Data Collection and Analysis of Hector Mine Post-Seismic GPS Data

Project Description: After the October 16, 1999 M7.1 Hector Mine earthquake, there has been a focused effort on collecting postseismic deformation data. Within 48 hours of the quake, GPS receivers were set up around the fault. Since then, continuous GPS sites have been installed and repeated campaign GPS measurements have been made in the area surrounding the fault rupture. By measuring the postseismic deformation, we hope to capture the short-term after-slip and relaxation of the crust. Studying these phenomena will give us a better understanding of fault mechanics, the earthquake cycle, and the rheology of the crust. The project will involve data collection, data analysis and modeling. In June, we spend several days collecting campaign GPS measurements at sites on the marine base that are part of the SCEC Hector MIne postseismic network. The data collection will be done with Ashtech Z-12 GPS receivers, which will be set-up on each site for at least 24 hours. These observations will extend the time series for the postseismic network stations, last surveyed in April, 2000. The measurements, and data from continuous sites, will be analyzed using GIPSY-OASIS II software. The project plan is to complete the data analysis for all existing Hector Mine GPS data through mid-July, 2000. This work will include integrating campaign and continuous measurements mad since mid-March with the earlier data. Once the data have been collected and analyzed, we will model the results using simple dislocations in an elastic material. This type of modeling will allow us to see if there was any afterslip on or surrounding the coseismicinvert for the fault slip distribution that best fits the postseismic time series. We will also be able to determine if the data cannot be fit by afterslip alone, and requires models that include crustal relaxation.
Intern(s): Teresa Baker
Mentor(s):

Susan Owen, University of Southern California

Reconstruction of Trench Logs as a Test for Interpreted Paleosiesmic Events

Project Description: Accurate resolution of paleoseismic events in trench exposures requires the correct interpretation of observed stratigraphic and structural relationships. One method of testing the actual occurrence of interpreted events is to reconstruct the structural and sedimentological history of a trench exposure on an event by event basis. In this project, I will construct retrodeformed cross-sections for trench exposures for two currently active projects, one on the San Jacinto fault (Carrizo Wash) and one one on the San Andreas fault (Frazier Mountain). Trenches are currently open on the San Jacinto fault so I will begin with those interpreted sections. Furthermore, I have already been to the Carrizo site exposures and may be able to help with the final stages of data collection when this internship begins in June. The Frazier Mountain exposures are to be opened in late June and I will spend some time assisting with data recovery for that site. The majority of my effort will then be spent at SDSU doing the reconstructions. The overall goal is to construct a series of cross-sections that show the stratigraphy of the site prior to each surface rupture. If each interpreted event is real, then each reconstruction should produce a reasonable cross-section of the site prior that interpreted event. On the other hand, if an interpreted event cannot be reconstructed in a reasonable fashion, then we will investigate whether the mismatches are due to lateral slip or misinterpretation of the earthquake history. The end product will be a defendable sequence of reconstructions that show the earthquake history at each of these two sites on an event to event basis.
Intern(s): Natanya Black
Mentor(s):

Thomas Rockwell, San Diego State University

Mapping Small-Scale Crustal Deformation Using Paleomagnetic Vectors and GIS

Project Description: I will map detailed patterns of crustal deformation that have occurred in the western Transverse Ranges of southern California since Miocene time using GIS (ARC/Info and ArcView) and existing paleomagnetic, fault, and topographic data. Mapping of these data will help in determining locations of crustal rotations and whether they occurred by small or large crustal blocks. The mapping details will also indicate if rotations were accommodated by faults that are not known nor thought to be significant.
Intern(s): Marie Herrera Adsetts
Mentor(s):

Bruce Luyendyk, University of California, Santa Barbara

Comparison and Refinement of Southern California Seismic Hazard Analysis

Project Description: A study of seismic hazard analysis for the S. California region. Work would include review of existing probabilistic maps and articles, as well as comparison with scenario-based predictions of ground motion. If possible, I would like to include limiting data for ground motion, for instance toppling accelerations of precariously balanced rocks, gathered through investigative and forensic field work. This data might lead to revision of existing PSHA estimates.
Intern(s): Nathan Robison
Mentor(s):

John Anderson, UNR Seismology Laboratory

The Earthquake Hazard for the Rincon Creek Anticline (RCA) and the Associated Buried Reverse Fault, Carpinteria, CA.

