Seismogenic, Electrically Conductive, and Fluid Zones at Continental

George R. Jiracek, Victor M. Gonzalez, T. Grant Caldwell,
Philip E. Wannamaker, and Debi Kilb

We explore the idea that fluid occurrence below the seismogenic zone plays an active role in the rupture process by examining how fluids spatially relate to seismicity at three continental plate boundaries: South Island of New Zealand, the Himalaya, and San Andreas fault, USA. With this objective, we project earthquake hypocenters onto magnetotelluric (MT) electrical resistivity cross-sections. MT detection of conductive zones in the crust containing low fractions of fluids (less than 1%) requires an interconnected network of fluid-filled porosity facilitated by shearing, fracturing, and/or grain-edge wetting. Mechanisms promoting fluid reservoirs in the ductile crust include: 1) stalling of upward propagating porosity waves, 2) tectonically induced neutral buoyancy, and 3) development of ductile shear zones. Distinct conductive horizons are detected at depth in the ductile crust in New Zealand and the Himalaya where the tectonic convergence is high. In the Parkfield segment of the San Andreas fault, where convergence is low, there is high conductivity in the ductile crust but it forms a sub-vertical corridor to the surface with no distinct top. The tops of sub-horizontal conductive zones are ~20 km depth in New Zealand and ~25–40 km in the Himalaya where the seismogenic crust extends only to 12 and 25 km depth, respectively. The deep conductive layer in New Zealand may have originated as a “water sill” facilitating water-weakening, localized deformation, and eventually becoming a water-rich, anisotropic, mylonized, ductile shear zone. Fluid exchange through the active Alpine fault may initiate or be initiated by fault rupture. Localized, unstable flow in deep fluidized zones detected by MT may trigger earthquakes above.

Jiracek, G. R., Gonzalez, V. M., Caldwell, T. G., Wannamaker, P. E., and Kilb, D., 2007, Seismogenic, electrically conductive, and fluid zones at continental plate boundaries in New Zealand, Himalaya, and California, USA: in D. Okaya, T. Stern, and F. Davey, eds., A continental plate boundary: Tectonics at South Island, New Zealand, Geophys. Mono. Ser. 175, AGU., Washington, DC, 347-369.


A Continental Plate Boundary: Tectonics at South Island, New Zealand

David Okaya, Tim Stern, Fred Davey, Editors

A Continental Plate Boundary offers in one place the most comprehensive, up-to-date knowledge for researchers and students to learn about the tectonics and plate dynamics of the Pacific-Australian continental plate boundary in South Island and about the application of modern geological and geophysical methods. It examines what happens when convergence and translation occur at a plate boundary by

• describing the geological and geophysical signature of a continental transform fault;

• identifying the diverse vertical and lateral patterns of deformation at the plate boundary;

• assessing an apparent seismicity gap on the plate boundary fault and fast-moving plate motions;

• comparing this plate boundary to other global convergent continental strike-slip plate boundaries;

• documenting the utility of the double-sided onshore–offshore seismic method for exploration of a narrow continental island; and

• Providing additional papers presenting previously unpublished results.

This volume will prove invaluable for seismologists, tectonophysicists, geodesists and potential-field geophysicists, geologists, geodynamicists, and students of the deformation of tectonic plates.

Geophysical Monograph Series, Volume 175, 350 pages, hardbound, 2007, ISBN: 978-0-87590-440-5, AGU Code GM1754405

Dr. Gary Peterson - National Geographic Consultant

Dr. Gary Peterson, expert on North American stratigraphy, provides his knowledge as a Science Consultant for the National Geographic’s new giant-screen film SEA MONSTERS: A Prehistoric Adventure. This film submerges audiences in an 80-million-year-old scientific mystery. Produced by National Geographic, narrated by Tony Award-winning actor Liev Schreiber and featuring original music by Peter Gabriel, SEA MONSTERS: A Prehistoric Adventure brings to life the most bizarre, ferocious and fascinating creatures to ever inhabit Earth’s oceans. From the giraffe-necked Styxosaurus and 20-foot “bulldog” fish Xiphactinus to the T-Rex of the ocean — the 40-foot super-predator Tylosaurus — these wondrous beasts defy imagination. The film combines dynamic, state-of-the-art animation with exciting paleontological discoveries around the world to take audiences on a remarkable journey into the unexplored world of ocean reptiles that lived during Earth’s Cretaceous Period. Now playing at the Reuben H. Fleet Science Center IMAX® Dome Theater

New Publication - Barry Hanan

Yellowstone plume–continental lithosphere interaction beneath the Snake River Plain

Barry B. Hanan1, John W. Shervais2, and Scott K. Vetter3

1. Department of Geological Sciences, San Diego State University, San Diego, California 92182-1020, USA,

2. Department of Geology, Utah State University, Logan, Utah 84322-4505, USA,

3. Department of Geology, Centenary College, Shreveport, Louisiana 71134, USA

ABSTRACT
The Snake River Plain represents 17 m.y. of volcanic activity that took place as the North American continent migrated over a relatively fixed magma source, or hotspot. The identification of a clear seismic image of a plume beneath Yellowstone is compelling evidence that the Miocene to recent volcanism associated with the Columbia Plateau, Oregon High Lava Plains, Snake River Plain, Northern Nevada Rift and Yellowstone Plateau represents a single magmatic system related to a mantle plume. A remaining enigma is, why do radiogenic isotope signatures from basalts erupted over the Mesozoic–Paleozoic accreted terrains suggest a plume source while basalts erupted across the Proterozoic–Archean craton margin indicate an ancient subcontinental mantle lithosphere source? We show that ancient cratonic lithosphere like that of the Wyoming province superimposes its inherent isotopic composition on sublithospheric plume and/or asthenospheric melts. The results show that Yellowstone plume could have a radiogenic isotope composition similar to the mantle source of the early Columbia River Basalt Group and that the plume source composition has persisted to the present day.

Hanan BB, Shervais JW, Vetter SK (2008) Yellowstone plume–continental lithosphere interaction beneath the Snake River Plain. Geology: Vol. 36, No. 1 pp. 51–54

2007 Honored Alumnus - Gary Peterson

2007 Honored Alumnus

Gary Peterson

The SDSU Geology Alumni Association and the Department of Geological Sciences are pleased to announce that Dr. Gary L. Peterson will be the recipient of the Baylor Brooks Honored Alumni Award at the annual banquet, tentatively scheduled for Feb 22, 2008. Dr. Peterson is very deserving as he has influenced more than 44 years worth of SDSU geology students (now alumni!). Congratulations, Gary!

