Megathrust and accretionary wedge properties and behaviour in the Makran subduction zone

• Main Authors: Penney, Camilla, Tavakoli, F, Saadat, A, Nankali, HR, Sedighi, M, Khorrami, F, Sobouti, F, Rafi, Z, Copley, Alexander, Jackson, James, Priestley, Keith
• Format: Text
• Language: English
• Published: Apollo - University of Cambridge Repository 2017
• Subjects: seismic cycle; seismicity and tectonics; rheology and friction of fault zones; subduction zone processes; Asia; Seismological Facilities for the Advancement of Geoscience and EarthScope
• Online Access: https://dx.doi.org/10.17863/cam.10529; https://www.repository.cam.ac.uk/handle/1810/264787

We study the Makran subduction zone, along the southern coasts of Iran and Pakistan, to gain insights into the kinematics and dynamics of accretionary prism deformation. By combining techniques from seismology, geodesy and geomorphology, we are able to put constraints on the shape of the subduction interface and the style of strain across the prism. We also address the long-standing tectonic problem of how the right-lateral shear taken up by strike-slip faulting in the Sistan Suture Zone in eastern Iran is accommodated at the zone’s southern end. We find that the subduction interface in the western Makran may be locked, accumulating elastic strain, and move in megathrust earthquakes. Such earthquakes, and associated tsunamis, present a significant hazard to populations around the Arabian Sea. The time-dependent strain within the accretionary prism, resulting from the megathrust earthquake cycle, may play an important role in the deformation of the Makran region. By considering the kinematics of the 2013 Balochistan and Minab earthquakes, we infer that the local gravitational and far-field compressive forces in the Makran accretionary prism are in balance. This force balance allows us to calculate the mean shear stress and effective coefficient of friction on the Makran megathrust, which we find to be 5–35 MPa and 0.01–0.03, respectively. These values are similar to those found in other subduction zones, showing that the abnormally high sediment thickness in the offshore Makran does not significantly reduce the shear stress on the megathrust. : This work forms part of the NERC- and ESRC-funded project ‘Earthquakes without Frontiers’ and was partially supported by the NERC large grant ‘Looking inside the Continents from Space’. CP is funded by an NERC studentship. The facilities of IRIS Data Services, and specifically the IRIS Data Management Center, were used for access to waveforms, related metadata, and/or derived products used in this study. IRIS Data Services are funded through the Seismological Facilities for the Advancement of Geoscience and EarthScope (SAGE) Proposal of the National Science Foundation under Cooperative Agreement EAR-1261681.