Project Description: The main objective of the proposed internship is to evaluate the RCA and the associated buried reverse fault to gain a better understanding for the earthquake hazard this structure presents for the city of Carpinteria, CA. The RCA is a recently discovered structure associated with the Rincon Creek fault (Jackson and Yeats, 1982; Gurrola and others, 1998). The fold most likely represents a fault propagation structure that is rapidly propagating westward into the Carpinteria basin. The area is rapidly urbanizing and plans have been suggested for the construction of an elementary school across the structure near the western terminus of the fold. Detailed study of the growing anticline is necessary to determine the potential earthquake hazard of the buried Rincon Creek fault. The research plan is to carefully map the RCA, which apparently folds the 45 Ka marine terrace on the backlimb of the structure, and attempt to date the youngest material folded through the excavation of trenches. The proposed internship project is part of work being funded by SCEC and the National Science Foundation to better understand the earthquake hazard of the Santa Barbara Fold Belt and the processes related to active fold growth.
Reference: Gurrola, L. D., E. A. Keller, M. A. Trecker, R. D. Hartleb, and T. W. Dibblee, Jr., 1998, Active Folding and Buried Reverse Faulting, Santa Barbara Fold Belt, California,
In: Behl, R. J., ed., Cordilleran Section of the Geological Society of America, Guidebook to Field Trip #11, CSU Long Beach, Long Beach, CA. Jackson, P. A. and R. S. Yeats, 1982, Structural evolution of the Carpinteria basin, western Transverse Ranges,
California: The American Association of Petroleum Geologist Bulletin, vol. 66, no. 7, p. 805-829.
Intern(s): Adam Webber
Mentor(s):

Edward Keller, University of California, Santa Barbara

Paleoseismic Study of the San Andreas Fault Near San Bernardino

Project Description: This project will involve excavation and logging of a new trench across the San Andreas fault at the Plunge Creek site. Two students are applying for SCEC interships to work on this trench. If both are awarded internships, each student will work on one wall of the trench as her own project. Having two students working in the same trench has advantages in terms of safety.
Intern(s): Kelly Schmoker
Mentor(s):

Sally McGill, California State University, San Bernardino

Compile Updated Fault Maps of the Southern California Continental Borderland (Offshore Region) for the Master Model

Project Description:

• Tabulate fault attributes for incorporation into International Lithosphere Program Active Fault Database--complete ILP fault attribute forms.
• Write descriptive paragraphs for each major fault/fault zone to include on the SCEC data center web page.
• Compile Seismotectonic maps of the major faults/fault zones defining major fault segments and "characteristic" earthquake magnitudes.
• Complete digitization of fault maps into GIS format (Integraph Mapping Office; MapInfo) for World Wide Web publication.

Intern(s): Debra Einstein
Mentor(s):

Mark Legg, Legg Geophysical

Determining Activity of the Oceanside Detachment Offshore Southern California

Project Description: Increasing awareness of the hazards posed by blind thrust earthquakes in the Los Angeles Basin has led to recent studies aimed at defining regional thrust geometry and the recency of folding above these thrusts (Shaw and Suppe, 1995; Shaw and Shearer, 1999; Grant et al., in review; Oskin et al., in review). Mapping, age-dating, and structural analysis in the southern LA Basin (i.e. Orange County) has identified the San Joaquin Hills as a fault-related fold above an east-vergent blind thrust. Studies of seismic reflection data in adjacent offshore areas suggest that this thrust overlies a relict Miocene extensional feature, the Oceanside detachment. Preliminary mapping by Carlos Rivera and John Shaw at Harvard indicate compressive folding above the Oceanside detachment, suggesting it may be linked to the San Joaquin Hills blind thrust as part of an active west-vergent wedge- thrust structure. I propose to map the bathymetric expression of the wedge tip, as defined by the recent mapping of Rivera and Shaw, to define the style and recency of folding of late Quaternary marine sediments which are not imaged in the industry seismic data.
Intern(s): Grant Kier
Mentor(s):

