Developing a Three-Dimensional Geophysical Model of the Crust in the Transverse Ranges of Southern California

Project Description: Improving models of crustal and upper mantle structure is necessary for understanding crustal architecture and how rifting processes influenced the development of lithospheric structure in southern California. The summer intern will use the petrology of basalts and mantle xenoliths from the southwestern Basin and Range and Salton Trough region to explore geophysical models of crust and lithosphere thickness and composition. The project will begin with field sampling in selected areas of the southwestern Basin and Range province in southern California. Following fieldwork, the intern will be responsible for carrying out petrography and laboratory measurements of rock and mineral compositions. The summer intern should have a background in petrology and/or geochemistry. This project will contribute to the SCEC Unified Structural Representation project in the development of a 3D model of Earth structure in southern California.
Intern(s): Heather DeWalt
Mentor(s):

Andrew Barth, Indiana University

Earthquake Ruptures on Rough Faults

Project Description: While faults are known to have irregular surfaces, almost all models begin with the assumption of perfect planarity. Slip between rough surfaces induces heterogeneous stress changes, in particular alterations of the normal stress that might lead to opening. Opening has been observed in the foam-rubber laboratory experiments of Brune and Anooshehpoor at UNR, and the resulting "chatter" between the fault walls during dynamic slip has been suggested to explain pulverized rocks observed near faults. Recent LIDAR measurements place constraints on the roughness spectrum of actual faults. The objective of this project is to explore the influence of fault topography on dynamic ruptures. A first step will be the development of a computational method to handle rough faults. The approach is to define a mesh (in "physical space") comprised of irregularly spaced cells that precisely tracks the fault surface. Next, a coordinate transformation is executed that maps the mesh from physical space to a regularly spaced Cartesian mesh in so-called "logical space." The governing equations (the elasticity equation off of the fault and the friction law on the fault) are likewise altered by the change of variables, but the permitted class of coordinate transformations ensures that the elasticity equation remains hyperbolic. The resulting equations are solved in logical space, either with finite-difference or finite-volume methods. Should we find that normal stresses do locally become tensile, then the process of fault opening will require a careful study. Here the focus will be poroelastic effects, since opening between two fluid-infiltrated solids presumably induces a suction that will draw fluid out of the rock matrix and into the opening between the fault walls. Once this void fills with fluid, then abrupt closure is rendered more difficult. A coupled fluid-poroelastic solid problem can be defined to address these issues, and any results incorporated into our models. The project requires knowledge of multivariable calculus, partial differential equations, and linear algebra, and of beginning college-level physics at a level appropriate for physics concentrators. The study will be supervised on a day-by-day basis by Dr. Eric M. Dunham, now Reginald A. Daly Postdoctoral Fellow in the Department of Earth and Planetary Sciences at Harvard, and will have overall supervision by Prof James R. Rice, a member of that same department.
Intern(s): David Belanger
Mentor(s):

Eric Dunham, Stanford University
James Rice, Harvard University

Damage Zone Structure Along the Calico Fault

Project Description: Fault damage zones are an active area of study intrinsic to our knowledge of earthquake nucleation and propagation. Recent InSAR and seismic studies highlight the complex nature of these damage zones and much is still unknown about their three-dimensional structure and evolution through time. To that end, seismic data were collected along the Calico fault in the eastern California shear zone from June to November, 2006, in a collaborative effort by scientists from several southern California universities. The SCEC/SURE intern will be responsible for picking seismic arrivals from the 6 month long data set of local, regional, and teleseismic earthquakes. These travel-time picks will then be used in a tomographic inversion to determine the 3D structure of the damage zone along the Calico fault. The intern is expected to have working knowledge of UNIX, a willingness to learn seismic analysis software, and knowledge of programming. Knowledge of Fortran is preferred, but any programming will be helpful.
Intern(s): Naomi Brown
Mentor(s):

Elizabeth Cochran, University of California, Riverside

Velocity Contrast Along the Hayward Fault From Analysis of Fault Zone Head Waves

Project Description:
Intern(s): Summer Ohlendorf
Mentor(s):

