A viscous accretionary prism: InSAR observations following the 2013 Baluchistan, Pakistan earthquake

• Main Author: Peterson, Katherine Elizabeth
• Other Authors: Barnhart, William D.
• Format: Others
• Language: English
• Published: University of Iowa 2018
• Subjects: Accretionary prism; Earthquakes; Geodesy; InSAR; Post-seismic deformation; Geology
• Online Access: https://ir.uiowa.edu/etd/6484; https://ir.uiowa.edu/cgi/viewcontent.cgi?article=7984&context=etd

Geodetic observations are commonly used to make inferences about the rheology of the lower crust and mantle, frictional properties of faults, and the structure of the Earth following an earthquake. On 24 September 2013, an Mw 7.7 earthquake ruptured a 200 km segment of the Hoshab fault in southern Pakistan. The Hoshab fault is located in the Makran accretionary prism, one of the widest emergent accretionary prisms on Earth. Interferometric synthetic aperture radar (InSAR) time series observations beginning 15 months after the 2013 earthquake capture a large displacement transient in the hanging wall of the Hoshab fault. Using simulations of viscoelastic relaxation and inversions for afterslip along five candidate fault geometries, I find that afterslip alone cannot account for the displacement observed in time series. Instead, I find that the observations can be explained by viscoelastic relaxation of a mechanically weak (viscosity on the order of 1017-1018 Pa s), shallow (>6 km) weak layer within the accretionary prism. First order results indicate this weak layer is between 8-12 km thick with a power law (n=3.5) rheology, and that viscoelastic relaxation is accommodated by dislocation creep at low temperatures. The weak nature of the Makran accretionary wedge may be driven by high pore fluid pressure from hydrocarbon development and underplated sediments.