Tom Parsons
I conduct research aimed at improving our ability to forecast hazardous events like earthquakes and tsunamis. Specifically, I study how earthquakes trigger others, how crustal movements cause earthquake stresses, and how to convert geologic observations of earthquake and tsunami processes into quantitative forecasts of use to planners, insurers, and builders.
Professional Experience
1994-Present: Research Geophysicist, U. S. Geological Survey, Menlo Park, CA
1992-1994: National Research Council Postdoctoral Fellow
Education and Certifications
1992 – Ph.D. in Geophysics, Stanford University
1990 – M.S. in Geophysics, Stanford University
1988 – B.S. in Applied Geophysics, UCLA
Affiliations and Memberships*
Editor, AGU Advances, 2019-present
Editor in Chief, Journal of Geophysical Research, Solid Earth, 2009-2015
Editor in Chief, Tectonophysics, 2007-2009
Editorial Board, Tectonophysics, 2005-2007
Editorial Board, Geology, 1995-2000, 2005-2008
Member: Executive Committee, Working Group on California Earthquake Probabilities 2005-present
Member: SCEC Planning Committee, 2007-2009
Honors and Awards
Senior Scientist (ST): 1/15
Fellow American Geophysical Union, Elected 1/12
Fulbright Mutual Educational Exchange Grant USA-Greece: 2007-2008
Alumni Pillar of Achievement: Golden West College Outstanding Alumni Award (10/07)
Fellow Geological Society of America, Elected 10/97
Shoemaker Communication Award (10/00)
National Association of Government Communicators Gold Screen Award (12/00)
National Research Council Post-Doctoral Fellow (8/92)
Science and Products
Seismic evidence for widespread serpentinized forearc upper mantle along the Cascadia margin
Structure and mechanics of the Hayward-Rodgers Creek Fault step-over, San Francisco Bay, California
Post-1906 stress recovery of the San Andreas fault system calculated from three-dimensional finite element analysis
Crustal structure of the coastal and marine San Francisco Bay region, California
Global Omori law decay of triggered earthquakes: Large aftershocks outside the classical aftershock zone
Nearly frictionless faulting by unclamping in long-term interaction models
Very different crustal response to extreme extension in the southern Basin and Range and Colorado Plateau transition
A simple algorithm for sequentially incorporating gravity observations in seismic traveltime tomography
Static-stress impact of the 1992 Landers earthquake sequence on nucleation and slip at the site of the 1999 M=7.1 Hector Mine earthquake, southern California
Three-dimensional seismic velocity structure of the San Francisco Bay area
Heightened odds of large earthquakes near Istanbul: an interaction-based probability calculation
Wide-angle seismic recordings from the 1998 Seismic Hazards Investigation of Puget Sound (SHIPS), western Washington and British Columbia
Non-USGS Publications**
**Disclaimer: The views expressed in Non-USGS publications are those of the author and do not represent the views of the USGS, Department of the Interior, or the U.S. Government.
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Filter Total Items: 116
Seismic evidence for widespread serpentinized forearc upper mantle along the Cascadia margin
Petrologic models suggest that dehydration and metamorphism of subducting slabs release water that serpentinizes the overlying forearc mantle. To test these models, we use the results of controlled-source seismic surveys and earthquake tomography to map the upper mantle along the Cascadia margin forearc. We find anomalously low upper-mantle velocities and/or weak wide-angle reflections from the toAuthorsT. M. Brocher, T. Parsons, A.M. Trehu, C.M. Snelson, M. A. FisherStructure and mechanics of the Hayward-Rodgers Creek Fault step-over, San Francisco Bay, California
A dilatational step-over between the right-lateral Hayward and Rodgers Creek faults lies beneath San Pablo Bay in the San Francisco Bay area. A key seismic hazard issue is whether an earthquake on one of the faults could rupture through the step-over, enhancing its maximum possible magnitude. If ruptures are terminated at the step-over, then another important issue is how strain transfers throughAuthorsT. Parsons, R. Sliter, E.L. Geist, R.C. Jachens, B. E. Jaffe, A. Foxgrover, P. E. Hart, J. McCarthyPost-1906 stress recovery of the San Andreas fault system calculated from three-dimensional finite element analysis
The M = 7.8 1906 San Francisco earthquake cast a stress shadow across the San Andreas fault system, inhibiting other large earthquakes for at least 75 years. The duration of the stress shadow is a key question in San Francisco Bay area seismic hazard assessment. This study presents a three-dimensional (3-D) finite element simulation of post-1906 stress recovery. The model reproduces observed geoloAuthorsTom ParsonsCrustal structure of the coastal and marine San Francisco Bay region, California
As of the time of this writing, the San Francisco Bay region is home to about 6.8 million people, ranking fifth among population centers in the United States. Most of these people live on the coastal lands along San Francisco Bay, the Sacramento River delta, and the Pacific coast. The region straddles the tectonic boundary between the Pacific and North American Plates and is crossed by several strGlobal Omori law decay of triggered earthquakes: Large aftershocks outside the classical aftershock zone
