Communication, Education and Outreach (CEO)
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Communication, Education and Outreach (CEO) |
| 2000 SCEC Interns |
SCEC INSTANeT articles about the 2000 Internship program:
SCEC Summer Interns attend Communication Workshop and Orientation
2000 SCEC Intern Colloquium and Field Trip
SCEC Intern Colloquium Presentations, Part 1
SCEC Intern Colloquium Presentations, Part 2
Interns and their projects:
| Intern | Institution | Mentor | Project Title |
 Marie Ammerman |
UC Santa Barbara | Ralph
Archuleta UC Santa Barbara |
Inconclusive Evidence for Fault Zone Trapped
Waves on the Bullion Fault |
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 Teresa Baker |
Massachusetts Institute of Technology | Susan Owen Univ. of Southern California |
Afterslip Models of Postseismic Deformation from the 1999 M7.1 Hector Mine Earthquake |
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The postseismic deformation field follows the expected pattern of continued right-lateral displacement. The highest velocities occur 20-40 km from the surface rupture and the velocities subsided significantly over a nine month period. The velocities decay rapidly in the first month following the earthquake and more slowly afterwards. Taking this into account, we have modeled the distribution of slip over three time periods. In the model, the fault extends from the surface rupture to 40 km depth and also extends 20 km beyond the ends of surface trace. This fault surface was then discretized into 2 km by 2 km squares, and we estimated the slip on each square, applying a smoothing constraint to regularize the slip distribution. While variations in data quality over these different time periods affect our model resolution, it appears that the region of maximum slip moves northeast along the fault over time. |
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 Allison Jacobs |
UC San Diego | David Sandwell UC San Diego |
Hector Mine: Postseismic Deformation from ERS InSAR |
 The Hector Mine earthquake occurred on October
16, 1999, in the Mojave Desert of California. Four days later,
the European Space Agency satellite, ERS-2, flew over the region,
bouncing radar waves off the desert surface to produce the first
co-seismic synthetic aperture radar (SAR) image of the area.
The collection of this data was also highly important for studying
postseismic deformation since the most significant earthquake
deformation usually occurs within the first 40 days after the
main shock. We were fortunate to match this key image with data
received on June 21, 2000, at the Scripps Institution of Oceanography
satellite ground station, and create a postseismic interferogram
covering this critical time period. Using the interferogram we
contoured the line-of-sight (LOS) displacement in the fault region.
The three main deformation features seen in the line of sight
displacement map are a region of subsidence (40 mm line of sight
increase) on the northwestern side of the fault, a region of
uplift (65 mm line of sight decrease) located to the northeast
of the primary fault bend, and a linear trough running along
the main rupture of the fault. These features coincide well with
a characteristic left-bending, right-lateral strike-slip fault
that ideally exhibits contraction on the restraining side of
the fault bend and extension along the opposite side. In this
initial postseismic interferogram, the areas of subsidence and
uplift combine to display a maximum amount of displacement of
nearly 105 mm. A second interferogram made from images taken
39 days and 139 days after the earthquake shows a significant
decrease in the amount of displacement (maximum displacement
of 50 mm). This smaller deformation indicates that most of the
relaxation occurs within about 40 days of the main shock. The
co-seismic and postseismic interferograms created for this study
are on display at http://topex.ucsd.edu. |
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 Alexandra Jordan |
Univ. of Southern California | Mark Benthien Univ. of Southern California |
Setting the Stage for a HAZUS User Group in Southern California |
 This summer I worked on a project with Mark Benthien
and Jill Andrews to help promote the computer application, HAZUS.
HAZUS, or "Hazards US", is a PC-based Geographic Information
Systems software used for earthquake loss mitigation. The application
is used to collect an over report of the amount of damage that
may occur to one area affected by an earthquake. Our main goal,
along with working with HAZUS and learning more about the application,
was to help form a Southern California User Group. At the beginning
of the summer we traveled to the San Francisco Bay Area and joined
a workshop for users of the already existing Bay Area User Group.
