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, Moffett Field, 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, 2019-2022
Member: Executive Committee, Council of Senior Science Advisors (COSSA), 2015-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 2005-2014
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
Filter Total Items: 120
Crustal structure of the Cascadia fore arc of Washington Crustal structure of the Cascadia fore arc of Washington
No abstract available.
Authors
Tom Parsons, Richard J. Blakely, Thomas M. Brocher, Nikolas I. Christensen, Michael A. Fisher, Ernst Flueh, Fiona Kilbride, James H. Luetgert, Kate Miller, Uri S. ten Brink, Anne M. Trehu, Ray E. Wells
Significance of stress transfer in time-dependent earthquake probability calculations Significance of stress transfer in time-dependent earthquake probability calculations
A sudden change in stress is seen to modify earthquake rates, but should it also revise earthquake probability? Data used to derive input parameters permits an array of forecasts; so how large a static stress change is require to cause a statistically significant earthquake probability change? To answer that question, effects of parameter and philosophical choices are examined through...
Authors
T. Parsons
A hypothesis for delayed dynamic earthquake triggering A hypothesis for delayed dynamic earthquake triggering
It's uncertain whether more near-field earthquakes are triggered by static or dynamic stress changes. This ratio matters because static earthquake interactions are increasingly incorporated into probabilistic forecasts. Recent studies were unable to demonstrate all predictions from the static-stress-change hypothesis, particularly seismicity rate reductions. However, current dynamic...
Authors
T. Parsons
Recalculated probability of M ≥ 7 earthquakes beneath the Sea of Marmara, Turkey Recalculated probability of M ≥ 7 earthquakes beneath the Sea of Marmara, Turkey
New earthquake probability calculations are made for the Sea of Marmara region and the city of Istanbul, providing a revised forecast and an evaluation of time-dependent interaction techniques. Calculations incorporate newly obtained bathymetric images of the North Anatolian fault beneath the Sea of Marmara [Le Pichon et al., 2001; Armijo et al., 2002]. Newly interpreted fault...
Authors
T. Parsons
Structure and mechanics of the Hayward-Rodgers Creek Fault step-over, San Francisco Bay, California Structure 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...
Authors
T. Parsons, R. Sliter, E.L. Geist, R.C. Jachens, B. E. Jaffe, A. Foxgrover, P. E. Hart, J. McCarthy
Seismic evidence for widespread serpentinized forearc upper mantle along the Cascadia margin 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...
Authors
T.M. Brocher, T. Parsons, A.M. Trehu, C.M. Snelson, M. A. Fisher
Crustal structure of the coastal and marine San Francisco Bay region, California Crustal 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...
Global Omori law decay of triggered earthquakes: Large aftershocks outside the classical aftershock zone Global 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...
Authors
Tom Parsons
Post-1906 stress recovery of the San Andreas fault system calculated from three-dimensional finite element analysis Post-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...
Authors
Tom Parsons
Nearly frictionless faulting by unclamping in long-term interaction models Nearly 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
Authors
T. Parsons
Very different crustal response to extreme extension in the southern Basin and Range and Colorado Plateau transition Very 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...
Authors
Tom Parsons, Jill McCarthy, George A. Thompson
A simple algorithm for sequentially incorporating gravity observations in seismic traveltime tomography A 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...
Authors
T. Parsons, R.J. Blakely, T.M. Brocher
Non-USGS Publications**
1992, by Parsons, T. et al., Department of Geophysics, Stanford University
1992, by Parsons, T., et al., Department of Geophysics, Stanford University
1991, by Howie, J.M., et al., Department of Geophysics, Stanford University
1991, 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.
Science and Products
Filter Total Items: 120
Crustal structure of the Cascadia fore arc of Washington Crustal structure of the Cascadia fore arc of Washington
No abstract available.
Authors
Tom Parsons, Richard J. Blakely, Thomas M. Brocher, Nikolas I. Christensen, Michael A. Fisher, Ernst Flueh, Fiona Kilbride, James H. Luetgert, Kate Miller, Uri S. ten Brink, Anne M. Trehu, Ray E. Wells
Significance of stress transfer in time-dependent earthquake probability calculations Significance of stress transfer in time-dependent earthquake probability calculations
A sudden change in stress is seen to modify earthquake rates, but should it also revise earthquake probability? Data used to derive input parameters permits an array of forecasts; so how large a static stress change is require to cause a statistically significant earthquake probability change? To answer that question, effects of parameter and philosophical choices are examined through...
Authors
T. Parsons
A hypothesis for delayed dynamic earthquake triggering A hypothesis for delayed dynamic earthquake triggering
It's uncertain whether more near-field earthquakes are triggered by static or dynamic stress changes. This ratio matters because static earthquake interactions are increasingly incorporated into probabilistic forecasts. Recent studies were unable to demonstrate all predictions from the static-stress-change hypothesis, particularly seismicity rate reductions. However, current dynamic...
Authors
T. Parsons
Recalculated probability of M ≥ 7 earthquakes beneath the Sea of Marmara, Turkey Recalculated probability of M ≥ 7 earthquakes beneath the Sea of Marmara, Turkey
New earthquake probability calculations are made for the Sea of Marmara region and the city of Istanbul, providing a revised forecast and an evaluation of time-dependent interaction techniques. Calculations incorporate newly obtained bathymetric images of the North Anatolian fault beneath the Sea of Marmara [Le Pichon et al., 2001; Armijo et al., 2002]. Newly interpreted fault...
Authors
T. Parsons
Structure and mechanics of the Hayward-Rodgers Creek Fault step-over, San Francisco Bay, California Structure 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...
Authors
T. Parsons, R. Sliter, E.L. Geist, R.C. Jachens, B. E. Jaffe, A. Foxgrover, P. E. Hart, J. McCarthy
Seismic evidence for widespread serpentinized forearc upper mantle along the Cascadia margin 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...
Authors
T.M. Brocher, T. Parsons, A.M. Trehu, C.M. Snelson, M. A. Fisher
Crustal structure of the coastal and marine San Francisco Bay region, California Crustal 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...
Global Omori law decay of triggered earthquakes: Large aftershocks outside the classical aftershock zone Global 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...
Authors
Tom Parsons
Post-1906 stress recovery of the San Andreas fault system calculated from three-dimensional finite element analysis Post-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...
Authors
Tom Parsons
Nearly frictionless faulting by unclamping in long-term interaction models Nearly 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
Authors
T. Parsons
Very different crustal response to extreme extension in the southern Basin and Range and Colorado Plateau transition Very 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...
Authors
Tom Parsons, Jill McCarthy, George A. Thompson
A simple algorithm for sequentially incorporating gravity observations in seismic traveltime tomography A 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...
Authors
T. Parsons, R.J. Blakely, T.M. Brocher
Non-USGS Publications**
1992, by Parsons, T. et al., Department of Geophysics, Stanford University
1992, by Parsons, T., et al., Department of Geophysics, Stanford University
1991, by Howie, J.M., et al., Department of Geophysics, Stanford University
1991, 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.
*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