Zhigang Peng, Georgia Institute of Technology

Using Precariously Balanced Rocks to Place Constraints on Ground Shaking Along the Southern San Andreas Fault

Project Description: Precariously balanced rocks, common throughout the desert southwest, and near the San Andreas Fault, can place constraints on the ground shaking (important in designing buildings to resist earthquakes) caused by earthquakes that occur along the southern San Andreas Fault. The project will involve sample detection and possibly analysis to determine the length of time that these rocks have been precariously balanced; and help in constucting a GIS database. If you have taken a basic geology course, such as Natural Hazards or Introduction to Geology, feel comfortable with computers, and are able to work without much daily direction, this may be the summer project for you.
Intern(s): Deborah Weiser
Mentor(s):

Lisa Grant Ludwig, University of California, Irvine

Paleoseismology of Main Frontal Thrust, Nepal

Project Description: This research focuses on results from a trench site in far-western Nepal that has unearthed possible evidence of the Great June 6, 1505 earthquake, the largest earthquake to affect the Himalaya in the past 500 years. A SCEC intern would assist Dr. Doug Yule and his graduate students in their ongoing interpretation of the results from field work completed in the Fall of 2005 and 2006. Tasks would include (1) learning pertinent GIS to compile a 3D image of the trench site, (2) completing photomosaics of photographs taken of the trench walls, (3) researching the historic record from 1505 in northern India and southern Tibet, and (4) interpreting the geologic evidence from the trench site for this massive earthquake. The ideal intern would have some experience with GIS and would have taken courses in structural geology and stratigraphy and sedimentation.
Intern(s): Nick Rousseau, Kandace Kelley, Jessica Hinojosa
Mentor(s):

Doug Yule, California State University, Northridge

Defining Holocene Activity of the Compton Blind-Thrust Fault, Los Angeles Basin, California

Project Description: One of the most exciting recent developments in seismic hazard assessment in Southern California has been the recognition of several large blind thrust faults directly beneath metropolitan Los Angeles. One of these blind thrust faults, the Compton thrust fault, was originally identified by Shaw and Suppe (1996). This large fault extends northwest-southeast for 40 km along the western edge of the Los Angeles basin. Seismic reflection data define a growth fault-bend fold associated with the base of the thrust ramp and, along with well data, reveal compelling evidence for its Pliocene and Pleistocene activity (Shaw and Suppe, 1996), but its current state of activity has been the subject of intense debate within the SCEC community. We recently used SCEC funds to acquire new, high-resolution seismic reflection profiles across the upward projection of the locus of folding above the base of the blind thrust ramp. These new observations demonstrate that the folding observed on oil industry profiles extends upwards to depths of less than 21 m, suggesting that this large fault is active and capable of generating destructive earthquakes directly beneath metropolitan Los Angeles. In this study we will collect basic information to determine the recent slip rate of the fault, displacements and ages of ancient earthquakes generated by the Compton thrust. In order to do this we will acquire a transect of eight, 25-35-m-deep, continuously cored boreholes drilled directly into the high-resolution seismic reflection profiles. Continuous cores collected during the drilling will allow us to correlate strata between boreholes as well as to collect detrital charcoal and organic-rich sedimentary layers for radiocarbon dating. The SCEC intern will be involved in all aspects of data acquisition, including the siting of boreholes, logging of cores, preparation of stratigraphic cross-sections, collection of carbon for dating, and surveying the field area. A student with some knowledge of sedimentology and structural geology would be preferred.
Intern(s): Stephanie Tsang
Mentor(s):

James Dolan, University of Southern California

Testing the Earthquake Clustering Hypothesis for the Eastern California Shear Zone with Paleo-Earthquake Ages and Displacements on the Calico Fault

