Brad Aagaard
Brad Aagaard is a research scientist in the Earthquake Hazards Program.
Ground-motion modeling
- Animations of ground shaking from computer simulations of earthquakes.
- 3D Geologic and Seismic Velocity Model of the San Francisco Bay Region
Software
PyLith crustal deformation modeling software, Computational Infrastructure for Geodynamics.
Professional Experience
Research Geophysicist, USGS, 2003-present
USGS Mendenhall Postdoctoral Scholar, 2001-2003
Education and Certifications
Ph.D., Civil Engineering, California Institute of Technology, 2000
M.S., Civil Engineering, California Institute of Technology, 1995
B.S., Engineering, Harvey Mudd College, 1994
Science and Products
Filter Total Items: 46
Constraining fault constitutive behavior with slip and stress heterogeneity
We study how enforcing self-consistency in the statistical properties of the preshear and postshear stress on a fault can be used to constrain fault constitutive behavior beyond that required to produce a desired spatial and temporal evolution of slip in a single event. We explore features of rupture dynamics that (1) lead to slip heterogeneity in earthquake ruptures and (2) maintain...
Authors
Brad T. Aagaard, T. H. Heaton
Ground-motion modeling of the 1906 San Francisco earthquake, part I: Validation using the 1989 Loma Prieta earthquake
We compute ground motions for the Beroza (1991) and Wald et al. (1991) source models of the 1989 magnitude 6.9 Loma Prieta earthquake using four different wave-propagation codes and recently developed 3D geologic and seismic velocity models. In preparation for modeling the 1906 San Francisco earthquake, we use this well-recorded earthquake to characterize how well our ground-motion...
Authors
Brad T. Aagaard, T. M. Brocher, D. Dolenc, D. Dreger, R.W. Graves, S. Harmsen, S. Hartzell, S. Larsen, M.L. Zoback
Visualizing the ground motions of the 1906 San Francisco earthquake
With advances in computational capabilities and refinement of seismic wave-propagation models in the past decade large three-dimensional simulations of earthquake ground motion have become possible. The resulting datasets from these simulations are multivariate, temporal and multi-terabyte in size. Past visual representations of results from seismic studies have been largely confined to...
Authors
A. Chourasia, S. Cutchin, Brad T. Aagaard
Basin structure beneath the Santa Rosa Plain, Northern California: Implications for damage caused by the 1969 Santa Rosa and 1906 San Francisco earthquakes
Regional gravity data in the northern San Francisco Bay region reflect a complex basin configuration beneath the Santa Rosa plain that likely contributed to the significant damage to the city of Santa Rosa caused by the 1969 M 5.6, 5.7 Santa Rosa earthquakes and the 1906 M 7.9 San Francisco earthquake. Inversion of these data indicates that the Santa Rosa plain is underlain by two...
Authors
D.K. McPhee, V. E. Langenheim, S. Hartzell, R. J. McLaughlin, Brad T. Aagaard, R.C. Jachens, C. McCabe
Implications for prediction and hazard assessment from the 2004 Parkfield earthquake
Obtaining high-quality measurements close to a large earthquake is not easy: one has to be in the right place at the right time with the right instruments. Such a convergence happened, for the first time, when the 28 September 2004 Parkfield, California, earthquake occurred on the San Andreas fault in the middle of a dense network of instruments designed to record it. The resulting data...
Authors
W. H. Bakun, Brad T. Aagaard, B. Dost, William L. Ellsworth, Jeanne L. Hardebeck, Ruth A. Harris, C. Ji, Malcolm J. S. Johnston, John O. Langbein, James J. Lienkaemper, Andrew J. Michael, Jessica R. Murray, R.M. Nadeau, P.A. Reasenberg, M.S. Reichle, Evelyn A. Roeloffs, A. Shakal, Robert W. Simpson, F. Waldhauser
Teleseismic body waves from dynamically rupturing shallow thrust faults: Are they opaque for surface-reflected phases?
