Surface slip and off‐fault deformation patterns in the 2013 M_W 7.7 Balochistan, Pakistan earthquake: Implications for controls on the distribution of near‐surface coseismic slip

Abstract

Comparison of 398 fault offsets measured by visual analysis of WorldView high-resolution satellite imagery with deformation maps produced by COSI-Corr subpixel image correlation of Landsat-8 and SPOT5 imagery reveals significant complexity and distributed deformation along the 2013 M w 7.7 Balochistan, Pakistan earthquake. Average slip along the main trace of the fault was 4.2 m, with local maximum offsets up to 11.4 m. Comparison of slip measured from offset geomorphic features, which record localized slip along the main strand of the fault, to the total displacement across the entire width of the surface deformation zone from COSI-Corr reveals 45% off-fault deformation. While previous studies have shown that the structural maturity of the fault exerts a primary control on the total percentage of off-fault surface deformation, large along-strike variations in the percentage of strain localization observed in the 2013 rupture imply the influence of important secondary controls. One such possible secondary control is the type of near-surface material through which the rupture propagated. We therefore compared the percentage off-fault deformation to the type of material (bedrock, old alluvium, and young alluvium) at the surface and the distance of the fault to the nearest bedrock outcrop (a proxy for sediment thickness along this hybrid strike slip/reverse slip fault). We find significantly more off-fault deformation in younger and/or thicker sediments. Accounting for and predicting such off-fault deformation patterns has important implications for the interpretation of geologic slip rates, especially for their use in probabilistic seismic hazard assessments, the behavior of near-surface materials during coseismic deformation, and the future development of microzonation protocols for the built environment.

Landers 1992 "reloaded": Integrative dynamic earthquake rupture modeling

“…While the major features of the modeled off-fault deformation pattern are related to the changing fault orientation, the existing discrepancies might be related to missing heterogeneous structure along the fault segments. Off-fault deformation correlates with the near-surface lithology that either promote or prevent off-fault damage [Zinke et al;Milliner et al, 2016]. …”

Geological structures control on earthquake ruptures: The Mw7.7, 2013, Balochistan earthquake, Pakistan

“…In few cases, combining such measurements with interferometric synthetic aperture radar allowed accessing the full 3-D surface deformation field and slip at depth [Fialko et al, 2001;Grandin et al, 2009;Vallage et al, 2015]. The 2013 M w 7.7 Balochistan earthquake occurred on the eastern part of the Makran accretionary wedge, Pakistan ( Figure 1a) [Avouac et al, 2014;Barnhart et al, 2014Barnhart et al, , 2015Jolivet et al, 2014;Zinke et al, 2014]. Those variations are related to surficial geometrical complexities, evidencing at-depth fault segmentation at the scale of 10 to 20 km [Wei et al, 2011].…”

“…Large-scale kinks and jogs have seemed to control part of the rupture Zinke et al, 2014]. Large-scale kinks and jogs have seemed to control part of the rupture Zinke et al, 2014].…”

An Investigation of 2013 M_w 7.7 Awaran Earthquake, Pakistan

“…Hoshab fault is located in Makran accretionary complex. 3 cm/yr of convergence between Arabia and Eurasia is being accommodated by Makran convergence zone [15]. The area is characterized by Panjgur, Naib Rub and Hoshab fault system (PHNFS) which are east west oriented reverse faults [13].…”

“…Studies by Zhou et al 2015 [12] suggests that the failure is not solely constrained to Hoshab fault but occurs in a distributed fashion thus providing an explanation to lack of seismicity previously and also to long repeat times. Younger and thicker sediments have more off-fault deformation [15]. Both reverse slip and strike slip deformation in rupture area was depicted by Quaternary geomorphic indicators.…”