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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 second set of presentations
by three of the ten interns. The first
set were added to this website last week.
Nancy Natek
Univ. of New Mexico
Constraints
on the SCEC 3D Velocity Model: 2D Gravity Modeling of the Transverse
Ranges
Mentor: Mousomi Roy
Gravity can be a useful tool in constraining
seismic tomography. In this project we develop a 2D gravity model
based on version 2 of the Southern California Earthquake Center
(SCEC) 3D velocity model to constrain the tomographic model.
The 3D seismic velocity model for Southern California in the
Los Angeles region is a crustal tomographic model of P-wave and
S-wave velocities reflecting density structures. This study is
based on previous work by Roy and Clayton for version 1 of the
SCEC 3D velocity model which showed that the seismic tomography
was in general consistent with gravity but with some discrepancies
in the LA Basin and Transverse Ranges. In the preliminary part
of our study shown in the slides below, we compare four 2D topographic
profiles across the central and eastern Transverse Ranges to
Airy Compensation models and observed gravity. In our current
research we are using scaling relations of Vp and density to
calculate the crustal density variations from the SCEC 3D velocity
model and comparing the observed gravity to the predicted gravity.
Tracy Pattelena
Pasadena City College/ UC Santa Cruz
Refinement
of Near-Surface P and S Velocities in the SCEC 3D Velocity Model
Using 3D Waveform Modeling
Mentor: Kim Olsen, UCSB
Active-source industry data were processed
using the tomographic velocity inversion method of Hole (1992)
to create three P wave velocity models at 50 m grid spacing for
the upper 500 m of crust in the Northridge epicentral region
of Southern California's San Fernando Valley (SFV) (Pattelena
et al., 1998). These profiles are named SFV-11, SFV-08, and SFV-12
(Fig. 1). Unusually slow P wave velocities were found along all
three profiles ranging from 900 to 2600 m/s (Fig's. 2 and 3).
Additionally, one of the three profiles, SFV-12, had S wave arrivals
with a resolution sufficient for an S wave velocity model at
50 m grid spacing for the upper 300 m of crust to be generated.
Unusually slow S wave velocities were found ranging from 300
to 900 m/s (Fig. 3). From this profile, we were able to calculate
Vp/Vs, finding a variable Poisson's ratio of 0.2 near the free
surface to greater than 0.4 throughout most of the model (Fig.
3). These high-resolution 2D models could provide a valuable
constraint on the SCEC 3D Velocity Model in the 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 define a Southern California Earthquake
Center (SCEC) summer internship project that will compare the
near-surface velocities in the tomographic profiles to those
in the SFV portion of the SCEC 3D Velocity Model, Version 2,
(SCEC 3D), as well as the ground motion response using the two
different models. The primary goal of these comparisons is to
outline any differences, and thereby potentially improve ground
motion estimates in the SFV. For the method of analysis we use
both 2D and 3D fourth-order staggered-grid visco-elastic finite-difference
modeling to generate synthetic wave propagation. We then compare
the accuracy of the seismic response in terms of amplitude of
the SCEC 3D and the tomographic models against data for Northridge
aftershock events. In addition, we constrain the anelastic attenuation
in the near-surface material by trial and
error of different Q values in the 3D model.
Kathryn van Roosendaal
CSU Northridge
SEISMIC
SLEUTHS: A Teacher's Package for Grades 7-12
Mentor: Bob De Groot
Seismic Sleuths was developed by the American
Geophysical Union (AGU) and the Federal Emergency Management
Agency (FEMA) in 1995 as an earthquake education curriculum for
grades 7 through 12. It is unique in that it includes the methods
of scientific investigation as well as the conclusions. The curriculum
also includes tools for students to prepare for earthquakes and
other natural disasters. The major topics included are: earth
science and paleoseismology, community officials involved with
disaster support, earthquake waves and the development of modern
seismology, the response of buildings and other structures to
earthquakes, and earthquake preparedness and safety.
In order to reflect advances made in earth
science, the National Science Foundation (NSF) funded the revision
of the Seismic Sleuths curriculum in 1999 under the direction
of the Southern California Earthquake Center (SCEC). For Seismic
Sleuths 2001, each of the major sections will be streamlined
and reorganized so that each may be used stand-alone if necessary.
Each laboratory activity will updated and redesigned if necessary.
Printed and video resources lists for each topic will also be
updated and expanded to include electronic sources. Finally,
the curriculum will be reevaluated in terms of the final 1995
version of the National Science Education Standards.
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