December Crossword Puzzle - Meteorites

Java Interactive Puzzle


Printable Puzzle (pdf)

Fall 2007 Thesis Defenses

Hydrological investigations of the Santo Domingo Basin, New Mexico using electromagnetic soundings

Josh Woodworth

Friday, December 7th - CSL 422, 9:00am
Advisor - Dr. George Jiracek
B.S. Geological Sciences

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Testing the application and precision of optically stimulated luminescence on dating lacustrine shorelines in the Imperial Valley, southern California

Caitlin Lippincott

Friday, December 7th - CSL 422, 10:00am
Advisor - Dr. Tom Rockwell
M.S. Geological Sciences

Radiocarbon dating has proved ineffective to precisely date the timing of the last lake Cahuilla highstand. In contrast, Optically Stimulated Luminescence (OSL)
dating is an evolving technique with a different set of limitations and this method has demonstrated results with high precision that may allow for dating of deposits in this problematic period. Numerous explorers trekked through southern California beginning in the mid 1500’s. Diaries and maps were used in this study to further determine when a lake Cahuilla might have been present, mostly notably those of Father Kino in the late 1600 early 1700 and de Anza expeditions in 1774-1776. This study employs the use of OSL to try to precisely date the age of deposition of lake berms, fluvial sands and lake sands to better constrain the timing of the last Lake Cahuilla highstand. The initial OSL results show that there may be a significant partial bleaching problem with some samples.

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Geochemistry and U/Pb geochronology of the eastern-most Peninsular Ranges batholith of southern California and northern Baja California; implications for magmatism and tectonics at the onset of the Laramide orogeny

Rob Moniz

Friday, December 7th - CSL 422, 11:00am
Advisor - Dr. Dave Kimbrough
M.S. Geological Sciences

There are numerous models explaining the widely debated Laramide orogenic event that occurred in western North America from ~80-40 Ma. The shallowing of the subduction slab, or more likely a section of the slab, may have created the compressional regime that was expressed well inboard of the trench. Geologic evidence of this contraction has been documented from Canada down into Sonora, Mexico and includes the under-thrusting of the amphibolite facies Rand-Orocopia-Pelona schists, up­­lift of the continental interior and the “migration” of magmatism reaching ~1000 km inboard of the arc. Despite the abundant geologic data for Laramide and pre-Laramide orogenies, the initial magmatic units remain poorly understood. The characterization of these units may bring a better understanding of the transition to shallow slab subduction.
Using zircon U/Pb geochronology, a new suite of latest Cretaceous early Tertiary (i.e. 86-70 Ma) granitic intrusives has been characterized in the eastern-most Peninsular Ranges batholith. Previously, a small group of granitoids in the eastern Santa Rosa Mountains in southern California were the only characterized units of this age found in the Jurassic-Cretaceous Peninsular Ranges. This suite is sparsely exposed for at least 300 km along strike and likely comprises >200 km2 in surface outcrop exposure. The units lie within three geographically distinct areas. The youngest truly Laramide in age units (i.e. 80-70 Ma) were found in the Sierra Cucapas just south of the California-Baja California border whereas “transitional” aged units (i.e. 86-81 Ma) were identified in the Sierra Cucapa and further south in the Sierra San Felipe. Transitional aged units were also confirmed in the Santa Rosa Mountains of central southern California. Both the Laramide and transitional units in Mexico are found to be in cross-cutting relationship with the older La Posta-type plutonic rocks that comprise the main phase (100-90 Ma) of the eastern Peninsular Ranges batholith. The transitional units in the Santa Rosa Mountains appear to be distinctly to the east of La Posta aged units which are separated by the eastern Peninsular Ranges mylonite zone.
Major and minor elemental geochemistry from 54 samples indicate that although the majority of granitics in the eastern Peninsular Ranges are, as previously documented, part of the La Posta suite, many do not follow the typical documented deep crustal root signature defined by high Sr/Y ratios. The Laramide and transitional aged samples were found to overlap almost completely with the La Posta aged suite of this study on a regional and local scale, making characterization difficult.
The eastern batholith has been described as a “migrating” arc representing the initial stage of inboard migration of Laramide Cordilleran magmatism. The new data however, suggests that following the voluminous La Posta magmatic flare-up at 100-90 Ma, magmatism stalled but continued intermittently until ~70 Ma in the eastern Peninsular Ranges batholith. With numerous examples of Late Cretaceous magmatism as far inland as Colorado and New Mexico, it now appears that magmatism did not simply “migrate” inboard and that current models of shallow subduction inadequately account for the proximal Laramide intrusions of this study. This suite therefore provides a unique area that records the tectonics and magmatism associated with this major transition in Cordilleran geology.

New Publication - Lindsey Leighton & Stephen Schellenberg

Featured PALAIOS Article - January 2008

INFLUENCE OF SPATIOTEMPORAL SCALE ON THE INTERPRETATION OF PALEOCOMMUNITY STRUCTURE: LATERAL VARIATION IN THE IMPERIAL FORMATION OF CALIFORNIA

CORY M. REDMAN1, LINDSEY R. LEIGHTON*,2, STEPHEN A. SCHELLENBERG2, CHRISTOPHER N. GALE2, JENNIFER L. NIELSEN2, DONALD L. DRESSLER2 and MARY K. KLINGER2

1 Department of Biology, San Diego State University, San Diego, California 92182-4614, USA; Current address: Department of Geology and Geophysics, Texas A&M University, 3115 TAMU, College Station, Texas 77843-3115, USA
2 Department of Geological Science, Allison Center for Earth System History, San Diego State University, San Diego, California 92182-1020, USA

Numerous paleocommunity studies of marine ecosystems have demonstrated that water depth was the primary factor structuring paleocommunities. In contrast, many ecological studies find other factors play a greater role in delineating communities; this difference in results may be owing to the spatiotemporal scale at which the study is performed. To explore this hypothesis, the present study examines a set of Imperial Formation (Pliocene, California) paleocommunities at a scale potentially fine enough to exclude depth as a control over the communities, thus facilitating recognition of fine-scale ecological and environmental processes operating at this scale. Twenty-six taxa from 21 samples were collected in situ from an 8.5-m-thick interval within a 0.32 km2 area. Cluster, Bray-Curtis (polar) ordination, and detrended correspondence analyses were used to infer community structure. Cluster and ordination analyses produced similar results independent of choice of distance measure. To test whether depth would be the primary control, even at fine scales, the scores from the first ordination axis for each taxon were compared with their modern mean depth; no strong correlation exists between depth and ordination scores. Cluster and ordination results indicate that life mode (as determined by modern relatives) and to a lesser extent, grain size, were the primary factors influencing paleocommunity structure at this scale. Bivalve taxa were grouped by life mode: quasi-infaunal, shallow-burrowing infaunal, byssate, and cemented. Relative to paleoecological studies conducted on much broader spatiotemporal scales, this study highlights the potential utility of embedding fine-scale studies within broader-scale studies to capture and investigate additional sources of ecological and environmental variation.