By observing and talking with many of the participants we were
able to get an idea of the future goals and accomplishments geared
toward the formation of a Southern California User Group. The
Bay Area User Group has acted as a model for the kind of user
group we are hoping to establish. To gain more knowledge on what
people in the southern California region already know and think
about HAZUS, I designed a survey of 10 questions related to the
application. I called between 25 and 30 people and asked them
about their interests and knowledge of HAZUS. Most people seemed
enthusiastic to participate in future functions related to HAZUS
and hoped to hear more information about our progress. These
results will provide the SCEC Board of Directors with the information
needed to structure a Southern California User Group. |
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 Kevin Mass |
Whittier College | Jan Vermilye Whittier College |
Pressure solution slip-faulting associated with the Quatal thrust fault |
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The geometric and kinematic data are analyzed using the methodology of Michael (1984) and a program written by Allmendinger et al. (1992). The Michael (1984) analysis produces the orientation of the principal stress axes in the form of eigenvalues and eigenvectors. Allmendinger's program produces contour stereoplots of the P-axis (contraction) and T-axis (extension), as well as a fault plane solution plot representing the maximum strain directions for the combined data set. The results of these analyses show the inferred stress and strain orientations at six locations throughout Quatal Canyon. The stress and strain orientations are displayed as stereoplots. The contraction and extension strain axes appear remarkably similar to the tension and compression stress axes, respectively. Therefore, it is valid to assume that the principal stress axes can be found using strain deformation structures. While a composite strain analysis indicates a typical thrusting regime, with sub-horizontal compression and near-vertical tension, individual outcrops show variability. A spatial explanation for this involves inhomogeneous stress around the fault due to the irregular shape of the Quatal fault. A temporal explanation involves translation of the Quatal fault along the San Andreas fault from the Garlock fault intersection to its present location. |
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 Nancy Natek |
University of New Mexico | Mousumi
Roy University of New Mexico |
Constraints on the SCEC 3D Velocity Model
from Gravity Data: Two-Dimensional Gravity Modeling of the Central
and Eastern Transverse Ranges in the Los Angeles Region |
 The goals of this project are to test the consistency
of crustal seismic velocity structure and gravity data in the
Transverse Ranges. Following earlier work by Roy and Clayton,
we use 2D gravity models based on density structures inferred
from crustal tomography. We use version 2 of the Southern California
Earthquake Center (SCEC) velocity model and an empirically derived
scaling relation between seismic velocities and density. The
density structures thus inferred are used to forward model gravity
along 2D profiles.We plan to compare predicted gravity along four 2D topographic profiles across the central and eastern Transverse Ranges to the observed gravity. This report shows our preliminary results for one of the profiles, with work in progress on the other three profiles. We find that, in general, gravity data and crustal tomographic structures are consistent with each other. However, we find that there are significant misfits in the eastern LA Basin and in the Mojave Desert. In order to obtain a good fit in the LA Basin, we were required to increase average densities in the basin, reducing the size of the negative Bouguer signal from basin sediments. The gravity anomaly in the Mojave Desert section of the profile is more negative than predicted, suggesting the presence of a subsurface crustal mass deficit. This region can be well-matched by increasing the depth to the Moho under the Mojave Desert, or, as shown by Roy and Clayton, by reducing average crustal densities in the Mojave. |
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 Tracy Pattelena |
Pasadena City College/ UC Santa Cruz | Kim Olsen UC Santa Barbara |
Refinement of Near-Surface P and S Wave
Velocities in the SCEC 3-D Velocity Model Using 3-D Waveform
Modeling |
 An important part of ground motion studies opts
to predict full theoretical seismograms for an earthquake at
a given site. Our study focuses on the ground motion in a portion
of the San Fernando Valley (SFV) where control on the near-surface
S wave velocity, a critical parameter for accurate prediction
of strong ground motion, is mostly indirect and in many areas
not well constrained. We use 1-Hz 3D finite-difference simulations
to propagate waves for a M=5.1 Northridge aftershock through
two 10 km by 10 km by 5 km models of the SFV subsurface: (1)
a subset of the SCEC southern California reference 3D seismic
velocity model (version 2.0), and (2) model 1 modified with slower
velocities in the near-surface material taken from a tomographic
model. Model 2 contains near-surface P and S velocities up to
70% and 50% less than those of model 1, respectively, in the
upper 500 m. Compared to the response of model 1, the tomographically
refined model (2) generates peak ground velocities (PGV) and
cumulative kinetic energies (CKE) up to a factor of two in localized
areas of the model. While the synthetics for model 2 improve
the fit to data at the five stations only slightly, our simulations
suggest that version 2.0 of the SCEC velocity model is not complex
enough to reproduce the 1-Hz duration and peaks in the SFV basin. |
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 Daniel Raymond |
UC Irvine | Lisa Grant UC Irvine |
Seismic Hazard Assessment of the San Joaquin Hills using GIS |
 The San Joaquin Hills region of Orange County is
undergoing rapid commercial and residential development. The
anticlinal structure of the area is likely due to a combination
of tectonic uplift and seismic activity on local fault systems.
