Discipline: Ecology Environmental and Earth Sciences
Subcategory: Geosciences and Earth Sciences
Carlos D. Gomez - California State University Northridge
Co-Author(s): Lennin Escobar and Dayanthie Weeraratne, California State University Northridge Monica Kohler, Caltech, Pasadena, CA Fan-Chi Lin, University of Utah, Salt Lake City, UT Mark Legg, Legg Geophysical, Huntington Beach, CA Natsumi Shintaku, Brown University, Providence, RI
Introduction: The California continental margin is a site vulnerable to both locally generated tsunamis from local offshore seismic activity as well as distant tsunamis generated from around the Pacific Rim by large seismic events at plate boundaries such as the 2011 Tohoku earthquake. The site of a major transform plate boundary, this continental margin is composed of complex topography and tectonic stress fields that affect coseismic wave propagation, tsunami wave propagation and ongoing deformational strain in the lithospheric plate.
Methods: Data obtained by ALBACORE’s (Asthenospheric and Lithospheric Broadband Architecture from the California Offshore Region Experiment) ocean bottom seismometers (OBSs) and the CISN (California Integrated Seismic Network) are analyzed for tsunami-wave arrivals at periods 200 – 3000s. Azimuthal anisotropy of Rayleigh waves from passive source teleseismic events at periods 16 – 78s are used to resolve subsurface lithospheric structure. We invert Rayleigh wave data for shear wave velocity structure and three-dimensional seismic anisotropy in three regions within our study area; the sea floor, the continent, and the California Borderlands which bridges the first 2 regions.
Results: Preliminary results show that seismic anisotropy is resolved in multiple layers and can be used to determine the Moho, lithosphere-asthenosphere boundary (LAB) and remnant underplated slabs. Anisotropic structure within oceanic lithosphere identifies both remnant structure frozen in from formational history as well as active tectonic motion and deformation today. Our 8 regions show 2 layer anisotropy and we are able to resolve the base of the lithosphere around 60 km at seafloor to over 100 km moving landward to the Garlock fault.
Conclusions and future research questions: New offshore bathymetry obtained from the ALBACORE project and the influence of the seafloor surface on tsunami wave propagation will be presented in future meetings. We wish to further correlate the seismic subsurface anisotropy, presented here, with natural hazards such as tsunamis and earthquakes.
Funder Acknowledgement(s): National Science Foundation
Faculty Advisor: Dayanthie S. Weeraratne, firstname.lastname@example.org
Role: My job as an undergraduate research assistant was organizing and processing the seismic data used in this project, as well as interpreting it and comparing our results with the results of other research done in this area. More specifically, I ran the Rayleigh wave surface inversions using Fortran and Matlab code to obtain shear wave velocities and seismic anisotropy for our 8 regions. I organized our data into charts and researched the past 100 million years into southern California's tectonic history. Finally, I collaborated with other students and researchers to draw possible conclusions (i) on what tectonic models best fit our results and (ii) what this may mean in hazard mitigation and future tectonic deformation.