Initial Publication Date: May 6, 2014

Anatomy of the 200 km-long, Left-lateral Surface Rupture from the 24 September 2013 Mw7.7 Balochistan Earthquake, Southern Pakistan

Ryan Gold, U.S. Geological Survey
Nadine Reitman, U.S. Geological Survey
Richard Briggs, U.S. Geological Survey
William Barnhart, U.S. Geological Survey
Gavin Hayes, U.S. Geological Survey

The 24 September 2013 Mw7.7 Balochistan earthquake ruptured a ~200 km-long stretch of the Hoshab fault in southern Pakistan. We mapped the extent of this left-lateral surface rupture using high-resolution (0.5 m) pre- and post-event satellite imagery. The continuous rupture passed through several stepovers ranging in width from 0.5-1.0 km. The width of the surface rupture zone ranges from <5 m to 2 km. We find that peak sinistral displacement values measured on geologic piercing points (offset streams, terrace risers, roads, etc.) approach ~12 m and that displacements are inversely correlated to the width of the surface rupture zone (e.g., largest displacements where the fault zone is narrowest). We also analyzed pre-event imagery spanning the Hoshab fault and find evidence for previous strike-slip faulting at the SW and NE extent of the rupture, though evidence is lacking for repeated, frequent, and large strike-slip events on this fault system. Through ongoing analysis of pre- and post-event imagery, we plan to assess the relative percentages of deformation that occurred on-fault as opposed to off-fault. These results will have implications for geologic fault slip-rate studies, paleoseismic studies that estimate earthquake magnitudes from geomorphic offsets, and comparisons of geodetic and geologic slip-rate data.