ACTIVE RESEARCH PROJECTS:
-
Block rotations and fault slip rates in the eastern California shear zone
-
Subduction zone locking and slip patterns (esp. Cascadia, Japan)
-
Network design for seafloor geodetic observations
-
Slip partitioning in subduction zones between megathrust and strike-slip surface faults
-
Mapping historical seafloor bathymetry to estimate subduction deformation
RECENT RESEARCH PROJECTS:
GEODETIC SLIP RATES IN CALIFORNIA
Geodetic observations are included in the 2014 U.S. Geological Survey (USGS) National Seismic Hazard Model (NSHM) and in the Third Uniform California Earthquake Rupture Forecast (UCERF3), but significant challenges and questions remain. For example, how do we correctly assimilate the large and potentially disparate suite of published and ongoing tectonic geodesy studies? Can we reduce apparent discrepancies between geologically and geodetically estimated fault slip rates? How might we reconcile the apparently large amount of observed deformation that does not appear to be associated with major faults? This project is a quantitative attempt to address these questions.
EASTERN CALIFORNIA SHEAR ZONE
Taking advantage of a new approach for estimating fault slip rates from GPS observations, we address discrepancies in the eastern California shear zone between slip rates estimated from geologic observations and those based on GPS measurements. A novel modeling method considers many potentially active faults in a fault geometry that may be considered analogous to distributed deformation, and finds that eastern California shear zone deformation is well described by 10 microplates. Discrepancies with geologic slip rates appear to be persistent, with large discrepancies on the Calico and Garlock faults. This result may be inconsistent with the presence of distributed off-fault deformation in the eastern California shear zone. Understanding the localized discrepancies on the Calico and Garlock faults may hold important clues for understanding how fault systems deform and evolve in time, and for earthquake hazard in eastern California.
WESTERN US BLOCKS
Tools from the applied mathematics field of compressed sensing, often used in image and signal processing, may be applied to models of plate boundary deformation to constrain fault system behavior and help identify appropriate modeling assumptions. Beginning with a dense array of tectonic micro-plates bounded by mapped faults in North America, these methods can detect coherent motions of groups of micro-plates behaving as larger active blocks, effectively quantifying the complexity of North America deformation.
SPARSE EARTHQUAKE SLIP
Earthquake slip models are often regularized by assuming that slip varies smoothly in space, which may artificially smear slip estimates beyond physical boundaries. As an alternative to smooth regularization, the applied mathematics field of compressed sensing provides a suite of methods for recovering sparse solutions. Applied to GPS observations of the M = 9.0 2011 Tohoku earthquake, compressed sensing algorithms enable imaging of spatially localized slip during and following the earthquake, and identification of a sharp boundary between coseismic and postseismic slip.
SAN FRANCISCO BAY AREA ACTIVE TECTONICS
The Hayward fault in the east San Francisco Bay Area is considered the most likely fault to generate a major earthquake in the next 30 years. A partially locked portion of the fault is spatially correlated with the mapped surface trace of the 1869 MW=6.9-7.0 Hayward earthquake and adjacent to gabbroic fault surfaces.
