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A Geodetic Constraint on Seismic Velocity Changes in Fault Damage Zones

Seismic velocities are known to reduce around the vicinity of a fault. This reduction is often characterized by the existence of a fault damage zone, the structure and property of which, indicate the maturity of the fault and affect future co-seismic rupture process. There has been lots of seismologic studies that reported such reduction and vp/vs ratio changes along many faults. Here we present a geodetic approach on constraining the structure and velocity changes in fault damage zones. When earthquake stress release causes compliant deformation on its nearby faults, one could detect these motions with high-resolution InSAR acquisitions. With the deformation profiles, the width of the fault damage zones could be directly measured. Using a fault slip model, we could then estimate the strain conditions across these compliant faults. We input these into a finite element fault zone model to fit the fault-parallel and vertical deformation profile by changing the depth extent of the damage zone, its shear modulus reduction and Poisson’s ratio. The depth extent is constrained by the decay of the deformation profile outside of the damage zone, while the horizontal amplitude is controled by the shear modulus reduction. Given these two parameters, one could further change the p-wave velocity to get the right amplitude for vertical deformation. Compared to seismic analysis that is usually limited by the resolution, this geodetic approach is mostly definitive.

Session: Fault Damage Zones: What We Know and Do Not II

Type: Oral

Room: Grand A

Date: 4/20/2022

Presentation Time: 05:00 PM Pacific

Presenting Author: Xiaohua Xu

Student Presenter: No

Additional Authors