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Eikonal Tomography of the Southern California Plate Boundary Region

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

Published August 7, 2018, SCEC Contribution #8324, 2018 SCEC Annual Meeting Poster #100

We use eikonal tomography to derive directionally-dependent phase and group velocities of surface waves for the plate boundary region in southern CA sensitive to the approximate depth range 1-20 km. 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 wave and Love wave group and phase travel times are derived for each station pair using frequency-time analysis. For each common station, all available phase and group travel time measurements with sufficient signal to noise ratio and envelope peak amplitude are used to construct a travel time map for a virtual source at the common station location, respectively. By solving the eikonal equation, the propagation direction is evaluated as the normal vector at each location for each virtual source in the phase travel time map, and then phase and group velocities are estimated along the propagation direction. Isotropic phase and group velocities and 2- psi azimuthal anisotropy and their uncertainties for periods in the range 2-16 sec are determined statistically using measurements from different virtual sources. By using the CVM-S4.26 constructed in Lee et al. (2014) as starting model, the obtained phase and group dispersions of Rayleigh and Love waves are then jointly inverted on a 0.05° x 0.05° grid for local 1D piecewise shear wave velocity structures with the algorithm of Hermann (2014). The results are consistent with previous observations of Zigone et al. (2015) and other tomography results in the overlapping area. Compared with the CVM-S4.26, our final model is able to resolve structure above 5 km with better resolution and shows lower shear wave velocity in the top 5 km, particularly in areas such as basins and fault zones. The results also show clear velocity contrasts across the major faults, such as the San Andreas, San Jacinto, Elsinore and Garlock faults, and suggest that the San Andreas Fault southeast of San Gorgonio Pass is dipping to the northeast.

Key Words
Eikonal tomography, Surface wave

Qiu, H., Ben-Zion, Y., & Lin, F. (2018, 08). Eikonal Tomography of the Southern California Plate Boundary Region
. Poster Presentation at 2018 SCEC Annual Meeting.

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