Three-dimensional finite element analysis of post-seismic deformation following the 1992 M7.3 Landers and 1999 M7.1 Hector Mine, California earthquakes inferred from InSAR and GPS observations

Post-seismic surface displacements in the 14 and 7 years following the 1992 Mw 7.3 Landers and 1999 Mw 7.1 Hector Mine earthquakes, respectively, demonstrate a previously unrecognized broad pattern of transient deformation throughout southern California and into Nevada. Based on GPS data compared to 3D finite element models Freed et al. [2007]* attribute these broad displacements to upper mantle viscoelastic relaxation following these earthquakes. Significant transient variations are also revealed by Synthetic Aperture Radar (SAR) data that we integrate with the GPS data to obtain both accurate and fine spatial characterization of ground deformation. We compute the expected far-field post-seismic Hector Mine ground deformation with a 3D Finite Element Method (FEM) model using the parallel code PyLith. The numerical model takes into account heterogeneous medium properties. The post-seismic effects of the Landers earthquake are also included in the model. The complex geometry of the Landers and Hector Mine ruptures are determined based on the field mapping data and inversion of co-seismic geodetic data. To explain post-seismic deformation following the Landers and Hector Mine earthquakes we examine two possible mechanisms including non-elastic relaxation as well as afterslip models. The results for a layered viscoelastic structure are compared with those obtained using power-law rheologies. The comparisons between the different models could allow us to discover the dominant mechanism that best explains the post-seismic deformation, and could also provide a better understanding of the rheological properties of the lithosphere. *Freed, A. M., R. Bürgmann, and T. Herring (2007), Far-reaching transient motions after Mojave earthquakes require broad mantle flow beneath a strong crust, Geophys. Res. Lett., 34, L19302, doi:10.1029/2007GL030959.