Reference Earthquake Digital Library -- Structure and Technology

Project Description: Understanding earthquake processes involves integration of a wide variety of data and models from seismology, geodesy, and geology. While the geophysics community has established data centers to archive and distribute data in standard formats, earthquake models lack a similar facility. This often dramatically reduces their lifespan, because the models lack sufficient documentation and file format information to render them useful. The objective of the Reference Earthquakes Digital Library is to create the infrastructure to preserve the models in a central facility and to extend their lifespan for use in other studies. A critical part of the digital library infrastructure for reference earthquakes is the ability for the modeling community to submit and update models. Additionally, the metadata and model data files must be checked to insure that they conform to the standards established for the digital library. I designed and implemented browser based submission and update interfaces by extending the digital library developed by the San Diego Supercomputer Center. The interfaces use a combination of JavaScript, Perl, PHP, Java, and C to process and validate the submission information. I also adapted the data retrieval interfaces for Reference Earthquake use. These interfaces are part of a fully functional prototype Reference Earthquakes Digital Library for the 1992 Landers and 2004 Parkfield earthquakes. The digital library provides curation and ready access to archived models in standard formats with associated metadata in a common, permanent repository.
Intern(s): Alexei Czeskis
Mentor(s):

Greg Beroza, Stanford University

Holocene Slip Rate of the San Andreas Fault at Plunge Creek, Highland, California

Project Description: In an effort to measure the Holocene slip rate of the San Andreas fault, we have continued field mapping and have conducted trenching at an offset channel in the East Highlands Ranch area of Highland. An abandoned channel of Plunge Creek is preserved on the southwestern (downstream) side of the fault. It is a remnant from a time when the channel flowed parallel to the fault in order to connect two channel segments that had been offset by slip on the San Andreas fault. The fault-parallel channel segment was abandoned when the channel re-incised straight across the fault. Since that time, the newly incised channel wall has also been offset by the San Andreas fault. On the northeast (upstream) side of the fault there are two major gravel-fill terraces preserved within the canyon of Plunge Creek. The channel wall that truncates the fault-parallel segment of the abandoned channel most likely correlates with the riser between the high and low terraces northeast of the fault. A preliminary estimate of the right-lateral offset of this feature is about 307 meters. Several trenches on the high and low terraces were excavated in November and December of 2004 for the purpose of collecting dateable material to constrain the age of the offset terrace riser. Fourteen charcoal samples have been submitted for radiocarbon dating and fifteen samples were collected for optically stimulated luminescence dating were collected. Samples for cosmogenic nuclide surface exposure dating were also collected from boulders on the high and low terraces. The pending dates and a more refined measurement of the offset will allow us to estimate the Holocene slip rate along this part of the San Andreas fault. The San Andreas and San Jacinto faults are the dominant faults within the plate boundary fault system in southern California. Together they accommodate about 70% of the Pacific-North America plate motion. However, there has been considerable debate as to whether the San Andreas fault contributes substantially more to the plate boundary deformation in southern California than the San Jacinto fault, whether the two faults contribute approximately equally or even whether the San Jacinto fault contributes more. The Holocene slip rate of the San Andreas fault, in Cajon Pass is well-documented at 24.5 +/- 3.5 mm/yr (Weldon and Sieh, 1985). However, some investigators suggest that the San Andreas fault slip rate decreases southeastward along the San Bernardino strand, as more and more slip is accommodated by the San Jacinto fault (Matti and others, 1992; Morton and Matti, 1993). Our work on measuring the Holocene slip rate of the San Andreas fault in Highland is aimed at testing this hypothesis.
Intern(s): Amanda Lopez
Mentor(s):