Project Description: Synthesis of paleoseismic data from the central Mojave Desert portion of the Eastern California shear zone (ECSZ) supports that notion that earthquakes recur in clusters across this portion of the southern California fault system (Rockwell et al. 2000). The Calico fault is the longest and fastest-slipping dextral fault within the Mojave ECSZ (Oskin et al. 2006a, 2006b) and thus presents an ideal candidate to test the strength of the earthquake clustering hypothesis. The fault is embedded between the traces of the 1992 Landers and 1999 Hector Mine earthquake ruptures and centrally is located within the portion of the Mojave ECSZ where clustering was documented by Rockwell et al. (2000). Nothing is known about the rupture history of the Calico fault. In this study we will document the paleoseismicity of the Calico fault to test its behavior within the context of regional earthquake clusters identified by Rockwell et al. (2000). This effort will test three alternative hypotheses for the relationship of regional earthquake clusters to the rupture history of the Calico fault:

• The timing of rupture events on the Calico fault is strongly modulated by regional earthquake clusters. Faster slip on the Calico fault is accommodated by either (a) larger earthquakes or (b) multiple events during each clustering period.
• The timing of rupture events on the Calico fault is weakly modulated by regional earthquake clusters. Earthquakes occur on the Calico fault during each clustering period, but additional earthquakes occur between these periods.
• The timing of rupture events on the Calico fault is not modulated by regional earthquake clusters. There is no statistically significant higher probability that earthquakes occurred on the Calico fault during regional earthquake clustering periods.

In this study we will collect basic information to determine the ages and displacements of Holocene earthquakes generated by the Calico fault. We will excavate a series of paleoseismologic trenches across the fault trace along a dry lake bed east of Barstow, California. In addition to detailed mapping of the playa stratigraphy and fault-related structures formed during ancient earthquakes, we will collect both charcoal samples for radiocarbon samples and samples for optically stimulated luminescence (OSL) dating. The SCEC intern will be involved in all aspects of data acquisition, including the siting, excavation, and mapping of trenches, collection of geochronologic samples, surveying the field area, and mapping nearby portions of the fault trace to determine recent geomorphic offsets along the Calico fault (i.e., "real" field geology! :-). A student with some knowledge of structural geology and sedimentology would be preferred.
Intern(s): Austin Elliott
Mentor(s):

James Dolan, University of Southern California

Dynamic Models of Earthquakes and Tsunamis

Project Description: For a 2007 Summer Undergraduate Research Experience project, I propose to investigate how the earthquake process affects the generation and propagation of tsunamis. We will construct and run computer models of tsunamigenic earthquakes and then use these models as inputs to computerized tsunami models. We will study how the geometry of the fault and the distribution of stress and frictional properties on the fault affect both the generation of tsunamis and the run-up of the tsunami on nearby land. The results will have implications for tsunami hazard in Southern California and worldwide. The successful intern will have some prior experience in programming and a basic knowledge of physics, although prior experience in numerical modeling is not necessary. The intern will aid in the setup of numerical models, and will take the lead in running these models and visualizing the results. We expect the results to culminate in a poster at the 2007 SCEC Annual Meeting, and then a peer-reviewed research paper. Research will take place at UC Riverside, with a possible short trip up to the USGS, Menlo Park.
Intern(s): James Wendt
Mentor(s):

David Oglesby, University of California, Riverside

A Tests of Two Earthquake Modeling Methods

Project Description: For a 2007 Summer Undergraduate Research Experience project, we propose to compare properties of earthquake ruptures generated by two very different computer codes. The first is a finite element method which solves the fully dynamic equations of motion on the fault and in the surrounding medium. The second is a quasi-static model in which displacement on faults is resisted by friction described by laboratory-derived rate-and-state-dependent constitutive relations. The latter model is mostly aimed at capturing the long-term interactions between earthquakes on different faults, and so the dynamic portion of the rupture process is modeled crudely with a fixed seismic slip velocity (whose magnitude is determined by simple radiation damping arguments). Partly because of this approximation, the quasi-static model takes several orders of magnitude less computer time to simulate a large earthquake than does the fully dynamic model. However, the quasi-static model does produce rupture scenarios that are, in many ways, reasonable. We will investigate how various elements of the models (e.g. pre-existing stress state, fault geometry) affect various aspects of the simulated ruptures (e.g. rupture velocity, ability to propagate past geometric complexities such as bends and stepovers) in both models to assess to what extent the simpler, faster quasi-static model captures the physics of the fully dynamic one. The successful intern will have some prior experience in programming and a basic knowledge of physics, although prior experience in numerical modeling is not necessary. The intern will aid in the setup of numerical models, and will take the lead in running these models and visualizing the results. We expect the results to culminate in a poster at the 2007 SCEC Annual Meeting, and then a peer-reviewed research paper. Research will take place at UC Riverside.
Intern(s): Christine Burrill
Mentor(s):

