Contact Info

Ethan F. Williams

Office: 358 South Mudd

Email: efwillia@gps.caltech.edu

Phone: (650) 888-7525

Mail:

MS 252-21
Seismo Lab, Caltech
1200 E. California Blvd.
Pasadena, CA 91125

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 (Caltech/JPL); Heresh Fattahi (JPL); Piyush Agram (JPL); Ollie Stephenson (Caltech)


Subduction Initiation South of New Zealand

The tectonic and geodynamic framework for the formation and evolution of subduction zones remains one of the least understood aspects of the plate tectonic cycle. At the Puysegur Trench, a bathymetric low in the Tasman Sea south of New Zealand, the Australian plate is thrust under the Pacific plate, representing the best natural laboratory to study active subduction initiation today. To the south, the down-dip extent of underthrusting is only a few kilometers at most, but to the north, seismicity down to 150 km depth indicates relatively mature subduction. In February-March 2018, we will sail on the R/V Marcus Langseth to collect seismic reflection/refraction profiles as well as gravity and magnetic data across the Puysegur Trench in order to investigate the structure and history of this nascent subduction zone.

Collaborators:

Mike Gurnis (Caltech); Joann Stock (Caltech); Erin Hightower (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)