Karl Mueller, University of Colorado, Boulder

Inversion of Teleseismic Receiver Functions via Evolutionary Programming

Project Description: I am currently working on a project that consists of developing a high performance implementation of a teleseismic receiver function modeling program. Dr. Steven Day is one of my two co-advisors; my other advisor is Professor Richard Frost, Mathematics and Computer Science, SDSU and Scientist at the San Diego Supercomputer Center (SDSC). This program was written by Charles Hoelzer a former student of Dr. Day's, following methods originally formulated by J.B. Minster and N. Williams of the University of California, San Diego. It explores the application of evolutionary programming combined with simulated annealing to the inversion of receiver function data to estimate the seismic velocity structure of the Earth's crust. My current project will reach a conclusion at the end of this semester that is of a first phase nature. This phase is a port of the code from Matlab into Fortran 90 targeting both single processor and multiprocessor Sun Computers. This code is being written as a single processor version but is employing coding techniques that will enable the Sun Fortran 90 optimizing compiler to generate very efficient executables for the different hosts. This project proposes to extend this effort by a further porting of the code to run on more powerful platforms and by refining some of the scientific techniques implemented in the original code. The revised code will then be tested using both synthetic data and real data from the Peninsular Ranges Batholith (PRB). The goal of this project is to further develop these techniques for generating valid velocity and depth models of the crust from the inversion of teleseismic receiver functions. The computationally intensive approach to nonlinear inversion explored in this project may also have future application to some of the more challenging 2D and 3D inversion problems of interest to SCEC. Teleseismic P waves that are incident upon a crustal boundary yield P to S wave conversions. By deconvolving the vertical component of a seismic signal the horizontal component, made up mostly of S wave conversions, can be isolated. This technique removes the obscuring effects of source function and instrument response allowing greater resolution at mid and lower crustal depths than standard reflective methods. These receiver functions can then be inverted producing a model of the shear velocity structure. These methods combined with other techniques such as seismic tomography can then be used to help better determine the structure of the crust.
Intern(s): Christopher Lynch
Mentor(s):

Steven Day, San Diego State University

Paleoseismic Investigation of the San Andreas Fault at Burro Flats

Project Description: The Burrow Flats site presents the possibility to gain a rich understanding of some of the past seismic activity along the San Andreas Fault. By examining a 200-foot long trench we will be able to interpret the last 2,000 years of history along the fault between San Bernardino and Indio. Burro Flats exhibits desired depositional and structural qualities that should accurately preserve the seismic record. These qualities include an active fault, a high rate of sediment deposition, a supply of carbon to determine the age of the sediment, and no human modification on local geology. We will focus on distinguishing several earthquakes. On a specific piece of the trench wall, I will examine and map the structural and stratigraphic information to distinguish the different earthquakes. My efforts will be part of a larger research project that intends to decipher the seismic activity in this specific region of the San Andreas Fault.
Intern(s): Ashley Streig
Mentor(s):

Kerry Sieh, California Institute of Technology
Doug Yule, California State University, Northridge

3-D Analysis of LARSE '94 Data

Project Description: The proposed internship project will contribute to Group D's goal for 1999 - that is, to construct at many scales the 3-D velocity structure of the LA region. The objective of this project is to obtain a three-dimensional velocity structure of the LA basin using the cross-strike LARSE'94 data. XXX project complements existing studies which are analyzing the two-dimensional transects of LARSE '94. The cross-strike data for this summer project has not yet been studied and will make full use of SCEC's LARSE'94 data sets. XXX project will have three stages:

1. an introduction to the LARSE data and UNIX computers (load the data onto the computer, learn seismic data processing software, plot the data),
2. learn about seismic wave propagation (identify seismic phases in the LARSE data and make travel-time picks),
3. learn and run arrival time tomography application software which produces 3D velocity structure.

The necessary LARSE data are inhouse at USC. The analysis software is already operational at USC. Direct supervision and instruction will be primarily by mentor Godfrey. This internship project will provide intern van Roosendaal with an opportunity to conduct geophysical research at a level beyond what is usually taught in undergraduate geophysics courses. However, advanced requirements are not necessary; intern van Roosendaal will be able to learn about the advanced seismology during the process of conducting the project research.
Intern(s): Kathryn Van Roosendaal
Mentor(s):

David Okaya, University of Southern California