David Oglesby, University of California, Riverside
James Dieterich, University of California, Riverside

Investigations of the Superstition Hills Fault

Project Description: My main objective during this internship was to search locally recorded seismic data for micro-earthquakes and tremor on the Superstition Hills Fault, California. I first spent a few weeks gaining familiarity with the mapping and seismic analysis software packages Generic Mapping Tools (GMT), Antelope, and Seismic Analysis Code (SAC). I then created an Antelope database of seismic data collected during an on-going temporary deployment of seven Portable Broadband Instrument Center (PBIC) stations along the Superstition Hills Fault. After analyzing this data I have identified ~250 events which were not in the SCEC or ANSS catalogs, but most have P-S wave times of 3-6 seconds indicating they are too far away to be on the Superstition Hills Fault. Only ~5 of these events had the appropriate P-S wave times to be on the Superstition Hills Fault, and only ~10 tremor-like events were identified. The Superstition Hills Fault does not appear to be a highly seismogenic fault, but it is possible that future analysis of the data in this on-going project will find enough micro-earthquake and tremor events to find a meaningful correlation between the two.
Intern(s): Alexander Hanna
Mentor(s):

Elizabeth Cochran, University of California, Riverside

The International Earthquakes and Mega Cities Initiative

Project Description: Los Angeles is only one city in the world which is affected by major natural disasters. Though the City of Los Angeles is different from other cities because it is one of the biggest cities in the United States with a population that surpasses 3 million. Though it is not much different from other global cities in regards to population size. Many global cities have a shared identity in disasters, rather natural or manmade. It is imperative for cities around the globe to be able to learn from what other nations or large cities have done when it comes to preparing for a natural disaster. The idea that all cities can learn from others strengths or weaknesses when it comes to a disaster is effective on any scale.
Intern(s): Steven Johnson
Mentor(s):

Mark Benthien, University of Southern California

Multi-Hazards Demonstration Project: It's Your Fault... Prepare Now!

Project Description: The Southern California Earthquake Center/Summer Undergraduate Research Experience (SCEC/SURE) internship program unites students with the world's preeminent earthquake scientists and specialists. Though most interns still work one-on-one with a mentor, the SURE program has done something different this summer. SCEC/SURE gathered a group of four interns Eugenia Hyung, Stephanie Kelly, Robert Leeper III and Rosie Santilena to work with internship mentor Dr. Lucile Jones of the United States Geological Survey (USGS) on Southern California's section of the USGS's Multi-hazards Demonstration Project. A scenario is being created that combines the latest knowledge about Southern California's natural hazards, specifically earthquakes; with the impact they have on the physical, social, and economic fabric of our society. The interns' task for the scenario was to act as an interface between the scientific communities and the general public, interpret Southern California Geologic map data, find innovative ways to communicate the project's results to various audiences, and collaborate with the different project leaders to create a cohesive scenario. As a member of the Multi-Hazards Demonstration Project for my 2007 SCEC/SURE internship, I was presented with exciting challenges and exposed to cutting edge Earth Science. I interpreted geologic map data to determine the susceptibility to landslides and liquefaction that certain areas of southern California will face in our M7.8 scenario earthquake. The data was input into ArcGis and will soon be processed by FEMA's "HAZUS" risk assessment software for use in the scenario. I also wrote narratives that blend the science of the M7.8 scenario earthquake with the lives of characters chosen to represent southern California's population and describe how the earthquake affected them.
Intern(s): Rose Santilena, Robert J Leeper III, Eugenia Hyung, Stephanie Kelly
Mentor(s):