Abstract . Full Text . PDF (1.31M)

PALAIOS; December 2007; v. 22; no. 6; p. 630-641; DOI: 10.2110/palo.2006.p06-044r

SEMINAR - Christian Koeberl

Meteorite impact cratering on Earth:
Geological and biological consequences

Dr. Christian Koeberl
Department of Geological Sciences
University of Vienna, Austria

Wednesday, December 5th, 1:00pm GMCS 422

Impact is a unique, short-time, high-energy geological process. The importance of impact cratering on terrestrial planets (Mercury, Venus, Mars), our Moon, and the satellites of the outer planets is obvious from the abundance of craters on their surfaces. On most bodies of the solar system that have a solid surface, impact cratering is the most important surface-modifying process even today. On Earth, active geological processes rapidly obliterate the cratering record. To date only about 170 impact structures have been recognized on the Earth’s surface. They come in various forms, shapes and sizes, from 300 km to less than 100 m in diameter, from Recent to 2 billion years in age. Mineralogical, petrographic, and geochemical criteria are used to identify the impact origin of such structures or related ejecta layers. The two most important criteria are the presence of shock metamorphic effects in mineral and rock inclusions in breccias and melt rocks, as well as the demonstration, by geochemical techniques, that these rocks contain a minor extraterrestrial component. In impact studies there is now a trend towards the use of interdisciplinary and multi-technique approaches to solve open questions. In this lecture we will take a look at impact craters on the Earth (and some other planets), and discuss how they formed and how they can be recognized. An aspect of impact cratering that may be underestimated is the influence of impacts on the geological and biological evolution of our own planet. Even the impact of relatively small asteroids or comets can have disastrous consequences for our civilization. There is a 1 in 10,000 chance that a large asteroid or comet 2 km in diameter (corresponding to a crater of about 25-50 km in diameter) may collide with the Earth during the next century, severely disrupting the ecosphere and annihilating a large percentage of the Earth's population. The biological evolution of our planets is punctuated by mass extinction events, of which the one 65 million years ago, which marks the Cretaceous-Tertiary boundary, is probably the best known one. Abundant impact debris marks this boundary, providing a clear link with a major impact event. The Chicxulub impact structure in Mexico, about 200 km in diameter, which resulted from the impact of an about 10-km-diameter asteroidal body, has been identified as the culprit. Understanding of impact structures, their formation processes, and their consequences should be of interest not only to earth and planetary scientists, but also to society in general.


Christian Koeberl is a professor at the Department of Geological Sciences at the University of Vienna, Austria, whose main research interest is the interdisciplinary study of meteorite impact craters, including shock petrography and the geochemistry of impactites, and also works on meteorites. He was the chairman of the European Science Foundation (ESF) “IMPACT” program (1998-2003), and is a member of the International Continental Scientific Drilling Program (ICDP) Science Advisory Group. He has published over 300 peer-reviewed research papers and has written or edited 12 books.

SEMINAR - Anne Sheehan

Seeing Beneath Mount Everest:
Probing a Breeding Ground of Destructive Earthquakes

IRIS/SSA Distinguished Lectureship
Dr. Anne Sheehan
University of Colorado, Boulder

Wednesday, November 28th, 1:00pm GMCS 422

The Himalaya mountains are the product of the largest continental collision in the world today, and are home to large and deadly earthquakes, such as the Pakistan earthquake of October 8, 2005. To understand how the mountains were created and to help quantify the earthquake hazards of this vulnerable region, Dr. Sheehan led a National Science Foundation funded project that included placement of ground motion recorders (seismometers) throughout eastern Nepal and southern Tibet. The seismic stations were installed in areas that are remote and logistically difficult, with challenges including the mountains, weather, scorpions, cobras, and political unrest and guerrilla warfare in Nepal. Much like a medical CT scan, ground motion recordings from earthquakes provide a detailed image of the Earth beneath the seismic stations. The earthquake recordings collected in Nepal and Tibet produce a first-ever glimpse of the earthquake faults beneath the Himalayan mountains, and can be used to determine details of the earthquake faulting processes.

About Dr. Sheehan
Education
Ph.D., Massachusetts Institute of Technology, 1991B.S., University of Kansas, 1984
Positions Held
Professor, University of Colorado, Boulder 2006-presentAssociate Professor, University of Colorado, Boulder 2001-2006Assistant Professor, University of Colorado, Boulder 1993- 2000Fellow, Cooperative Institute for Research in Environmental Sciences 1993-PresentResearch Assistant Professor, University of Nevada, Reno 1992-1993Postdoctoral Fellow, Lamont-Doherty Geological Observatory, Columbia University, 1991- 1992
Honors and Awards
NSF CAREER Award, 1995

Dr. Anne Sheehan joined the faculty at the University of Colorado at Boulder in 1993 and is currently a Professor of Geological Sciences and Fellow of the Cooperative Institute for Research in the Environmental Sciences. Sheehan's research interests include the study of crust and upper mantle structure of the Earth and its relation to tectonic deformation, particularly beneath mountains and plate boundaries. Much of her work includes the deployment of portable seismometers that record both distant and local earthquakes. She has led recent seismic experiments in the Himalaya, New Zealand, and the Rocky Mountains.

Sheehan is an experienced public speaker and has given talks about her research to many school and community groups. Sheehan was the 2005-2006 Science Advisor to CU Science Explorers. This program offers hands-on workshops throughout the state of Colorado on science topics to teams of middle school teachers and students. Sheehan worked with Science Explorers staff to develop a curriculum on Natural Hazards, including earthquakes and tsunamis, avalanches, and forest fires. Sheehan teaches introductory geology at the University of Colorado to a class of 180 students, and consistently receives high marks for her teaching. She also teaches advanced undergraduate level and graduate level courses in geophysics and seismology.
Sheehan is married and has two school-age children. She enjoys coaching youth sports and participating in triathlons and bicycling events. Sheehan is a breast cancer survivor and is active with Rocky Mountain Team Survivor.

Books
Burger, H. R., A. F. Sheehan, and C. H. Jones, Introduction to Applied Geophysics: Exploring the Shallow Subsurface, W. W. Norton Publishers, 2006.