We investigate whether a shallow-dipping thrust fault is prone to waveslip interactions via surface-reflected waves affecting the dynamic slip. If so, can these interactions create faults that are opaque to radiated energy? Furthermore, in this case of a shallow-dipping thrust fault, can incorrectly assuming a transparent fault while using dislocation theory lead to underestimates of...
Authors
D.E. Smith, Brad T. Aagaard, T. H. Heaton
Dynamic rupture modeling of the transition from thrust to strike-slip motion in the 2002 Denali fault earthquake, Alaska
We use three-dimensional dynamic (spontaneous) rupture models to investigate the nearly simultaneous ruptures of the Susitna Glacier thrust fault and the Denali strike-slip fault. With the 1957 Mw 8.3 Gobi-Altay, Mongolia, earthquake as the only other well-documented case of significant, nearly simultaneous rupture of both thrust and strike-slip faults, this feature of the 2002 Denali...
Authors
Brad T. Aagaard, G. Anderson, K.W. Hudnut
Effects of fault dip and slip rake angles on near-source ground motions: Why rupture directivity was minimal in the 1999 Chi-Chi, Taiwan, earthquake
We study how the fault dip and slip rake angles affect near-source ground velocities and displacements as faulting transitions from strike-slip motion on a vertical fault to thrust motion on a shallow-dipping fault. Ground motions are computed for five fault geometries with different combinations of fault dip and rake angles and common values for the fault area and the average slip. The...
Authors
Brad T. Aagaard, J. F. Hall, T. H. Heaton
Near-source ground motions from simulations of sustained intersonic and supersonic fault ruptures
We examine the long-period near-source ground motions from simulations of M 7.4 events on a strike-slip fault using kinematic ruptures with rupture speeds that range from subshear speeds through intersonic speeds to supersonic speeds. The strong along-strike shear-wave directivity present in scenarios with subshear rupture speeds disappears in the scenarios with ruptures propagating...
Authors
Brad T. Aagaard, T. H. Heaton
Fault interactions and large complex earthquakes in the Los Angeles area
Faults in complex tectonic environments interact in various ways, including triggered rupture of one fault by another, that may increase seismic hazard in the surrounding region. We model static and dynamic fault interactions between the strike-slip and thrust fault systems in southern California. We find that rupture of the Sierra Madre-Cucamonga thrust fault system is unlikely to...
Authors
Greg Anderson, Brad T. Aagaard, Ken Hudnut
Science and Products
Filter Total Items: 46
Constraining fault constitutive behavior with slip and stress heterogeneity
We study how enforcing self-consistency in the statistical properties of the preshear and postshear stress on a fault can be used to constrain fault constitutive behavior beyond that required to produce a desired spatial and temporal evolution of slip in a single event. We explore features of rupture dynamics that (1) lead to slip heterogeneity in earthquake ruptures and (2) maintain...
Authors
Brad T. Aagaard, T. H. Heaton
Ground-motion modeling of the 1906 San Francisco earthquake, part I: Validation using the 1989 Loma Prieta earthquake
We compute ground motions for the Beroza (1991) and Wald et al. (1991) source models of the 1989 magnitude 6.9 Loma Prieta earthquake using four different wave-propagation codes and recently developed 3D geologic and seismic velocity models. In preparation for modeling the 1906 San Francisco earthquake, we use this well-recorded earthquake to characterize how well our ground-motion...
Authors
Brad T. Aagaard, T. M. Brocher, D. Dolenc, D. Dreger, R.W. Graves, S. Harmsen, S. Hartzell, S. Larsen, M.L. Zoback
Visualizing the ground motions of the 1906 San Francisco earthquake
With advances in computational capabilities and refinement of seismic wave-propagation models in the past decade large three-dimensional simulations of earthquake ground motion have become possible. The resulting datasets from these simulations are multivariate, temporal and multi-terabyte in size. Past visual representations of results from seismic studies have been largely confined to...