The goal of this project was to determine the hazards of the
fault zones in the area while there may still be time to translate
these findings into sound planning practices for the area. Geotechnical and fault investigation reports were collected for as many sites as possible in the San Joaquin Hill region. The findings from these reports were then collected and transferred to a GIS-based map. This map was designed in such a way to allow a convenient regional view of report coverage and findings, and was linked to a more complete bibliography created to display report titles, conclusions and relevant trench logs. Because little conclusive or comprehensive information was found during this study, a strong case can be made for the need for further fault investigations in the San Joaquin Hills region. |
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 Paul Rundle |
Harvey Mudd College | John Rundle University of Colorado |
Nonlinear Network Dynamics on Earthquake Fault Systems |
 Earthquake
faults occur in interacting networks having emergent spacetime
modes of behavior not displayed by isolated faults. Using simulations
of the major faults in southern California, we find that the
physics depends on the elastic interactions among the faults
defined by network topology, as well as on the non-linear physics
of stress dissipation arising from friction on the faults. Our
results have broad applications to other leaky threshold systems
such as integrate-and-fire neural networks. |
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 Clay Stevens |
California State University Northridge | Doug Yule California State University Northridge |
Three-dimensional excavation of the San Andreas Fault at the Burro Flats Paleoseismic site near Banning, California |
 Evidence from trenches opened in 1999 at Burro
Flats suggested that the San Andreas fault at San Gorgonio Pass
has remained dormant since about A.D. 1450. However, the 1999
trenches exposed a limited area of a complex, 150-m-wide stepover
basin and may have missed evidence of more recent event(s). This
summer an expanded trench network was excavated to search for
evidence of more recent events. The new trenches show clear evidence
of post-A.D. 1450 faulting and folding. The focus of my SCEC
internship has been to construct contour maps of marker horizons
and isopach maps of the intervening strata deposited in the last
550 years. Three marker horizons have been mapped over an area
of about 1000 square meters. Marker horizon 84, near the base
of the 550 year-old section, is faulted and folded into a syncline-anticline-syncline
triad with a maximum structural relief of about 1.5 m that diminishes
gradually to <0.25 m from south to north. Horizon 85, in the
middle of the section, is not faulted and shows a maximum structural
relief of about 0.6 m that also diminishes to the north. Horizon
88, near the top of the section, shows structural relief of 0.3
m or less. The modern ground surface is undeformed, dipping uniformly
toward the southwest perpendicular to the fault. Sediment above
horizon 85 is interpreted to have buried the folds and minor
faulting that formed during the most recent event. Horizon 84
drapes a paleo-surface created by the penultimate event. The
greater structural relief of horizon 84 is therefore attributed
to deformation from both the most recent and penultimate events.
Age data constrain the most recent event to between A.D. 1500
and 1800 and the penultimate event to between A.D. 1400 and 1550. |
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 Kathryn van Roosendaal |
California State University Northridge | Bob De Groot Univ. of Southern California |
Seismic Sleuths 2001: Revision of a Tool
of Scientific Literacy and a Renewal of Outreach Partnerships
at the Southern California Earthquake Center |
 Seismic Sleuths, an earthquake education curriculum
for grades 7-12, was developed jointly by AGU and FEMA in 1995.
In 1999, NSF funded a revision of the curriculum under the direction
of the Southern California Earthquake Center (SCEC). Revisions
will reflect advances in science and technology especially the
use of geodesy in earth science. This effort will provide an
innovative opportunity to improve earth science education in
several domains. Instruction in the classroom generally centers
on teaching the conclusions of scientific investigation. Seismic
Sleuths 2001 will be a resource for a basic integrated approach
to the study of seismic phenomena while being a doorway into
current research and controversies in earth science. The curriculum
will harness the power of the World Wide Web forming partnerships
across academe, government, and industry in order to tap the
multi-disciplinary nature of earth science. The primacy of relevance,
so well demonstrated in the original curriculum, will be enhanced
and expanded to include issues related to all hazards that face
citizens in the United States. Seismic Sleuths 2001 will allow
individuals to make sense of the world around them, take action
to reduce risk, and use technology that is an integral part of
their lives without eclipsing the science that comprises the
backbone of the curriculum. |
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Phone 213/740-5843
Fax 213/740-0011
e-mail: SCECinfo@usc.edu
Aftershocks
recorded by stations in the Bullion Wash Array lacked the arrival
of seismic waves that characterize the fault zone trapped waves
observed by Li et al., 1994. The arrivals following the S wave
were more prominent on fault parallel and vertical components
of the seismometers than on the fault perpendicular components-
inconsistent with a Love wave type mode trapped in a fault zone.
The waves following the S wave did not show consistent amplitudes
on stations within the fault zone with a decrease in amplitude
for stations farther away from the fault trace. The apparent
lack of fault zone trapped waves may be due to the juvenile nature
of the Bullion fault zone, i.e., it is not well enough developed
to generate trapped waves. The observed post-S waves may be basin
edge generated waves caused by a wedge of sediments that underlies
the array (Dibblee, 1967). The presence of edge generated surface
waves would explain why the waves are more prominent on fault
parallel and vertical components.
Following the
October 16, 1999 M=7.1 Hector Mine earthquake there has been
a focused effort by SCEC researchers to collect postseismic surface
deformation data in the region surrounding the fault rupture.
Using campaign and continuous GPS data collected by SCIGN, the
USGS, USC, UCLA, UCSD and MIT, we calculated postseismic velocities
at more than 50 sites. By measuring the postseismic deformation
we can quantify the crustal response to the earthquake and model
the distribution of afterslip on the fault at depth. This is
important for understanding the mechanics of the lower crust
and the postseismic period of the earthquake cycle.
This study is based on the analysis of pressure
solution strain structures to infer stress orientations. Sandstone
and conglomerate outcrops located in Quatal Canyon (northern
Ventura County, CA) have many types of pressure solution deformation
structures. Small pressure solution slip-faults (cm to m in length)
are a type of deformation structure that can be analyzed to infer
the local and regional principal stresses. Field measurements
of these faults are recorded at six locations in Quatal Canyon.
These six data locations are then combined in order to determine
the regional inferred stress axes.