Interseismic Deformation in the Northern Andean Subduction Zone

My latest project studies interseismic deformation and locking in the northern Chile-Peru subduction zone using Interferometric Synthetic Aperture Radar (InSAR) data. This includes analysis of coseismic displacements from the 2001 and 2007 Peru earthquakes and modeling of post-seismic and interseismic fault creep in this region using Bayesian methods. A long-term goal of this project is to enhance understanding of seismic hazard in the Arica gap region of southern Peru and northern Chile.

I am also working on a new version of the Generic InSAR Analysis Toolbox (GIAnT 2.0), which will update the InSAR time-series analysis tools currently provided in GIAnT.

Collaborators:

Mark Simons (advisor, Caltech/JPL); Heresh Fattahi (JPL); Piyush Agram (JPL); Ollie Stephenson (Caltech)

Coupling and applications of Distributed Acoustic Sensing (DAS) for earthquake seismology

While several recent studies have shown the promising broadband sensitivity of DAS strain measurements for earthquake seismology applications, a number of outstanding problems remain. One aspect of this project focuses on modeling the effects of variable elastic coupling of the fiber-optic cable to the ground and developing a method to separate coupling-related resonances or changes in sensitivty from seismic site effects, which are an important product of urban seismic monitoring. Another aspect of this project considers ultra-low frequency strain signals (e.g. Earth tides) and seeks to quantify the potential value of DAS as a geodetic instrument.

Collaborators:

Zhongwen Zhan (advisor, Caltech)

Neotectonics of the Southern California Continental Borderland

The tortuous tectonic history of the Southern California Continental Borderland has resulted in complex offshore fault zones, which have been poorly studied despite their tremendous significance to quanitifying seismic hazard in the region. The Anacapa-Dume Fault, a sinistral-oblique thrust system offshore Point Dume, connects to the Santa Monica and Raymond Faults. Our study integrating single- and multi-channel seismic, multibeam backscatter and bathymetry, and ROV photographs at Sycamore Knoll constrains latest Quaternary slip on the Anacapa-Dume Fault.

The Santa Cruz-Catalina Ridge and Long Point fault systems offshore Catalina Island control the tilting of the Catalina block since at least Pliocene time. Our study integrating multi-channel seismic, U/Th ages from fossil corals, and radiocarbon ages from fossil mollusks identifies the timing of Quaternary tsunamogenic landslides offshore Los Angeles and constrains the rate of subsidence of Catalina Island.

Collaborators:

Chris Castillo (Stanford); Simon Klemperer (Stanford)

Publications:

Williams, E.F., Castillo, C.M., Klemperer, S.L., Raineault, N., and Gee, L., in review. Sycamore Knoll: A wave-planed pop-up structure in a sinistral-oblique fault system, Southern California Continental Borderland. Deep Sea Research, Part II: Telepresence Results

Williams, E.F., Castillo, C.M., Klemperer, S.L., Raineault, N., and Gee, L., 2017, A new estimate of latest Quaternary slip on the Anacapa-Dume Fault at Sycamore Knoll, Southern California Continental Borderland. Poster presented at the Southern California Earthquake Center (SCEC) Annual Meeting, September 2017.

Castillo, C.M., Klemperer, S.L., Williams, E.F., Legg, M.R., and Francis, R.D., 2015, Tsunamogenic landslides and marine paleoseismology: applications of the submerged marine terrace record, Santa Catalina Island, Southern California Borderland. Talk presented at the American Geophysical Union (AGU) Fall Meeting, December 2015.

Williams, E.F., Castillo, C.M., Klemperer, S.L., Maher, K.M., Francis, R.D., and Legg, M.R., 2015, Preliminary results of marine paleoseismology from MCS, CHIRP, and coring off Catalina Island. Poster presented at the Southern California Earthquake Center (SCEC) Annual Meeting, September 2015.

Ambient Noise Interferometry with DAS

Seismic imaging in urban areas is essential for structural engineering and earthquake hazard quantification. Distributed acoustic sensing (DAS) technology promises to decrease the cost of urban passive seismic imaging by repurposing unused "dark" fiber optic cables as seismic recording arrays. We utilized ambient noise recordings from pilot DAS arrays in Richmond, CA, and Fairbanks, AK, to develop an automated time-domain processing workflow that efficiently removes coherent sound generated by transportation infrastructure operating near the array. Application of our method to ambient noise interferometry showed significant improvement in the degree of convergence of the fundamental mode Rayleigh wave.

Collaborators:

Eileen Martin (Stanford); Biondo Biondi (Stanford)

Publications:

Williams, E.F. and Martin, E.R., 2016, Detection and removal of coherent anthropogenic noise from passive seismic data. SEP Report 165, pp. 153-164.

Williams, E.F., Martin, E.R., Biondi, B., Lindsey, N.J., Ajo-Franklin, J.B., Wagner, A.M., Bjella, K.L., Daley, T.M., Dou, S., Freifeld, B.M., Robertson, M., and Ulrich, C., 2016, Quality of Green's functions improved by automatic detection and removal of coherent structural noise. Poster presented at the American Geophysical Union (AGU) Fall Meeting, December 2016.

U-Th Open System Modeling

In U-Th disequilibrium dating, open system behavior of marine biogenic carbonate often makes accurate age determination impossible. This is particularly true for fossil mollusks and solitary corals. We are developing an open-source Matlab toolbox that paramaterizes and models the U-Th decay system using finite difference methods for both closed and open system behavior.

Collaborators:

Kate Maher (Stanford), Karrie Weaver (Stanford)