Ball-and-socket tectonic rotation during the 2013 Mw7.7 Balochistan earthquake
The September 2013 Mw7.7 Balochistan earthquake ruptured a ∼200-km-long segment of the curved Hoshab fault in southern Pakistan with 10±0.2 m of peak sinistral and ∼1.7±0.8 m of dip slip. This rupture is unusual because the fault dips 60±15° towards the focus of a small circle centered in northwest Pakistan, and, despite a 30° increase in obliquity along strike, the ratios of strike and dip slip remain relatively uniform. Surface displacements and geodetic and teleseismic source inversions quantify a bilateral rupture that propagated rapidly at shallow depths from a transtensional jog near the northern end of the rupture. Static friction prior to rupture was unusually weak (μ<0.05), and friction may have approached zero during dynamic rupture. Here we show that the inward-dipping Hoshab fault defines the northern rim of a structural unit in southeast Makran that rotates – akin to a 2-D ball-and-socket joint – counter-clockwise in response to India's penetration into the Eurasian plate. This rotation accounts for complexity in the Chaman fault system and, in principle, reduces seismic potential near Karachi; nonetheless, these findings highlight deficiencies in strong ground motion equations and tectonic models that invoke Anderson–Byerlee faulting predictions.
Citation Information
Publication Year | 2014 |
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Title | Ball-and-socket tectonic rotation during the 2013 Mw7.7 Balochistan earthquake |
DOI | 10.1016/j.epsl.2014.07.001 |
Authors | William D. Barnhart, Gavin P. Hayes, Richard W. Briggs, Ryan D. Gold, R. Bilham |
Publication Type | Article |
Publication Subtype | Journal Article |
Series Title | Earth and Planetary Science Letters |
Index ID | 70114012 |
Record Source | USGS Publications Warehouse |
USGS Organization | Geologic Hazards Science Center |