Authors
A. Chourasia, S. Cutchin, Brad T. Aagaard
Basin structure beneath the Santa Rosa Plain, Northern California: Implications for damage caused by the 1969 Santa Rosa and 1906 San Francisco earthquakes
Regional gravity data in the northern San Francisco Bay region reflect a complex basin configuration beneath the Santa Rosa plain that likely contributed to the significant damage to the city of Santa Rosa caused by the 1969 M 5.6, 5.7 Santa Rosa earthquakes and the 1906 M 7.9 San Francisco earthquake. Inversion of these data indicates that the Santa Rosa plain is underlain by two...
Authors
D.K. McPhee, V. E. Langenheim, S. Hartzell, R. J. McLaughlin, Brad T. Aagaard, R.C. Jachens, C. McCabe
Implications for prediction and hazard assessment from the 2004 Parkfield earthquake
Obtaining high-quality measurements close to a large earthquake is not easy: one has to be in the right place at the right time with the right instruments. Such a convergence happened, for the first time, when the 28 September 2004 Parkfield, California, earthquake occurred on the San Andreas fault in the middle of a dense network of instruments designed to record it. The resulting data...
Authors
W. H. Bakun, Brad T. Aagaard, B. Dost, William L. Ellsworth, Jeanne L. Hardebeck, Ruth A. Harris, C. Ji, Malcolm J. S. Johnston, John O. Langbein, James J. Lienkaemper, Andrew J. Michael, Jessica R. Murray, R.M. Nadeau, P.A. Reasenberg, M.S. Reichle, Evelyn A. Roeloffs, A. Shakal, Robert W. Simpson, F. Waldhauser
Teleseismic body waves from dynamically rupturing shallow thrust faults: Are they opaque for surface-reflected phases?
We investigate whether a shallow-dipping thrust fault is prone to waveslip interactions via surface-reflected waves affecting the dynamic slip. If so, can these interactions create faults that are opaque to radiated energy? Furthermore, in this case of a shallow-dipping thrust fault, can incorrectly assuming a transparent fault while using dislocation theory lead to underestimates of...
Authors
D.E. Smith, Brad T. Aagaard, T. H. Heaton
Dynamic rupture modeling of the transition from thrust to strike-slip motion in the 2002 Denali fault earthquake, Alaska
We use three-dimensional dynamic (spontaneous) rupture models to investigate the nearly simultaneous ruptures of the Susitna Glacier thrust fault and the Denali strike-slip fault. With the 1957 Mw 8.3 Gobi-Altay, Mongolia, earthquake as the only other well-documented case of significant, nearly simultaneous rupture of both thrust and strike-slip faults, this feature of the 2002 Denali...
Authors
Brad T. Aagaard, G. Anderson, K.W. Hudnut
Effects of fault dip and slip rake angles on near-source ground motions: Why rupture directivity was minimal in the 1999 Chi-Chi, Taiwan, earthquake
We study how the fault dip and slip rake angles affect near-source ground velocities and displacements as faulting transitions from strike-slip motion on a vertical fault to thrust motion on a shallow-dipping fault. Ground motions are computed for five fault geometries with different combinations of fault dip and rake angles and common values for the fault area and the average slip. The...
Authors
Brad T. Aagaard, J. F. Hall, T. H. Heaton
Near-source ground motions from simulations of sustained intersonic and supersonic fault ruptures
We examine the long-period near-source ground motions from simulations of M 7.4 events on a strike-slip fault using kinematic ruptures with rupture speeds that range from subshear speeds through intersonic speeds to supersonic speeds. The strong along-strike shear-wave directivity present in scenarios with subshear rupture speeds disappears in the scenarios with ruptures propagating...
Authors
Brad T. Aagaard, T. H. Heaton
Fault interactions and large complex earthquakes in the Los Angeles area
Faults in complex tectonic environments interact in various ways, including triggered rupture of one fault by another, that may increase seismic hazard in the surrounding region. We model static and dynamic fault interactions between the strike-slip and thrust fault systems in southern California. We find that rupture of the Sierra Madre-Cucamonga thrust fault system is unlikely to...
Authors
Greg Anderson, Brad T. Aagaard, Ken Hudnut