Selected Recent Publications
Schulte-Pelkum, V., G. Monsalve, A. F. Sheehan, M. Pandey, S. Sapkota, R. Bilham, and F. Wu, Imaging the Indian subcontinent beneath the Himalaya, Nature, v. 435, pp. 1222-1225, 30 June 2005doi:10.1038/nature03678, 2005.De la Torre, T., and A. F. Sheehan, Broadband seismic noise analysis of Himalayan Nepal Tibet Seismic Experiment, Bull. Seismol. Soc. Am., v. 95, 1202-1208, doi:10.1785/0120040098, 2005.Sheehan, A. F., V. Schulte-Pelkum, O. Boyd, and C. Wilson, Passive source seismology of the Rocky Mountain region, in The Rocky Mountain Region: An Evolving Lithosphere, Geophysical Monograph Series 154, 10.1029/154GM23, p. 309-315, 2005.
Boyd, O. S., C. H. Jones, and A. F. Sheehan, Foundering lithosphere imaged beneath the Southern Sierra Nevada, California, Science, v. 305, 660-662, 2004.
Gilbert, H. J., and A. F. Sheehan, Images of crustal variations in the intermountain west, Journal of Geophysical Research, v. 109, B03306, doi:10:1029/2003JB002730, 2004.
Blume, F., and A. F. Sheehan, Quantifying seismic hazard in the Southern Rocky Mountains through GPS measurements of crustal deformation, in Engineering Geology in Colorado: Contributions, Trends, and Case Histories, eds. D. Boyer, P. Santi, and W. Rogers, Association of Engineering Geologists Special Publication No. 15, Colorado Geological Survey Special Publication 55, 2003.Lastowka, L. A., A. F. Sheehan, and J. M. Schneider, Seismic evidence for partial delamination model for Colorado Plateau uplift, Geophys. Res. Lett.,v. 28, 1319-1322, 2001.
Sheehan, A. F., Microearthquake study of the Colorado Front Range: Combining research and teaching in seismology, Seismol. Res. Lett., v. 71, 175-179, 2000.Savage, M. K., and A. F. Sheehan, Seismic anisotropy and mantle flow from the Great Basin to the Great Plains, western United States, Journal of Geophysical Research, v, 105, 13715-13734, 2000.Sheehan, A. F., P. M. Shearer, H. Gilbert, and K. G. Dueker, Seismic migration processing of P-SV converted phases for mantle discontinuity structure beneath the Snake River Plain, western United States, Journal of Geophysical Research, v. 105, p. 19055-19065, 2000.Shen, Y., A. Sheehan, K. Dueker, C. de Groot-Hedlin, and H. Gilbert, Mantle discontinuity structure beneath the southern East Pacific Rise (MELT experiment region) from P-to-S converted phases, Science, v. 280, 1232-1235, 1998.Dueker, K. G., and A. F. Sheehan, Mantle discontinuity structure from mid-point stacks of converted P to S waves across the Yellowstone hotspot track, Journal of Geophysical Research, v. 102, 8313-8327,1997.

2007 Science Sampler

Science Sampler

Sunday, November 18, 2007

A Science Experience on for San Diego Area High School Students Given by SDSU School of Sciences Departments

The Menu:
Oriented toward San Diego County High School Students. A series of short presentations, experiments and labs Hands on, interactive activities demonstrating scientific principles. A sampler of the best of selected science fields. Visitor participation includes a write-up and proof of attendance certificate.

Purpose for High School Students:
Expose High School students to neat science stuff. Experience science in action and take part in experimental science.

Purpose for High School Science Teachers who are welcome:
Support local High School Science Teachers: Provide a local field trip and meet Selected State of California Science Standards

Science Areas:
SDSU School of Sciences Departments Instructions: Students can come by themselves or with others. Suggested arrival at SDSU before 1 :30 PM. for pre-show tour. Go to Geology, Mathematics, Computer Science (GMCS) building Room 333 at SDSU

Campus Directions and Parking Information GMCS Map

November Crossword Puzzle - Seismology

Java Interactive Puzzle

Printable Puzzle (pdf)

SDSU Geology Faculty, Staff, and Alumni Help Support Injured Soldiers Program and San Diego Adaptive Sports Foundation

SDSU Geology Faculty, Staff, and Alumni David Huntley, Marie Grace, Diane Murbach, Monte Murbach, and Matt Weidlin Join the fifth annual Shelter Island 5K RUN/WALK to benefit the Injured Soldiers Program (Injured US Military)and the San Diego Adaptive Sports Foundation.

Dave Huntley came in FIRST in his age group and Diane Murbach came in THIRD in her age group for women.

Registration & Results

SEMINAR - Gareth Funning

Space geodesy in the San Francisco Bay Area: surface deformation, fault kinematics and creep

Gareth Funning
Department of Earth Science
Univeristy of California Riverside

Wednesday, November 14th, 1:00pm GMCS 422

Pacific-North America relative motion is accommodated north of San Francisco on a series of sub-parallel strike-slip faults. From GPS data, we understand the broad distribution of slip between these stuctures, but data are too sparse to map the deformation in detail. However, using an advanced form of InSAR processing - the Permanent Scatterer method - we can generate a dense spatial dataset of surface velocity measurements. There now exist three such datasets for the Bay Area, each from a different viewing geometry/satellite track.

We find a variety of nontectonic and tectonic signals in these data, ranging from ground subsidence and landsliding to strain accumulation and fault creep. I will prsent a series of case studies from around the Bay Area, showing how the different observation geometries can be used to make first order inferences of horizontal and vertical velocities in deforming areas, how the data were used to identify creep on a fault previously considered locked, and how using the pattern of creep on the Hayward fault - currently considered the most dangerous structure in the region - a series of locked asperities can be imaged geodetically.

Inner Space/Outer Space

Department Photo Gallery

SAGE Turns 25

A model of success
Summer of Applied Geophysical Experience program turns 25

It's as heavy as a cement truck, but it works like a watch," said 1 Lawrence "Larry" Braile, a professor from Purdue University. He was referring to the massive, roaring industry-grade piece of machinery called the Vibroseis truck shaking the ground on a mesa near Santo Domingo Pueblo roughly half way between Santa Fe and Albuquerque. Braile, other instructors, and twenty-four students participated in the Laboratory sponsored Summer of Applied Geophysical Experience (SAGE), which turned 25 this summer. The machine is what industry calls a truck-mounted vibrator. The Vibroseis truck, through a heavy pad on the ground, sends benign vibrational waves as deep as two to three kilometers into the ground that refract and reflect off layers of higher density, showing the students and the instructor where there is a change in the rock layers, for example. For the past 25 years SAGE has attracted the best students from around the world interested in geophysics. The application process isn't difficult; however, students must meet certain academic standards, such as successfully completed courses in physics and math. SAGE instructors are mostly looking for interest and motivation. A major in geophysics is not required. Members of the SAGE faculty are among the best in the nation. Additionally, SAGE attracts some the best companies in geophysics, geology, and geological/mineral exploration. Students at SAGE familiarize themselves with state-of-the-art equipment and the latest software, much of it donated by companies. Interest, motivation, and dedication drive SAGE. In the dry desert air with a storm looming to the west, a level of focus and eagerness to learn permeated through students and instructors alike. SAGE is outstanding and long lasting because of its instructors, the core six who have been with SAGE most of the 25 years. The core faculty consists of

• Scott Baldridge of Geophysics (EES-1 I), co-director
• George Jiracek, co-director and professor of geology from San Diego State University
• Lawrence (Larry) Braile, professor and department head of earth and atmospheric sciences, Purdue University
• Shawn Biehler, professor of earth sciences at University of California, Riverside
• Bernard (Bernie) Gilpin, professor of physics and geology at Golden West College
• John Ferguson, associate professor and program head of the geosciences department at the University of Texas.