[1] Triggered earthquakes can be large, damaging, and lethal as evidenced by the1999 shocks in Turkey and the 2001 earthquakes in El Salvador. In this study, earthquakes with Ms ≥ 7.0 from the Harvard centroid moment tensor (CMT) catalog are modeled as dislocations to calculate shear stress changes on subsequent earthquake rupture planes near enough to be affected. About 61% of earthquakes that ocAuthorsTom ParsonsNearly frictionless faulting by unclamping in long-term interaction models
In defiance of direct rock-friction observations, some transform faults appear to slide with little resistance. In this paper finite element models are used to show how strain energy is minimized by interacting faults that can cause long-term reduction in fault-normal stresses (unclamping). A model fault contained within a sheared elastic medium concentrates stress at its end points with increasinAuthorsT. ParsonsVery different crustal response to extreme extension in the southern Basin and Range and Colorado Plateau transition
Clustered about the southwest edge of the Colorado Plateau lie many highly extended terranes. Among these are metamorphic core complexes, distinguished by low-angle normal faults with sufficient offset to expose middle crustal rocks at higher elevation relative to the surrounding areas. About 150 km to the southwest, strong extension in the Salton Trough manifests itself very differently; high-angAuthorsTom Parsons, Jill McCarthy, George A. ThompsonA simple algorithm for sequentially incorporating gravity observations in seismic traveltime tomography
The geologic structure of the Earth's upper crust can be revealed by modeling variation in seismic arrival times and in potential field measurements. We demonstrate a simple method for sequentially satisfying seismic traveltime and observed gravity residuals in an iterative 3-D inversion. The algorithm is portable to any seismic analysis method that uses a gridded representation of velocity structAuthorsT. Parsons, R. J. Blakely, T. M. BrocherStatic-stress impact of the 1992 Landers earthquake sequence on nucleation and slip at the site of the 1999 M=7.1 Hector Mine earthquake, southern California
The proximity in time (∼7 years) and space (∼20 km) between the 1992 M=7.3 Landers earthquake and the 1999 M=7.1 Hector Mine event suggests a possible link between the quakes. We thus calculated the static stress changes following the 1992 Joshua Tree/Landers/Big Bear earthquake sequence on the 1999 M=7.1 Hector Mine rupture plane in southern California. Resolving the stress tensor into rake-paralAuthorsTom Parsons, Douglas S. DregerThree-dimensional seismic velocity structure of the San Francisco Bay area
Seismic travel times from the northern California earthquake catalogue and from the 1991 Bay Area Seismic Imaging Experiment (BASIX) refraction survey were used to obtain a three-dimensional model of the seismic velocity structure of the San Francisco Bay area. Nonlinear tomography was used to simultaneously invert for both velocity and hypocenters. The new hypocenter inversion algorithm uses finiAuthorsJ.A. Hole, T. M. Brocher, S.L. Klemperer, T. Parsons, H. M. Benz, K.P. FurlongHeightened odds of large earthquakes near Istanbul: an interaction-based probability calculation
We calculate the probability of strong shaking in Istanbul, an urban center of 10 million people, from the description of earthquakes on the North Anatolian fault system in the Marmara Sea during the past 500 years and test the resulting catalog against the frequency of damage in Istanbul during the preceding millennium, departing from current practice, we include the time-dependent effect of streAuthorsT. Parsons, S. Toda, R. S. Stein, A. Barka, J.H. DieterichWide-angle seismic recordings from the 1998 Seismic Hazards Investigation of Puget Sound (SHIPS), western Washington and British Columbia
This report describes the acquisition and processing of deep-crustal wide-angle seismic reflection and refraction data obtained in the vicinity of Puget Lowland, the Strait of Juan de Fuca, and Georgia Strait, western Washington and southwestern British Columbia, in March 1998 during the Seismic Hazards Investigation of Puget Sound (SHIPS). As part of a larger initiative to better understand laterAuthorsThomas M. Brocher, Tom Parsons, Ken C. Creager, Robert S. Crosson, Neill P. Symons, George D. Spence, Barry C. Zelt, Philip T.C. Hammer, Roy D. Hyndman, David C. Mosher, Anne M. Tréhu, Kate C. Miller, Uri S. ten Brink, Michael A. Fisher, Thomas L. Pratt, Marcos G. Alvarez, Bruce C. Beaudoin, Keith E. Louden, Craig S. WeaverNon-USGS Publications**
1992, by Parsons, T. et al., Department of Geophysics, Stanford University1992, by Parsons, T., et al., Department of Geophysics, Stanford University1991, by Howie, J.M., et al., Department of Geophysics, Stanford University1991, by Parsons, T., and Thompson, G.A., Department of Geophysics, Stanford University**Disclaimer: The views expressed in Non-USGS publications are those of the author and do not represent the views of the USGS, Department of the Interior, or the U.S. Government.
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*Disclaimer: Listing outside positions with professional scientific organizations on this Staff Profile are for informational purposes only and do not constitute an endorsement of those professional scientific organizations or their activities by the USGS, Department of the Interior, or U.S. Government