Surface-wave and Body-wave Tomography for Central California

Avinash Nayak, Clifford H. Thurber, Hongjian Fang, Xiangfang Zeng, & Haijiang Zhang

In Preparation December 11, 2018, SCEC Contribution #8969

We present results of surface-wave and body-wave tomography efforts in central California in the Southern California Earthquake Center's Central California Seismic Project study area. We derive empirical Green's functions from multi-component cross-correlations of ambient seismic noise recorded by temporary and permanent seismic stations during specific epochs between 1997 and 2017. We invert Rayleigh-wave group velocity dispersion measurements extracted from the noise cross-correlations for group velocity maps at periods ~4.8 s to 16 s, which provide unprecedented constraints on the crustal shear-wave velocity, especially in the Great Valley and Sierra Nevada regions. A 3-D Vs model is assembled from the 1D Vs versus depth profiles extracted from the group velocity maps at each model node. Prominent features observed in the resulting seismic velocity models are: the Central Valley with near-surface Vs as low as ~ 800 m/s, the high-velocity Great Valley Ophiolite Body in the lower crust, high upper crustal velocities in the Sierra Nevada region and the velocity contrast across the San Andreas fault. We also establish a database of P-wave and S-wave arrival times automatically picked on records of local earthquakes (M > 2.4) recorded by permanent and temporary stations for further insights into the velocity structure. The earthquake dataset is combined with all available explosion data in the study region. We invert the body-wave travel arrival times for Vp and Vs models, simultaneously refining the earthquake hypocenters and origin times. We also present initial efforts towards a joint inversion of the body-wave and surface-wave datasets.

Citation
Nayak, A., Thurber, C. H., Fang, H., Zeng, X., & Zhang, H. (2018, 12). Surface-wave and Body-wave Tomography for Central California. Oral Presentation at American Geophysical Union.

Related Projects & Working Groups
CCSP