According to Baldridge, the faculty is "like a good baseball team. They work together well, and there is a high level of individual commitment." Besides the core faculty, several newer staff members from Los Alamos, the U.S. Geological Survey, and Green Engineering consulting firm have joined the program to advance the students' experience. In addition, geophysicists from several companies lead field experiments and assist with instructing students. Since the beginning of the program, a huge focus has been on what could be improved for the next session. How could the students get a more satisfying experience from SAGE?

The faculty has made SAGE a flexible and adaptable program. SAGE,like any long-surviving program, has undergone changes that have been"more evolutionary than revolutionary," said Baldridge.An example of such a change is the size and length of the program.The first SAGE program in 1983 had 42 students and lasted six weeks. Incontrast, the 25 SAGE program had 24 students and lasted three weeks,allowing each student to have hands on experience and individualattention without completely exhausting the instructors.The original SAGE was intended for students of participating facultyonly. Now, student diversity is a main goal and is oft cited as one ofthe most valuable characteristics of the program. Though some of theforeign nationals in SAGE currently are studying in the United States,students from Mexico, Saudi Arabia, Lebanon, Germany, Sweden, andIndia have participated in SAGE.The structure of SAGE also has undergone change to ensure each studentgets the full experience. Instead of having one big group of studentsworking sequentially from project to project, students are split up intoteams and spread out around the area where SAGE is working at the time.In addition to the major support of the Department of Energy and theNational Science Foundation, a significant portion of SAGE is funded byindustry involvement. Companies support SAGE with funding, personneland the latest software and equipment. The Vibroesis truck was donatedto SAGE by the executive vice president of Input/Output, a former SAGEstudent himself.Companies are in turn invited to send representatives to SAGE to talkto, work with, and help teach students. Representatives promote jobopportunities in the field and bring a sense of reality to the work."We're really interested in this experience," said Betsy Torrez, geosciencerecruiting coordinator from ConocoPhillips. "We want to help outand enhance the program here, as well as offer career opportunities."After 25 years, SAGE is running like clockwork. It's had its own "downyears," said Baldridge, but it survived with support from the industriesinvested in SAGE. And like a fine wine, SAGE is only improving thanks tothe faculty's dedication to providing the students' with a quality experience,and the general willingness to be flexible.

by Caryn Johansen
LOS Alamos Newsletter, Week of October 22, 2007

SEMINAR - Jasper Konter

The Origin and Geologic Evolution of Seamounts in the Pacific Ocean

Jasper Konter
Department of Geological Sciences
San Diego State University

Wednesday, November 7th, 1:00pm GMCS 422

The “hotspot” hypothesis predicts that time-progressive linear chains of oceanic intraplate volcanoes (OIV) are formed on tectonic plates that pass over buoyantly rising plumes from fixed deep mantle sources. However, this hypothesis has been called into question by an alternate mechanism, which explains OIV chains by lithospheric extension and mantle melts rising to the surface along lithospheric fractures. Distinguishing between these models is very important because they imply a profoundly different dynamic and chemical state of the mantle that is likely to substantially influence the chemical evolution of the Earth. I will present new geochemical data from a geochemical study of several seamount chains in the Western Pacific, all likely erupted over the seismically anomalous Pacific mantle. These data provide a >100 myr geochemical record that can be related to three geochemically distinct active OIVs in the Cook-Austral region with the help of plate motion models. In a geophysical and geodynamic context these volcanoes should most likely be viewed as the result of deep mantle plumes, while lithospheric cracks are probably a secondary factor.

SEMINAR - Nadia Lapusta

Insights from modeling long-term slip histories of faults governed by
laboratory-derived friction laws

Nadia Lapusta
Mechanical Engineering and Geophysics
California Institute of Technology

Wednesday, October 31st, 1:00pm GMCS 422

We have been developing methodology that allows us to simulate long histories of seismic and aseismic fault slip while accounting for slow tectonic loading and all inertial effects. Our 3D models incorporate laboratory-derived rate and state friction laws. We have used 3D models to simulate interaction of seismic and aseismic slip, to reproduce abnormal scaling of moment and recurrence time for small repeating earthquakes, and to study interaction of dynamic rupture with fault heterogeneities over many earthquake cycles. In 2D models, additional dynamic weakening mechanisms due to shear heating are incorporated, When combined with defect regions to nucleate ruptures, fault models with high static friction strength and low dynamic strength operate under low average shear stress and low heat production, while producing earthquakes that have typical stress drops and pulse-like mode of rupture propagation. Hence the models reconcile several laboratory and observational constraints. Decrease in dynamic weakening causes the fault to operate at higher average levels of shear stress and results in systematic change of rupture mode from pulse-like to crack-like. Such change of dynamic rupture mode with fault prestress has been recently documented in laboratory experiments.

San Diego Fire Watch - Google Earth

MODIS Active Fire Mapping Program

WMS and KML Access
The data links below provide access to MODIS MOD14 fire and thermal anomaly data in both a Web Mapping Service (WMS) and Keyhole Markup Language (KML) format for each specified geographic area. Both the WMSes and KMLs are updated hourly.

GOOGLE EARTH (KMZ): Download
2007 WMS: Information
2001-2006 WMS: Information

These fire information products were compiled at the USDA Forest Service (USFS) Remote Sensing Applications Center in cooperation with NASA Goddard Space Flight Center, the University of Maryland, the National Interagency Fire Center, and the USFS Missoula Fire Sciences Lab.

GOES Western US SECTOR Visible Image
October 21st - 24th

New Publication - Pat Abbott

Natural Disasters, 6th Edition

Patrick Leon Abbott
©2008, ISBN-13 9780073292328
MHID 007329232X

Description
This book focuses on natural disasters: how the normal processes of the Earth concentrate their energies and deal heavy blows to humans and their structures. It is concerned with how the natural world operates and, in so doing, kills and maims humans and destroys their works. Throughout the book, certain themes are maintained: * energy sources underlying disasters * plate tectonics and climate change * earth processes operating in rock, water, and atmosphere * significance of geologic time * complexities of multiple variables operating simultaneously * detailed and readable case studies.