Sally McGill, California, State University, San Bernardino

Fault-Based Accelerating Moment Release Observations in Southern California

Project Description: Many large earthquakes are preceded by a regional increase in seismic energy release. This phenomenon, called “accelerating moment release”(AMR), is due primarily to an increase in the number of intermediate-size events in a region surrounding the mainshock. Bowman and King (GRL, 2001) and King and Bowman (JGR, 2003) have described a technique for calculating an approximate geologically-constrained loading model that can be used to define regions of AMR before a large earthquake. While this method has been used to search for AMR before large earthquakes in many locations, most of these observations are “postdictions” in the sense that the time, location, and magnitude of the main event were known and used as parameters in determining the region of precursory activity. With sufficient knowledge of the regional tectonics, it should be possible to estimate the likelihood of earthquake rupture scenarios by searching for AMR related to stress accumulation on specific faults. Here we show a preliminary attempt to use AMR to forecast strike-slip earthquakes on specific faults in southern California. We observe significant AMR associated with scenario events along the "Big Bend" section of the San Andreas fault, suggesting that this section of the fault is in the final stages of its loading cycle. Earthquake scenarios on the San Jacinto fault do not show significant AMR, with the exception of the "Anza Gap". No significant AMR is found associated with the Elsinore fault.
Intern(s): Lia Martinez
Mentor(s):

David Bowman, California State University, Fullerton

A Comparison of the Logging Methods for a Trench across the San Andreas Fault in the Carrizo Plain

Project Description: For my SCEC Internship I helped log two trenches across the San Andreas Fault at the Bidart Fan in the Carrizo Plain. The purpose of logging was to document evidence and ages of multiple surface ruptures from large earthquakes. I experimented with two methods of logging trench T5, with photo logs as well as hand logs, to compare which method is most useful for the Carrizo Plain. Due to the photography equipment used and characteristics of exposed materials, the hand logs conveyed a clearer picture of fault rupture. Since the Carrizo Plain sedimentation does not offer a variety of color, identifying evidence of rupture proved difficult with the photo logs. The hand logs were simpler because they had already been interpreted through drawings of the trench walls. Although this method is more subjective, the similar sedimentation of the bed layers renders the hand logs more valuable since it focuses the researcher to study the trench wall with a close eye. Using the best logging method for the Carrizo Plain is crucial since the logs are used to interpret the past behavior of the fault. Through this research, we hope to ascertain the best method for documenting past behavior of the San Andreas Fault in the Carrizo Plain.
Intern(s): Emily Starke
Mentor(s):

Lisa Grant Ludwig, University of California, Irvine

A Comprehensive 3-D Geophysical Model of the Crust in the Eastern Transverse Ranges

Project Description: The Eastern Transverse Ranges provides an ideal sampling location for crustal information because of the exposure of a variety of crustal layers from varying depths. The easternmost areas and the adjacent south central Mojave Desert expose upper crustal rocks, and rocks further to the west were exhumed from progressively deeper levels, nearly to the present day average Moho. Eastern areas of the ranges contain mostly volcanic, sedimentary, and granitic rocks. Western areas contain mostly granite, granodiorite, tonalite, and gneiss with no volcanic or sedimentary rocks. The variety of rock types and range of crustal depths allows detailed estimation of geophysical characteristics for a representative in situ southern California crustal column. This study is based on analyses of approximately 300 samples of basement rocks of the Eastern Transverse Ranges. P-wave velocity was calculated using Christensen and Mooney’s (1995) equation for velocity variation as a function of density and temperature (table below). P-wave velocity through these rock types varies with depth, pressure, and temperature. Velocities for average heat flow are listed only for regions where the rock occurs; a volcanic rock, like basalt, occurs only in the upper crust and will not have a middle crust velocity listed. Rock types occurring in both upper and middle crust, like granite, will have a velocity range listed for each depth region.