Lucile Jones, California Institute of Technology

Paleoseismic Investigation of the San Andreas Fault at Frazier Mountain, California

Project Description: We investigated a paleoseismic site on Frazier Mountain, near Frazier Park, California, on the Northern Big Bend section of the San Andreas fault. We cut a 60 m long, 3-4 m deep trench on the site of the Lindvall et al. (2002) trench, beginning at the base of the northern scarp and extending south across a late Holocene fan. The trench walls were cleaned, gridded into 1 x 0.5 m sections, photographed, and logged in the field at a scale of 1:7 or 1:12. Silt, sand, and gravel are interfingered in the trench. The stratigraphy indicates that the primary source of sediment is the late Holocene fan to the northwest, carrying sand and gravel sourced from the Precambrian gneiss of Frazier Mountain. A smaller volume of sediment is shed off the slope that forms the southern slope of the site and is composed of the Hungry Valley Formation. Numerous faults run through these deposits, presenting evidence for episodic earthquake recurrence. Using field logs, I will determine the source of each sedimentary package in the southern portion of the trench in order to understand the relative contributions of each sediment source and to build a sedimentary history of the site.
Intern(s): Helen Sheridan
Mentor(s):

Kate Scharer, Appalachian State University

Basin Data Collection for Post-Fire Debris Flow Analysis for Southern California

Project Description: The USGS Landslide Hazards Team is tasked with identifying the conditions that can lead to debris flows from recently burned basins in southern California. A database of information on rainfall, basin conditions and storm response was compiled for this analysis from a variety of sources, including rain gages, field studies, digital elevation models (DEMs), burn severity mapping and soil databases. One of the challenges of this project was identifying the best source of data to quantify the morphologic condition of the study basins. ARCGis was the main program used to gather this information, however it could not provide use with all of the data we needed. For this project, we explored the use of three supplemental programs that provide different measures of gradient distributions within a basin and of drainage structure to identify the most useful suite of potential variables and to assess relative ease of use. We evaluated the public domain databases of StreamStats and EDNA (Elevation Derivatives for National Applications) and the privately-marketed Rivertools. Streamstats is a web based program that can provide measures of basin area, gradient, drainage area, rock type, available water content, and many other useful basin and stream flow characteristics derived from 30-m DEMs. Unfortunately, the data is not presently complete for the state of California. Test maps were created evaluate the practical application of Streamstats. The program was easy to access and the information gathered was useful. However the basin delineation tool was imprecise and hard to manually edit. This caused problems with the accuracy of the data because the outlines of the delineated basins did not match those needed. EDNA also provides access to similar hydrologic and slope data, and can be based on either a 10-m or 30-m DEM. EDNA was very difficult to use and navigate. It took a long time to figure out how, but eventually maps were created. Unfortunately there was no way to gather any values from them without approval to access internal files by the administrators of the program. Overall, this process was slow and did not turn out desirable results. Rivertools is used to identify watersheds and drainage pathways within basins. Importing a DEM is very easy and any resolution can be imported, once done there is a plethora of information available, including different measures of area, slope, drainage density, and bifurcation ratio. Due to its ease of use and the variety of available information, I believe Rivertools is a good resource for data compilation for this study. By using both ARCGis and Rivertools we were able to successfully create a complete database that can be used for analyzing debris flow hazards in the southern California area.
Intern(s): James Hiller
Mentor(s):

Rainfall Intensity-Duration Thresholds for Debris Flows in Post-Burn Areas of Southern California

