Publications

Creep in the San Andreas Fault Observatory at Depth (SAFOD) drillhole is localized to two foliated gouges, the central deforming zone (CDZ) and southwest deforming zone (SDZ). The gouges consist of porphyroclasts of serpentinite and sedimentary rock dispersed in a foliated matrix of Mg-smectite clays that formed as a result of shearing-enhanced reactions between the serpentinite and quartzofeldspa

Surface creep rate, observed along five branches of the dextral San Andreas fault system in northern California, varies considerably from one section to the next, indicating that so too may the depth at which the faults are locked. We model locking on 29 fault sections using each section’s mean long‐term creep rate and the consensus values of fault width and geologic slip rate. Surface creep rate

Structure from Motion (SfM) generates high-resolution topography and coregistered texture (color) from an unstructured set of overlapping photographs taken from varying viewpoints, overcoming many of the cost, time, and logistical limitations of Light Detection and Ranging (LiDAR) and other topographic surveying methods. This paper provides the first investigation of SfM as a tool for mapping faul

We consider whether mm-scale earthquake-like seismic events generated in laboratory experiments are consistent with our understanding of the physics of larger earthquakes. This work focuses on a population of 48 very small shocks that are foreshocks and aftershocks of stick–slip events occurring on a 2.0 m by 0.4 m simulated strike-slip fault cut through a large granite sample. Unlike the larger s

In this study I consider the ground motions generated by 11 moderate (Mw4.0-5.6) earthquakes in the central and eastern United States that are thought or suspected to be induced by fluid injection. Using spatially rich intensity data from the USGS “Did You Feel It?” system, I show that the distance decay of intensities for all events is consistent with that observed for tectonic earthquakes in th

We investigate the ongoing seismicity in the Raton Basin and find that the deep injection of wastewater from the coal‐bed methane field is responsible for inducing the majority of the seismicity since 2001. Many lines of evidence indicate that this earthquake sequence was induced by wastewater injection. First, there was a marked increase in seismicity shortly after major fluid injection began in

On March 4, 2013, the City of Seattle and the U.S. Geological Survey (USGS) convened a workshop of 25 engineers and seismologists to provide recommendations to the City for the incorporation of amplification of earthquake ground shaking by the Seattle sedimentary basin in the design of tall buildings in Seattle. The workshop was initiated and organized by Susan Chang, a geotechnical engineer with

The stochastic method of simulating ground motions requires the specification of the shape and scaling with magnitude of the source spectrum. The spectral models commonly used are either single-corner-frequency or double-corner-frequency models, but the latter have no flexibility to vary the high-frequency spectral levels for a specified seismic moment. Two generalized double-corner-frequency ω2

The frequency-dependent effects of rupture propagation of the Parkfield, California earthquake (Sept. 28, 2004, M6) to the northwest along the San Andreas fault can be seen in acceleration records at UPSAR (USGS Parkfield Seismic Array) in at least two ways. First, we can see the effects of directivity in the acceleration traces at UPSAR, which is about 11.5 km from the epicenter. Directivity or t

Using seismic surface waves recorded with Earthscope's Transportable Array, we apply surface wave imaging to determine 3D seismic velocity in the crust and uppermost mantle. Our images span several Proterozoic and early Cambrian rift zones (Mid-Continent Rift, Rough Creek Graben—Rome trough, Birmingham trough, Southern Oklahoma Aulacogen, and Reelfoot Rift). While ancient rifts are generally assoc

The 1989 Loma Prieta earthquake interrupted several decades of seismic tranquility in the San Francisco Bay Area. It caused damage throughout the region and was a wakeup call to prepare for potentially even more damaging future quakes. Since 1989, the work of the U.S. Geological Survey and many other organizations has improved the understanding of the seismic threat in the Bay Area, promoted aware

We cannot yet predict large earthquakes in the short term with much reliability and skill, but the strong clustering exhibited in seismic sequences tells us that earthquake probabilities are not constant in time; they generally rise and fall over periods of days to years in correlation with nearby seismic activity. Operational earthquake forecasting (OEF) is the dissemination of authoritative info