Rock Type Upper Crust Vp (km sec-1) Middle Crust Vp (km sec-1)
basalt	6.6 - 6.7
quartzite	5.8 – 6.2
granite	5.6 - 6.1 5.6 – 6.1
granodiorite	5.8 – 6.2 5.8 – 6.2
gneiss	5.7 – 6.9
amphibolite	6.8 - 7.6
tectonite	5.8 – 6.5
tonalite	6.2 – 6.5

Magnetic susceptibility was directly measured on hand specimens, and results follow two trends with increasing P-wave velocity. Generally, a positive correlation exists in the volcanic and granitic rocks, but no correlation is apparent for the metamorphic rocks. These velocity and magnetic susceptibility values, based on surface samples, will be used to make a depth-dependent geophysical model using GIS. Depth assignments for surface samples were derived from pressure estimates based on the aluminum content of amphiboles in selected granitic rocks. The resulting model range of velocities and magnetic susceptibilities at varying depths in the crust can be compared to models constructed from aeromagnetic and seismic data.
Intern(s): Sarah Needy
Mentor(s):

Andrew Barth, Indiana University

Dynamics of an Oblique-Branched Fault System

Project Description: We use a dynamic 3-D finite element analysis to investigate rupture propagation and slip partitioning on a branched oblique fault system. Oblique slip on a dipping basal fault propagates onto vertical and dipping faults near the Earth’s surface. When the slip on the basal fault includes a normal component, the preferred rupture propagation is upward to the vertical surface fault. Conversely, a thrust component of slip on the base fault results in preferred propagation upward to the dipping surface fault. We also find that oblique slip on the basal fault results in partitioned slip on the near-surface faults, with more strike-slip motion at the surface trace of the vertical fault, and more dip-slip motion at the surface trace of the dipping fault. This result is in agreement with the static predictions of Bowman et al. (2003). The results also indicate that the stress interactions that exist in geometrically complex fault systems can lead to complexity in rupture propagation, including a crucial dependence on the direction of slip.
Intern(s): Harmony Colella
Mentor(s):

David Oglesby, University of California, Riverside

Maya 3D Modeling and Animition for Scientific Visualization

Project Description: Exploring Fledermaus and concepts developed with LA3D and SCEC-Video with other visualization tools.
Intern(s): Jeremie Smith
Mentor(s):

Debi Kilb, University of California, San Diego

(no name)

Project Description: My project will focus on validating the Community Fault Model (CFM) in the LA Basin. The project is related to research done by Andrew Meigs and Michelle Cooke during the past couple of years. They are using geologic data and mechanical models to validate the Community Fault Model. I will generate maps of the base of a 2.9 Ma unit (Pico Formation) to map the location and amplitude of folds in the subsurface. Geological data will be compiled in a GIS. Wells for locating the depth of the Pico Formation will be input in the GIS, as will geologic map data in order to make a regional isopach map of the marker. Next I will take model uplift values and make a separate coverage of these results over the same geographic area as the surface and subsurface data coverages. From there I will use the GIS to develop an error estimation scheme to test misfit between data and models both at points of observation (wells, outcrops) and in regions where uplift values have been interpolated.
Intern(s): Della Graham
Mentor(s):

Andrew Meigs, Oregon State University

Loss Estimates for San Diego County Due to an Earthquake Along the Rose Canyon Fault

Project Description: A study was done to examine possible losses to San Diego County should a full-fault earthquake-rupture occur along the Rose Canyon fault, which runs directly through portions of San Diego and is evidenced by Mt. Soledad and the San Diego Bay. The total length of the fault is ~70 km (including the Silver Strand fault). Following the 2002 National Seismic Hazard Mapping Program, we consider a full fault rupture to be between magnitude 6.7 and 7.5, with the most likely magnitude being 7.0. Using this range of magnitudes, sampled at every 0.1 units, and six different attenuation relationships, 54 different shaking scenarios were computed using OpenSHA (www.OpenSHA.org). Loss estimates were made by importing each scenario into the FEMA program HAZUS-MH MR1. The total economic loss is estimated to be between $7.4 and $35 billion. The analysis also provides the following estimates: 109 – 2,514 fatalities, 8,067 – 76,908 displaced households, 2,157 – 20,395 in need of short term public shelter, and 2 - 13 million tons of debris generated. As in a previous study done on the effect of a Puente Hills earthquake in Los Angeles, this study shows the effect of attenuation relationship choice to have a greater effect on predicted ground motion then the choice of magnitude, thus leading to larger uncertainty in the loss estimates. A full fault rupture along the Rose Canyon fault zone would be a rare event, but due to the proximity of the fault to the City of San Diego, the possibility is worth consideration for possible mitigation efforts.
Intern(s): Loren Wimmer
Mentor(s):

