Paleoseismic Studies of the San Andreas Fault in the San Bernardino Area

Project Description: Dr. Sally McGill had logged an open trench across from the San Andreas Fault at Plunge Creek in the San Bernardino area. Dr. McGill found one prehistoric earthquake exposed within the trench. Each side of the trench has 2 vertical walls separated by a bench half way up. However, the prehistoric earthquake that is exposed in the trench is at the same stratigraphic level as the bench, which makes it hard to tell for sure exactly which sedimentary layer is the highest faulted. Some radiocarbon dates have been obtained on charcoal from many of the layers. However, we need to document stratigraphic relationships at the San Andreas Fault. The results will help us determine exactly which layers bracket the earthquake horizon and will enable us to better constrain the time of the earthquake. So far, the available dates of the earthquake from carbon is A.D. 1440 and A.D. 1670.
Intern(s): Safaa Dergham
Mentor(s):

Sally McGill, California State University, San Bernardino

Velocity Structure in the Los Angeles Basins from Tomographic Inversion of Active Source Data

Project Description: A major area of research for Group D during 1998 is the integration of basin and regional velocity models. This effort requires the compilation of and making compatible earth velocity structures at many different spatial resolutions and scales. Existing active source data already available can provide velocity information at different scales to contribute to this research goal. We define a SCEC summer internship project which will contribute velocity structure structure information on two scales. The analysis method for both scales is the same: tomographic velocity inversion of refraction phases in active-source data (e.g., Hole, 1992).
Intern(s): Tracy Pattelena
Mentor(s):

David Okaya, University of Southern California
Nikki Godfrey, Graduate student

Development of an Interface for 3-D Visualization of SCEC Earthquake Data on the World Wide Web

Project Description: Earthquakes and the distribution of earthquakes in space and time is fundamentally a 3-D problem. In order to properly understand and interpret the properties of an earthquake, you must be able to visualize earthquakes in 3-D. I propose to develop a web-based interface between the SCEC database of earthquake hypocenters and recently standardized 3-D visualization tools. This will include Java based tools with the ability to extract data from the SCEC data archive, display the data in a Virtual Reality Modeling Language (VRML) browser, and provide web-based interactive 3-D earthquake graphics for the SCEC earthquake web pages. Users of the SCEC web page will then be able to access earthquake hypocenter data in 3-D, control the viewing perspective, and produce time-based animation of the SCEC data. Previous attempts have been made to develop systems to view earthquake data in 3-D, but they are platform specific (e.g. Xmap 8, a UNIX based system developed by Dr. Jonathon Lees of Yale University). The system I propose will be developed from Java based tools, which are accessible in the latest versions of Netscape Communicator and Microsoft Internet Explorer. These tools will make three-dimensional aspects of the earthquake information available to anyone with access to the Internet.
Intern(s): Leland Green
Mentor(s):

Craig Nicholson, University of California, Santa Barbara

Understanding Ground Motion Variations at the Van Norman Dam Complex Site

Project Description: The Van Norman Dam Complex site in Los Angeles County was affected by strong ground motion during the 1994 Northridge earthquake. Large variation in ground motions occurred over very short distances. I propose to collect and analyze weak motion surficial seismic data from the site under the supervision of Dr. Jamison Steidl. This data will be compared with data taken during and immediately following the Northridge earthquake, as well as with data I plan to collect from existing boreholes at the site.
Intern(s): Javier Santillan
Mentor(s):

Jamison Steidl, University of California, Santa Barbara

Investigation of the Coupling Between Structures and Ground Vibrations and the Implications on Damping in Buildings

Project Description: The recording of induced vibrations on the roof of Millikin Library in locations over 10 km away from site has introduced an investigation of the coupling between the structure and the ground. The waves excite the periods of the building and the building then transfers those waves into the ground. This implies that the kinetic energy used to shake the building has been transformed into the kinetic energy of wave motion in the ground; therefore, the damping response of the building is not entirely due to friction or to other inelastic properties, but is in fact largely a result of the waves simply moving into the ground. It is crucial to determine the amount of damping which is a result of this transferal of vibrations. The vibrations which are currently going from the set source, through the building, and into the ground, could conceivably travel from some unspecified source, through the ground, and into the building, creating a hazard to those in the building. This research directly contributes to earthquake hazard mitigation. If the magnitude of the building damping due to waves transferred into the ground can be determined, appropriate modifications can be made in the design of buildings to account for this added damping response. This summer I will investigate this building-earth coupling to determine the amount of the damping response of buildings due to waves being propagated into the ground. Additionally, since the location, source, orientation, phase, and frequency of the vibration are all known, we can study the shallow seismic velocity structure throughout the San Gabriel Valley. A map of the amplitudes and phase velocities will be produced using the data collected throughout the summer.
Intern(s): Lisa Sarma
Mentor(s):

