Eikonal Tomography of the Southern California Plate Boundary Region

Hongrui Qiu, Yehuda Ben-Zion, & Fan-Chi Lin

Published August 15, 2017, SCEC Contribution #7720, 2017 SCEC Annual Meeting Poster #037

We use eikonal tomography to derive directionally-dependent phase and group velocities of surface waves sensitive to the approximate depth range 1-20 km for the plate boundary region in southern CA. Seismic noise data recorded by 346 stations in the area provide a spatial coverage with ~5-25 km typical station spacing and period range of 1-20 s. Noise cross-correlations are calculated for all 9 components data recorded in year 2014. Rayleigh and Love waves group and phase travel times are derived for each station pair using frequency-time analysis. All available phase and group travel time measurements with sufficient signal to noise ratio are used to construct travel time maps for virtual sources located at each station. By solving the eikonal equation, local propagation directions are evaluated as the normal vectors of the phase travel time contour at each location for each virtual source. The phase and group slowness are then estimated as the first order spatial derivative of the corresponding travel time along the propagation direction. Isotropic phase and group velocities, 2-psi azimuthal anisotropy and their uncertainties between 2 and 15 s period are determined statistically using measurements from different virtual sources. The obtained phase and group dispersions of Rayleigh and Love waves are then jointly inverted on a 6 x 6 km2 grid for 1D piecewise shear wave velocity structures. Clear velocity contrasts and low velocity zones are seen for the San Andreas, San Jacinto, Elsinore and Garlock faults. We also find 2-psi azimuthal anisotropy with fast directions parallel to geometrically-simple fault sections. Radial anisotropy is also investigated by inverting dispersion data from Rayleigh and Love waves separately. Updated results will be presented in the meeting.

Key Words
Eikonal tomography, Surface wave, Anisotropy

Qiu, H., Ben-Zion, Y., & Lin, F. (2017, 08). Eikonal Tomography of the Southern California Plate Boundary Region. Poster Presentation at 2017 SCEC Annual Meeting.

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