Ned Field, United States Geological Survey, Pasadena

GPS Data Collection in the San Bernardino Mountains

Project Description: The objective of our project was to collect GPS data from the areas that surround the San Andreas and San Jacinto faults so that we could update the velocity vectors on a map of the area. Another major part of the data collection was to fill gaps in the San Bernardino mountain range by occupying stations that did not have previous data, starting a new data stream for future years. From June 21 to July 1, 2005 SCEC intern Adam Skalenakis and I participated in a two-week NSF-funded GPS campaign collecting data from twelve stations across the San Andreas and San Jacinto faults. We spent this time learning how to set up GPS equipment, collecting data and assisting 17 high school teachers, 13 undergraduates and 12 high school students with the same process. At each site for three to four days, eight hours of data was collected. After the campaign was over Adam and I went out to occupy eleven more stations in the San Bernardino Mountains in order to fill in gaps in SCEC’s Crustal Motion Model 3 (CMM3). At least 24 hours of continuous data was collected from each of these sites. After the data collection, my part of the project was to process the GPS data using Auto-GIPSY. Auto-GIPSY is a web-service supported by the Jet Propulsion Laboratory (JPL) that retrieves Rinex files from a server and processes them using JPL’s GIPSY software, which gave me the position of the station in terms of deviation from the nominal coordinates that were in the Rinex file. I then plotted the position as a function of time for each site and updated the velocity estimate for each site. I came across some complications when processing through Auto-GIPSY, but this was easily fixed by formatting the rinex file using TEQC, a program supplied by UNAVCO. I also went back to previous years and reprocessed data that did not process correctly the first time. After processing the data from the two-week campaign I processed and reprocessed about 70 files all together. From a total 221 data files that have been collected by the CSUSB-Harvey Mudd team since 2002, 82% have now been processed successfully. After three years of data collection the velocities are still somewhat uncertain. In particular 6106 has a velocity of about 11 cm/yr relative to North America. This is faster than the Pacific plate velocity of about 5 cm/yr and is thus unreasonable. The velocities of the remaining eleven stations seem more reasonable. Most of them are moving in a northwestern direction, 1.1 to 4.8 cm/yr, with the velocities generally increasing going southwestward on the Pacific plate. This is what would be expected for elastic strain accumulation along the San Andreas and San Jacinto faults. One-dimensional elastic modeling of our data suggests that the deformation is concentrated on and eastward of the San Andreas fault with relatively little deformation on the San Jacinto fault. However, because of the uncertainty of the velocities the results of the modeling are highly preliminary.
Intern(s): Adam Skalenakis
Mentor(s):

Sally McGill, California State University, San Bernardino

Creep Measurements and Depth of Slip Along the Superstition Hills Faults as Observed by InSAR

Project Description: Data from 65 ERS-1 and ERS-2 interferograms (descending, track 356, frame 2943) covering the Western Salton Trough and spanning a time period from 1992 to 2000 are used to measure surface deformation along the Superstition Hills fault. We model the near-fault (within 5 km) deformation along the Superstition Hills fault using a 2D analytic model of a vertical strike-slip fault. We assume all the observed signal is due to shallow slip (above the seismic zone). Using data from 4 cross-sectional profiles of interferograms across the fault, we find an average slip rate of 7.2 ± 2.1 mm extending to a depth of 3.6 ± 1.5 km. The lower bound of the shallow creep appears to increase to the northwest along the Superstition Hills fault.
Intern(s): Afton Van Zandt
Mentor(s):

Rob Mellors, San Diego State University