mine area? These questions
will mostly be answered by using archive and near-real-time interferometry.
In the future, the formation of interferograms on a regular basis,
especially of the Southern California area, will allow scientists
to observe increasing rates of crustal strain and thus issue
warnings of faults with high breakage (earthquake?) potential.
To answer my questions, I must first form
the interferograms. One of our main goals is to make a near-real-time
interferogram. By working at the Scripps Institution of Oceanography
satellite ground station, I am on-site when the ERS-2 spacecraft
flies along Tracks 127 (Hector Mine) and 356 (Mecca Hills) and
transmits near-real-time synthetic aperture radar data (SAR)
to the station. After each fly-over, I will extract a frame of
data from the respective flight that matches a frame from the
WInSAR (Western North America InSAR) data archive. Assuming all
goes well, these two frames of data will be processed together
to form a near-real-time interferogram. However, as science rarely
goes as planned, the near-real-time data can be saved a made
into an archived interferogram at a later time. In addition to
the near-real-time interferograms, I am forming interferograms
from archived data in order to add validity to my research.
Clay Stevens
CSU Northridge
3D
excavation across the San Andreas fault
Mentor: Doug Yule, CSU Northridge
My project will complement part of a larger
study that explores the earthquake history of the San Andreas
fault system near Banning, California. I hope to create a three-dimensional
fence diagram of the area using the information of previously
logged trenches and new trenches that will be opened this summer.
Once familiar with the site stratigraphy, I will build a fence
diagram using key structural and stratigraphic features, including
faults, folds, marker beds, and event horizons. The relative
positions of these features can be surveyed using a laser theodolite
total station. These data will then be plotted using GIS software
(Arcview or other equivalent software) to create the fence diagram.
I will also make hand drawn logs and photo mosaics to show the
key relationships. The fence diagram will provide a basis for
approximating the shape of event horizons. The geometry of the
paleo-surface can be constrained by extrapolating the event horizons
between trenchcrops based on the available structural and stratigraphic
information. A 3D approximation of each event horizon can show
how the ground changed relative to each earthquake event going
back in time. Once this is done we can estimate how much deformation
occurred during the paleo-seismic events. This information will
help constrain the magnitude of the earthquakes that rupture
through the Burro Flats site. I anticipate spending 5-6 weeks
in the field mapping and surveying the trenches, and ~5-6 weeks
preparing the 3D fence diagram. Computer labs at Caltech and
CSUN will be used to prepare the report and draft the diagrams.
Teresa Baker
Massachusetts Institute of Technology
Measuring
and Modeling Postseismic Motion of the Hector Mine earthquake
Mentor: Susan Owen, USC
Following the October 16, 1999 M7.1 Hector
Mine earthquake, there has been
a focused effort to collect postseismic deformation data. This
data has been collected by campaign and continuous setups of
GPS receivers, starting just 48 hours after the temblor. By measuring
the postseismic deformation we can quantize the short-term after-slip
and relaxation of the crust. Using this data we mapped the velocity
of each GPS station. Then we modelled the fault plane at depth
using simple dislocations in an elastic material. Using Matlab
and inverting the data we determine the fault slip distribution
that best fits the postseismic time series. This includes looking
for the depth of afterslip and modeling the fault plane(s). We
also looked for time constants for decay in the velocity observed
in the time series. Studying and modelling the data aids in a
better understanding of fault mechanics, the earthquake cycle
and the rheology of the crust.
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