Joint inversion for 1-D crustal seismic S- and P-wave velocity structures with interfaces and its application to the Wabash Valley Seismic Zone

Interfaces are important part of Earth's layering structure. Here, we developed a new model parametrization and iterative linearized inversion method that determines 1-D crustal velocity structure using surfacewave dispersion, teleseismic P-wave receiver functions and Ps and PmP traveltimes. Unlike previous joint inversion methods, the new model parametrization includes interface depths and layer Vp/Vs ratios so that smoothness constraint can be conveniently applied to velocities of individual layers without affecting the velocity discontinuity across the interfaces. It also allows adding interface-related observation such as traveltimes of Ps and PmP in the joint inversion to eliminate the trade-off between interface depth and Vp/Vs ratio and therefore to reduce the uncertainties of results. Numerical tests show that the method is computationally efficient and the inversion results are robust and independent of the initial model. Application of the method to a dense linear array across the Wabash Valley Seismic Zone (WVSZ) produced a high-resolution crustal image in this seismically active region. The results show a 51-55-km-thick crust with a mid-crustal interface at 14-17 km. The crustal Vp/Vs ratio varies from 1.69 to 1.90. There are three pillow-like, similar to 100 km apart high-velocity bodies sitting at the base of the crust and directly above each of them are a low-velocity anomaly in the middle crust and a high-velocity anomaly in the upper crust. They are interpreted to be produced by mantle magmatic intrusions and remelting during rifting events in the end of the Precambrian. The current diffuse seismicity in the WVSZ might be rooted in this ancient distributed rifting structure.

Automated summary

Interfaces are significant in Earth's layering structure and a new model parametrization with iterative linearized inversion method has been developed to determine 1-D crustal velocity structure efficiently. The method applied to dense linear array across the Wabash Valley Seismic Zone produced high-resolution crustal image, revealing crustal features and potential geological processes in the area.