Tectonic setting of the 2013 May 11 Mw 6.1 Goharan earthquake in western Makran

The Minab–Zendan–Palami (MZP) fault system separates the Makran accretionary wedge in the east from the Zagros fold and thrust belt in the west. The Goharan earthquake of May 21, 2012, with a moment magnitude of 6.1, affected the western part of the Makran accretionary wedge and is located outside of the tectonic domain affected by the MZP. This earthquake was associated with a left-lateral strike-slip surface rupture in the east-west direction. The continental nature of this event is apparently inconsistent with its tectonic setting in the western part of the accretionary wedge of the Makran active subduction. In fact, the causal fault is sub-parallel to the Makran accretionary front and affects an apparently rootless accretionary wedge in which, moderate to large shallow earthquakes are not expected. This study presents new structural geology and active tectonic observations on the area affected by the Goharan earthquake and neighboring regions tectonically related to the earthquake in order to find a seismotectonic explanation for the occurrence of the earthquake. The remote sensing analysis of high-resolution satellite images (Bing satellite image of 0.6 m resampled pixel size in SAS.Planet) and combination of results with available geological and seismological information reveal that active deformation is mainly accommodated by a series of sinistral faults oriented ENE, which are in close structural and kinematic interaction with dextral faults oriented almost N-S. These conjugate fault networks intersect pre-Quaternary geological structures and are independent of structural processes that directly affect both the MZP and the Makran subduction zone. ENE-trending sinistral faults are accompanied by steep structural steps in the North Makran thrust boundaries and correspond to places where abrupt changes in the width of the Inner Makran occur. Our observations imply that (1) west of longitude 61°E, the sinistral faults have been important crustal structures since the initial stage of the Makran wedge formation, (2) interacting with the dextral conjugate series, these Quaternary structures have taken up part of the active NNE-SSW shortening between the Arabian platform and Lut block, without the need for main folding processes and thrust faulting. Those also transfer part of the deformation to the north, and (3) the presence of the sinistral strike-slip faults in this part of the Makran wedge is not accidental; these structures define distinct seismotectonic zones which may host moderate to large continental earthquakes, with a great impact on seismic hazard. This study reveals that structural interactions in complex tectonic settings can produce deformation patterns seemingly inconsistent with our classical understanding of the region's geology.