Vp/Vs tomography in the southern California plate boundary region using body- and surface-wave traveltime data

Hongjian Fang, Huajian Yao, Haijiang Zhang, Clifford Thurber, Yehuda Ben-Zion, & Robert D van der Hilst

Published October 31, 2018, SCEC Contribution #8909

Vp/Vs models provide important complementary information to Vp and Vs models, relevant to lithology, rock damage, partial melting, water saturation, etc. However, seismic tomography using body-wave traveltime data from local or regional earth- quakes does not constrain Vp/Vs well due to the different resolution of Vp and Vs models, with the Vp models usually better constrained than Vs. Since surface- wave data are most sensitive to Vs, which leads to complementary strengths of body-wave data, we jointly invert body- and surface-wave data to better resolve the Vp/Vs models. In order to show the robustness of our joint inversion method, we compare the results to other approaches, including dividing Vp by Vs models, and Vp/Vs parameterization with body-wave or both body- and surface-wave data, using synthetic data and real data from the southern California plate boundary region. We confirm that Vp/Vs models from body-wave inversion obtained by divi- sion tend to include artifacts, even when both Vp and Vs models seem reasonable. The joint inversion with Vp/Vs parameterization is found to improve the Vp/Vs ratio model significantly and the resultant Vp/Vs model shows more geologically consistent features, such as high Vp/Vs along fault traces at shallow depths likely indicating fault-related damage. The Vp/Vs model also exhibits contrasts at in- termediate depths along the Peninsular Range compositional boundary, and high Vp/Vs in the lower crust near the Salton Sea region correlated with high heat flow data and may indicate partial melting. The improved Vp/Vs as well as individual Vp and Vs models are useful for earthquake relocation, high-resolution Moho depth imaging, and interpretation of other data and tectonic evolution in the region.

Key Words
Joint inversion, seismic tomography, body waves, surface waves and free oscillations

Citation
Fang, H., Yao, H., Zhang, H., Thurber, C., Ben-Zion, Y., & van der Hilst, R. (2018). Vp/Vs tomography in the southern California plate boundary region using body- and surface-wave traveltime data. Geophysical Journal International,. doi: 10.1093/gji/ggy458.