Power-law viscoelastic flow of the lower Makran accretionary prism following the 2013 Baluchistan earthquake

Guo Cheng, & William D. Barnhart

Published August 14, 2021, SCEC Contribution #11400, 2021 SCEC Annual Meeting Poster #103 (PDF)

Accretionary prism is alternatively treated as an elastic, Coulomb prism or a system where permanent deformation is accommodated by faulting and folding of otherwise elastic materials. Recent geodetic observations of post-seismic surface deformation suggest that accretionary prisms may exhibit non-linear, bulk inelastic behavior on relatively short time-scales (months to years) as evidenced by viscoelastic relaxation following earthquakes. In this study, we examine the post-seismic deformation of the 2013 Baluchistan strike-slip earthquake in the Makran accretionary prism of southeast Pakistan to characterize the viscoelastic behavior of the wedge. We used Sentinel-1 SAR images from three viewing geometries to construct 7-year surface displacement timeseries following the earthquake. We constructed a 3-D finite element model of the Makran accretionary prism with the Hoshab fault plane hosting the 2013 Baluchistan earthquake. We used open-source FEM software PyLith to assign material properties to five different domains of the model. We varied the three main parameters controlling the viscoelastic properties of the lower prism (i.e. power-law exponent n, activation enthalpy Q, and pre-exponential constant A) while keeping the properties of other domains constant. We prescribed co-seismic slip distribution on the Hoshab fault and simulated the post-seismic viscoelastic deformation for 10 years. We compared the ~6000 forward-modeled post-seismic deformation timeseries to the observed InSAR timeseries and our results suggest that: 1. Viscoelastic relaxation alone of the Makran lower prism (8-40 km depth) explains most of the post-seismic surface deformation, and 2. viscoelastic relaxation requires power-law relaxation with parameters ranges of n = 3-4, Q = 100-140 kJ·mol^-1, and A = 10^-3-10^3 MPa^-n·s^-1. These results are consistent with post-seismic-triggered permanent deformation of the prism dominated by dislocation creep of quartz-rich materials under saturated condition.

Key Words
Subduction Zone, Post-seismic Deformation, Viscoelastic Relaxation, InSAR Timeseries, Finite Element Model

Citation
Cheng, G., & Barnhart, W. D. (2021, 08). Power-law viscoelastic flow of the lower Makran accretionary prism following the 2013 Baluchistan earthquake. Poster Presentation at 2021 SCEC Annual Meeting.

Related Projects & Working Groups
Tectonic Geodesy