Table of Contents
1 Natural Disasters and The Human Population
2 Energy Flows in Earth History and Natural Disasters
3 Plate Tectonics and Earthquakes
4 Earthquake Geology and Seismology
5 Tsunami
6 Earthquakes in Western North America
7 More U.S. and Canadian Earthquakes
8 Volcanic Eruptions: Plate Tectonics and Magmas
9 Volcano Case Histories: Killer Events
10 Mass Movements
11 Atmosphere, Oceans, and Long-Term Climate Change
12 Short-Term Climate Change and Severe Weather
13 Hurricanes and the Coastline
14 Floods
15 Fire
16 The Great Dyings
17 Impacts with Space Objects

About the Author
Pat Abbott is a professor at San Diego State University

Features

• New feature: Entire text has been revised to feature 4-color line drawings and photos.
  Case Histories: The text aims to explain important principles about the Earth and then develop further understanding through numerous case studies.


• End-of-Chapter Learning Aids: Learning aids at the conclusion of every chapter include Terms to Remember, Questions for Review and Questions for Further Thought.


• Organization: The primary organization of the book is based on an energy theme. Chapter 1 leads off with data describing natural disasters and the human population. Chapter 2 examines the energy sources underlying disasters. Disasters fueled by Earth’s internal energy are addressed in Chapters 3 through 9 and are organized on a plate-tectonics theme, with the new Chapter 5 discussing tsunami. Disasters powered primarily by gravity are covered in Chapter 10 on mass movements. Disasters fueled by the external energy of the Sun are examined in chapters 11 through 15. Chapter 16 examines the great dyings encased in the fossil record. Chapter 17 examines impact mechanisms in greater detail and includes plans to protect Earth from future impacts.


• Comprehensiveness: The text covers the most significant natural hazards, from geologic to oceanographic to atmospheric to astronomic to demographic, and their associated phenomena. The broad range of natural disasters topics allows each instructor to select those chapters that cover their interests and local hazards.
  New chapter exclusively covering tsunami.

SEMINAR - Jared Morrow and Bennett Spevack

3-D seismic, well log, and petrographic analyses of the Victoria Island structure, a potential buried impact crater, San Joaquin county, California

Jared Morrow
Department of Geological Sciences

San Diego State University

Bennett Spevack

ABA Energy Corporation

Bakersfield

Wednesday, October 17th CSL 422, 1pm

Introduction:

Analyses of a 3-D seismic survey and well logs in the southwestern Sacramento basin, San Joaquin County, California, have revealed a subsurface, circular, ~5.5-km-diameter anomaly that may represent a previously unrecognized complex impact crater (Figs. 1–3). This unique anomaly, buried 1,490– 1,600 m below sea level under the southwestern part of the Sacramento-San Joaquin Delta, is provisionally named the Victoria Island structure for an overlying surface geographic feature.

Description:

The Victoria Island structure is characterized by a concentric, annular, terraced rim and trough surrounding a structurally uplifted central peak (Figs. 3–4). Well logs tied to seismic data show that the upper surface of the structure occurs stratigraphically near the top of the siliciclastic, continental to shallow-marine Domengine Formation, indicating a middle Eocene age [1]. Overlying fill material, which reaches an estimated thickness of at least 80 m in the trough, is primarily deep-marine, middle Eocene Nortonville Shale. Both well and seismic data indicate thinned Domengine and thickened Nortonville sections across the center of the feature (Figs. 1–3). A disturbed stratigraphic sequence under the structure includes upper to lower Domengine and underlying lower Eocene Capay Formation and Cretaceous- Paleocene Mokelumne River Formation siliciclastic units. Characterized by discontinuous seismic reflectors (Fig. 3), the central peak is estimated to be ~600 m in diameter with at least 35 m of structural uplift. The seismic data demonstrate that the feature is ‘rootless’, being underlain by gently dipping, relatively undeformed strata (Fig. 3). The 3-D data further suggest the presence of a series of discontinuous, inwarddipping, concentric normal faults with minor offset surrounding the trough and outer rim areas. Estimates of the dimensions of the structure indicate a circularity ratio (short-to-long axes) of 0.91 and a depth-todiameter ratio of ~0.02.

Ongoing Work:

The observations above, including the seismic expression, complex morphology with central uplift, high circularity, depth-to-diameter ratio, and anomalous setting of the structure, are most consistent with documented, diagnostic characteristics of impact craters [2–4]. Ongoing petrographic work is examining drill cuttings from wells within and around the structure, to seek such additional impact indicators as an impactite layer, shocked mineral grains, glass fragments, or melt particles, and to assess the feasibility of future geochemical analyses of the structure. Supplemental cuttings and well log data may also further constrain the stratigraphic age of the structure within the Domengine-Nortonville interval. Together with the previously proposed, 1.3-km-diameter, Miocene- age Cowell structure [5], the Victoria Island structure represents the second potential buried impact crater from California’s Central Valley region.

Acknowledgments:

John Spray, Richard Pike, and Raymond Sullivan gave helpful input during the early phases of the project. ABA Energy, Bakersfield, CA, and Rising Star Energy, L.L.C., Dallas, TX, are gratefully acknowledged for providing access to seismic data, well logs, and well cuttings used in the project. The California Well Sample Repository, Bakersfield, CA, is also thanked for providing additional well log data and cuttings currently under study.

References:

[1] Sullivan M. D. et al. (2003) Pac. Sec. SEPM Guidebook 94, 51 p. [2] Melosh H. J. (1989) Impact cratering, a geological process, Oxford Univ. Press, 245 p. [3] Therriault A. M. et al. (2002) Bull. Czech Geol. Survey 77(4), 253–263. [4] Stewart S. A. (2003) Geology 31(11), 929–932. [5] Blake R. G. (1998) AAPG Bull. 82(5A), 842.

Figure 1. Isopach map of potential crater infill, between
upper Nortonville Shale marker (blue line, Fig. 3) and base
Nortonville Shale/top Domengine Formation marker (red
line, Fig. 3). Colored isopach scale is in meters. West-toeast
seismic profile line A–A’ (Fig. 3) is indicated; other
letters correspond to well locations.

Figure 2. Isopach map of interval between
upper Nortonville Shale marker (blue line, Fig.
3) and lower Domengine Formation marker
(green line, Fig. 3), showing series of concentric
circular ridges and troughs, together with positions
of several major, curvilinear normal faults
that surround the structure and cut the lower
part of the isopached interval. Colored isopach
scale is in meters. West-to-east seismic profile
line A–A’ (Fig. 3) is indicated; other letters
correspond to well locations.

Figure 3. West-east seismic profile across
structure (A–A’, Figs. 1– 2). Stratigraphic markers:
Blue– upper Nortonville Shale; red– base
of Nortonville Shale/top of Domengine Formation;
green– lower Domengine Formation; yellow–
approximate base of Capay Formation/top of
Mokelumne River Formation. Selected major,
concentric normal faults (Fig. 2) that intersect the
profile are shown schematically by black lines.

Figure 4. Oblique, inverted 3-D-view isopach
map of potential crater infill. Map is based on
same isopach interval as in Figure 1, between
upper Nortonville Shale and base Nortonville
Shale/top Domengine Formation markers. Vertical
exaggeration is 20X. Isopach colors and thicknesses
are the same as in Figure 1. Note north arrow.