Tom Heaton, California Institute of Technology

Analysis of Azimuthal Variation in Amplitude Factors in Sherman Oaks During the Northridge Earthquake Aftershock Sequence

Project Description: This project will investigate the effects of the 1994 Northridge Earthquake, specifically the damage and possible seismic focusing experienced within Sherman Oaks. As many have discussed, there was a great difference in the extreme damage experienced in Sherman Oaks compared to the fairly minor damage in nearby Encino. As H. Liu, UCLA Ph.D. 1998, conjectured in "Path and Site Effects on the Localized Damage Caused by the 1994 Northridge Earthquake" there appears to be some form of azimuthal dependance of the possible focusing in Sherman Oaks. To investigate this further, the NEAR (Northridge Earthquake Aftershock Recording) data will be sorted and analyzed, investigating the possible effects of distance, depth of event, and surficial effects to explain the apparent azimuthal dependance. The project will specifically concern itself with the topography of the region. Topographic maps of the Santa Monica Mountains (SMM) will be studied and reformatted taking measurements with respect to the strike of the SMM. Also included in my summer research will be preparation for further study of hazard modeling, not only in the Sherman Oaks/Encino area, but also within Santa Monica--another region hit very hard by the 1994 Northridge earthquake. I will be working on the LARSE2 (The Los Angeles Region Seismic Experiment 2) project, deploying seismometers for the Passive Array portion of the experiment, throughout Topanga Canyon. Other possible work includes: work on the High Resolution Santa Monica Project, a project to study the tomography of Santa Monica by driving a vibra-seis truck in and around Santa Monica to get a better sense of the tomography of Santa Monica. Tasks would include: getting permissions from landowners and the city, as well as locating maps and helping design the route to be taken by the truck.
Intern(s): Justin Rubinstein
Mentor(s):

Paul Davis, University of California, Los Angeles

Folding and Faulting Along the San Andreas Fault, Palmdale, California; Implications for Simple Shear Mechanics and Education of the Public

Project Description: Palmdale, California, along the Antelope Valley freeway (state route 14), is the location of one of the best exposures of the San Andreas fault zone and its related structures. The fault zone consists of a set of faults that parallels the San Andreas fault (SAF) and commonly spans a width of several kilometers. A roadcut about 27 m high and about 300 m long exposes highly folded and faulted middle Pliocene lacustrine rocks (Anaverde Formation) within the fault zone. The Mojave segment of the SAF, along which the most recent rupture in 1857 occurred, crosses the highway at the southern end of the roadcut. The roadcut is aligned nearly perpendicular to the strike of the fault and can be considered to be a large "trench." North of and parallel to the SAF is the Little Rock fault which has had more than 20 km (Barrows 1987) of accumulated lateral slip. The Little Rock Fault is not exposed but is located a few meters north of the end of the roadcut. The "trench" allows a close look at the subsurface structure and deformation related to these two strike-slip faults. Drew (1976) described a tectonic history of the roadcut area: dextral shear, shortening, and uplift. In his discussion he suggested lateral displacement of a segment of the "trench" between two bounding faults and middle to late Pliocene folding, but he didn't describe any mechanism for faulting. Sieh, et al. (1992) suggested dextral warping and clockwise rotation of the fault zone along Pallett Creek approximately 20 km southeast of highway 14 and the "trench." The geometries related to the fault zone are local and may not be genetically linked. Thus, any interpretation of the geometry along the "trench" will be new and demonstrate the lateral change common in strike-slip tectonics. I think two right lateral strike-slip faults with exposed folds and faults between them lead one to consider the possibility of en echelon folds and fractures within this structurally complex area. Besides Drew (1976) and Barrows (1987), previous studies includes a stratigraphic section published by Wallace (1949) and the separation and mapping of the Anaverde Formation into eight members (Barrows, et. al. 1976, 1985) from Elizabeth Lake to Juniper Hills.
Intern(s): Lowell Kessel
Mentor(s):

Arthur Sylvester, University of California, Santa Barbara

Geomorphic Mapping and 3-He Chronology of Rock Slide Scarps Along the Oak Ridge Fault

Project Description: I intend to map rock slides scarps on the hanging wall of the Oak Ridge fault. I will attempt to establish the chronology of these scarps using the 3-He technique on interbedded basalts exposed on the scarps.
Intern(s): Jacquelin Moccand
Mentor(s):

Ann Blythe, University of Southern California