Project Description: Previous studies of debris-flow hazards within Southern California have demonstrated that wildfires increase the risk of debris flows in the affected basins. However, the exact relationship between post-burn precipitation and the generation of debris flows is still under investigation. My research this summer has focused on defining thresholds for rainfall intensity-duration conditions that can trigger life and property-threatening debris flows from recently burned basins in Southern California, and to verify existing thresholds. To record the winter storms that impacted areas burned during the summers of 2003-2005, the USGS established rain gage networks in drainage basins within Ventura, San Bernardino, and San Diego Counties. The response of each basin (debris flow, proto-debris flow, flood, or no response) to individual storms was also documented. For this study, proto-debris flow refers to a small, localized debris-flow event that does not coalesce to occupy an extensive drainage network (as a life- or property- threatening event would). For each storm of interest, we calculated the peak precipitation intensity for 10-minute, 15-minute, 30-minute, 1-hour, 3-hour and 6-hour durations (keeping intensity intervals suitable to storm length), and examined this data to identify the threshold conditions unique to the debris flow and proto-debris flow producing storms. Rainfall and response data from the Day, Gorman, School and Topanga Fires in Ventura County, the Harvard, Thurman, Blaisdell, Grand Prix, Old, Soboba and Mill Creek/Emerald Fires in San Bernardino County, and the Horse Fire in San Diego County, revealed that measures of rainfall intensity and duration can clearly define the threshold conditions at which debris flows are produced in each recently burned region. The existing threshold for the San Bernardino Mountains was verified using data from the Thurman Fire, where a debris flow was produced in response to rainfall intensities and durations greater than the previously-defined threshold for the area. Data from the Harvard Fire debris flows also verified the San Bernardino debris flow threshold even though the events affecting the Harvard burn area were short convective thunderstorms, unlike the longer winter storms evaluated in San Bernardino and San Diego. In Ventura County, the previously-defined debris flow threshold and a threshold for proto-debris flow activity, defined using data from the Day Fire, are a convincing distance apart, and the storm conditions that produced both debris flows and proto-debris flows were higher than those which showed no response. Data from the School Fire in coastal Ventura County verified the pre-existing Ventura County Threshold. This indicates within the same county, coastal and inland zones can be considered together when determining debris flow thresholds. The Horse Fire basins were the only burn regions which experienced no response to the documented storms. Therefore, a lower threshold line for San Diego County was established using the peak precipitation of non-event storms. All of these thresholds can be considered as realistic guidelines for predicting the likelihood of debris-flow events in a rudimentary warning system, and will be incorporated into the existing USGS/NWS Early Warning System for Debris Flows from Recently Burned Areas in Southern California.
Intern(s): Lindsay Leone
Mentor(s):

Economic Preparations

Project Description: I participated in a 10-week internship program called the Summer Undergraduate Research Experience, working for a USGS project led by economist Rich Bernknopf. I compiled and analyzed information about short term and long term economic consequences of a magnitude 7.8 earthquake along the San Andreas Fault in Southern California. The ultimate goal of the project is to use scientific information to stimulate policy-making regarding damage mitigation, preparedness, and resiliency. I spearheaded a questionnaire sent to SoCalFirst, a financial institution consortium, seeking feedback on expected consequences in the financial sector. I gathered baseline economic data for eight counties, including population, unemployment, employment by industry classification, wages, and worker commute modes and patterns over the past few years. I compiled the information into Microsoft Excel spreadsheets and analyzed recent trends. I researched the movement of goods in Southern California, with emphasis on the ports including the viability of alternative options if the ports and/or trucking routes are damaged in a quake. I studied business recovery following previous quakes to determine the factors that most influence a firm's ability to recover. I digested the relevant policies and regulations and economic information from the Palm Springs comprehensive plan.
Intern(s): Corwin Abbott
Mentor(s):

Rich Bernknopf, United States Geological Survey

A MATLAB Program to Measure the Fractal Dimension of Seismicity with Application to Southern California

Project Description: The fractal dimension of earthquakes epicenters in southern California is measured using a box-counting algorithm. A MATLAB program has been written that finds the minimum number of boxes in a grid that are required to “cover” the seismicity for a range of box sizes. The slope of a plot of the logarithm of the minimum box number as a function of the logarithm of the box length gives the fractal dimension. We investigate the variation of fractal dimension between different tectonic areas, and whether modern relocated catalogs yield fluctuations in slope that can be related to the structure of the regional fault network.
Intern(s): Brian Boyce
Mentor(s):

Aaron Kositsky, University of Southern California