Source:
Lunar and Planetary Science XXXVIII (2007)
3-D SEISMIC AND WELL LOG ANALYSES OF THE VICTORIA ISLAND STRUCTURE, A POTENTIAL BURIED IMPACT CRATER, SAN JOAQUIN COUNTY, CALIFORNIA.
S. C. Spevack1, J. R. Morrow2, and B. Z. Spevack3,
1Grossmont Middle College High School, El Cajon, CA 92020,
2Department of Geological Sciences, San Diego State University, San Diego, CA 92182-1020 (jmorrow@geology.sdsu.edu),
3ABA Energy Corporation, Bakersfield, CA 93308.

October Crossword Puzzle - Mineralogy

Java Interactive Puzzle

Printable Puzzle (pdf)

SEMINAR - Dave Kimbrough

Growth and recycling of continental crust—new insight from the Peninsular Ranges batholith of southern and Baja California
Dr. Dave Kimbrough
Department of Geological Sciences
San Diego State University
Wednesday, October 10th CSL 422, 1pm

Mesozoic-Cenozoic circum-Pacific batholiths are a prime example of convergent continental margin magmatic processes thought to drive growth and maturation of continental crust. Although it's now clear that non-steady-state magmatic flare-ups of ~5-15 Ma duration account for the bulk of magmatic addition in long-lived continental margin arcs, understanding of deep crust & mantle processes related to the build-up and triggering of flare-up events remains elusive. “La Posta-type” intrusions that dominate the eastern Peninsular Ranges batholith of southern and Baja California provide an important perspective on this issue. These rocks are chemically similar to high-Al tonalite-trondhjemite-granodiorite gneiss terrains of Archean crust produced by high pressure melting of mafic source regions. New zircon U-Pb ages (n=43) from most of the major La Posta intrusive centers document synchronous and surprisingly brief emplacement at 96±3 Ma throughout this 1600-km long batholith segment. High del18O values of La Posta-type zircon (~7-11 per mil) indicate large components of supracrustal contaminants into deep crustal magma source regions. Because the volume La Posta-type crust in the Peninsular Ranges may easily exceed a million cubic kilometers, simple mass balance considerations require supracrustal recycling on a massive scale. The fact that high del18O La Posta-type zircon are from rocks with Sri values mostly <0.706 constrains the nature of the supracrustal contaminant. Assimilation of high Sri Julian Schist-type metasedimentary wallrock to account for La Posta zircon oxygen isotope compositions is unrealistic on several counts. We speculate that large-scale sediment underplating of isotopically primitive accretionary prism material may have played an important role leading up to La Posta-type melt generation. This view is supported by a sediment deficit in adjacent forearc basin & accretionary prism belts of the California borderland.

SEMINAR - Gary Peterson

The Cryogenic World of Triton
Dr. Gary Peterson
Department of Geological Sciences
San Diego State University
Wednesday, October 3rd CSL 422, 1pm

Triton is a large satellite in retrograde orbit around Neptune, the most distant (40AU) of the giant gaseous planets. Surface temperatures average about 40K and are cold enough to condense all of the heavier gases, including nitrogen. A pronounced tilting of Triton's spin axis gives rise to a strongly seasonal climate and the available imagery indicates a deteriorating south polar cap made of nitrogen. Evidently the released nitrogen is being transferred to the north pole and condensing there during the long winter season. Distant though the sun is, it evidently supplies enough energy to provide seasonal transfer of nitrogen much in the same manner that water alternately collects and melts at the earth's poles with the seasons. Triton has been resurfaced and shows little evidence of cratering. Probably the satellite has been heated, evaporating the surface ices and then the released gases have recondensed to provide a new surface. The energy source for the heating would appear to be tidal friction following capture by Neptune. The retrograde orbit of Triton would indicate capture and the lack of surface craters would suggest that the capture was a fairly recent event. Numerous irregular surface textures indicate repeated expansion and contraction and are compared with somewhat similar features on earth. Although the Earth/Triton surface features resemble one another, they would be composed of totally different material.

The Independent Planetologist - Lecture Service

The United States and Russia have long-term Solar System exploration programs. These undertakings have provided us with detailed imaging at a variety of scales of all planets and major satellites except Pluto/Charon. Many more NASA projects are currently underway. Landings on Venus (Russia), Mars (U. S.) and the Moon (Russia and U. S.) greatly enriched the available imagery with rock samples and/or analyses.

How is this voluminous information to be interpreted? The only way to comprehend most of it is to place it within the context of our understanding of the Earth. That field of endeavor is Planetary Geology. The persons most adept at interpreting features of other planets and satellites would be those who are most adept at interpreting similar features on the Earth.

Gary enjoys public speaking and consider it a service to the university and community. Planetary Geology has become a passion and he enjoys sharing that passion. Gary likes meeting people with similar interests and exchanging observations and ideas. Offering public lectures is an excellent way of accomplishing those goals.

Go to the Indepentent Planetologist Web Site for more information....

New Publication - Jared Morrow

Physical and chemical evidence of the 1850 Ma Sudbury impact event in the Baraga Group, Michigan

Peir K. Pufahl*,1, Eric E. Hiatt2, Clifford R. Stanley3, Jared R. Morrow4, Gabriel J. Nelson5 and Cole T. Edwards6

1 Department of Earth and Environmental Science, Acadia University, Wolfville, Nova Scotia B4P 2R6, Canada
2 Department of Geology, University of Wisconsin, Oshkosh, Wisconsin 54901, USA
3 Department of Earth and Environmental Science, Acadia University, Wolfville, Nova Scotia B4P 2R6, Canada
4 Department of Geological Sciences, San Diego State University, San Diego, California 92182-1020, USA
5 Department of Earth and Environmental Science, Acadia University, Wolfville, Nova Scotia B4P 2R6, Canada
6 Department of Geology, University of Wisconsin, Oshkosh, Wisconsin 54901, USA

ABSTRACT

An ejecta layer produced by the Sudbury impact event ca. 1850 Ma occurs within the Baraga Group of northern Michigan and provides an excellent record of impact-related depositional processes. This newly discovered, 2–4-m-thick horizon accumulated in a peritidal environment during a minor sea-level lowstand that punctuated a period of marine transgression. Common ejecta clasts include shock-metamorphosed quartz grains, splash-form melt spherules and tektites, accretionary lapilli, and glassy shards, suggesting sedimentation near the terminus of the continuous ejecta blanket. Sedimentologic and geochemical data indicate that primary fallout from a turbulent ejecta cloud was reworked to varying degrees by an impact-generated tsunami wave train. Observed platinum group element anomalies (Ir, Rh, and Ru) within the Sudbury ejecta horizon are sufficient to suggest that the impactor was a meteorite. Documenting and interpreting the detailed characteristics of the Sudbury ejecta horizon in Michigan have yielded a fingerprint to identify this chronostratigraphic marker in other Paleoproterozoic basins. For the first time a foundation exists to assess the consequences of the Sudbury impact on Precambrian ocean chemistry and early life.

Geology; September 2007; v. 35; no. 9; p. 827-830; DOI: 10.1130/G23751A.1

SEMINAR - Avinoam Rabinovitch

Abstract

We have thoroughly studied the properties of electromagnetic radiation (EMR) emitted from fracturing materials. A model was suggested to explain these phenomena, which helped us relate EMR measured parameters with crack sizes and velocities.

Since EMR appears when fracturing only starts it might be useful as a tool to predict earthquakes in their latent period.

Avinoam's seminar title:
"Properties of electromagnetic radiation from fractures and the possibility of its use for earthquake forecast";
Wednesday the 19th of September 2007


Author of the
Tensile Fracturing in Rocks: Tectonofractographic and Electromagnetic Radiation Methods
Dov Bahat, Avinoam Rabinovitch, Vladimir Frid
Understanding tensile fracture in rocks provides an important key for the interpretation of many problems in structural geology. This book presents a multidisciplinary approach to tensile fracture in rocks (faulting is briefly addressed), starting with an introduction to fracture physics and progressing through tectonofractographic features, characterized both in experimental settings and in geological outcrops. Four examples of sedimentary rocks and two of granites have been chosen to demonstrate the principles and problems in fracture geology. Principles of fracture mechanics and rock mechanics are applied throughout the book, which also explores current understanding about electromagnetic radiation induced by fractures and how such radiation can be used to monitor and predict earthquakes and hazardous collapses in mines. The monograph serves not only as a manual on how to handle specific problems and their solutions in fractual geology but also as a starting point for researchers and graduate students interested in the field of rock fracturing.

Geol306 Structural Geology - La Jolla Fieldtrip Photos

Department Photo Gallery

The Big One - Earthquake risk in Southern California

The southernmost stretch of the San Andreas Fault is more than 150 years overdue for a large quake.

The San Andreas Fault stretches 800 miles from the Salton Sea at the southern end of California to the ocean just off Eureka in the north.
Skirting the foggy Bay Area, the fruitful heartland, and the bustling urban center of Los Angeles, it waits quietly.
For The Big One. An earthquake of 7.5 magnitude or greater that is certainly coming.

Experts say the normal probability for a large earthquake on any significant portion of the fault is once every 150 years; yet the southern portion has not “snapped” since 1690.
“We believe it’s accumulated more strain than other parts, like in San Francisco, where it broke with a large earthquake in 1906,” said San Diego State University seismologist Kim Bak Olsen.
The peacefulness, marked by smaller infrequent quakes, worries Olsen and his colleagues.
With extreme natural disasters – Hurricane Katrina, the Indonesian tsunami, the recent Peruvian earthquake – this calm before the storm can give rise to a lack of preparedness. The result is injury and death on a large scale when catastrophe strikes.

The prediction of natural disasters is still far from an exact science. However, Olsen and fellow SDSU seismologist Steven Day are working to learn more about the major scenarios the San Andreas is likely to produce, so Californians can prepare even if there is no answer to the question of when.
Their work may mean never having to say, “if only we had known,” when it comes to the powerful jolt the long-expected Southern California earthquake will deliver.

“Simulation helps us characterize the biggest events, which are also the rarest, the ones that really put a stress on society,” said Day. “We are trying to reduce that level of surprise.”
‘A gift’
Using extensive data on the geography of areas off of the fault, Olsen and Day have been working with the San Diego Supercomputer Center to create finely detailed video simulations of the fault’s most probable seismic activity and how these ruptures would unfold.
Olsen was the first person to do three-dimensional simulations of these kind 12 years ago while working toward a doctorate in geophysics at the University of Utah.

“It’s a relatively new thing to use supercomputers for these kinds of simulations, because they haven’t been around for that long,” Olsen said. “It’s like a gift for us seismologists; it’s a really big computational problem that hasn’t been possible to solve until now.”
Their latest round of simulations, dubbed TeraShake for the power of calculations, are so vividly detailed they reveal the direction, magnitude and duration of the shaking -- and some bad news for Los Angeles.
If the southern portion of the fault unzips from south to north, the very factors that have historically made L.A. such a desirable place to settle — majestic mountains and flat valleys, would cause it to shake violently for more than two minutes.
The energy from the quake would radiate outward from the likely epicenter near the Salton Sea, but not in stacked, even circles, as earthquakes are graphically conveyed on the evening news. Channeled toward L.A. by the San Gabriel Mountains, the waves would become trapped by the sedimentary basins situated underneath the city.
“The waves would bounce back and forth inside the basin, kind of like waves in a bathtub,” Olsen said. “This specific earthquake seems to be one of the worst-case scenarios.”

Other scenarios simulated in TeraShake include a north-to-south quake, in which Mexicali would experience the strongest shaking.
The trade-off
The information provided by TeraShake is potentially useful to engineers and policymakers in making decisions about new development in Southern California.
“Cities can take the information and basically not build hospitals and universities on those areas,” Olsen said.
If only it were that simple.

Because there is still no way to accurately predict the timing of natural disasters, politicians often find themselves torn between spending funds on catastrophic event preparation or on more clearly defined near-term needs.
According to Day, the results of this trade-off are particularly evident in Third World countries, where catastrophes of enormous magnitude are common. Funding preparedness means diverting money from urgent development projects.
“Our work doesn’t solve the political and economic problems entirely; it provides a scientific foundation for that,” Day said. “Ultimately, it depends on society’s willingness to pay the price for preparedness.”
Until major preparation measures don’t compete financially with other pressing public needs, Olsen and Day are doing what they can to define earthquake risks and raise public awareness for decision-makers and concerned citizens alike.
Even without sweeping changes to building codes and city planning, individuals can still take small – and potentially life-saving – measures to prepare for a major earthquake.
“If the public is aware of fault lines and their proximity to home or the workplace, they may be more likely to respond to the shaking of a large earthquake,” Olsen said. “Letting the public know they should secure bookshelves to the wall, and seek shelter under a solid table could save many lives during a significant shake.”
Olsen has even found a way to entertain as he educates. He contributed to the animated earthquake sequences for the IMAX Film “Forces of Nature” and the National Geographic film “Anatomy of an Earthquake.”
Related information

TeraShake
The San Andreas Fault
Southern California Earthquake Center
“Forces of Nature” IMAX film

Credits
Story by Lauren Coartney
Graphics by John Signer
Photographs by Tom Farrington, Instructional Technology Services
Banner photograph courtesy of FEMA News Photo
Edited by Coleen L. Geraghty

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