3D Shear-Wave Velocity Model of Central Makran Using Ambient-Noise Adjoint Tomography

The Makran subduction zone is unique in its wide onshore thick accretionary prism, and volcanic arc not parallel to the E-W trend of the Makran accretionary prism. To investigate the internal structure of the accretionary prism, the crustal nature of Jaz Murian Depression, and the trend of the subducting plate hinge, we have calculated a 3D shear-wave velocity model for a region around the border between eastern and western Makran using ambient-noise adjoint tomography and data from IASBS/CAM Makran temporary seismic network. In close agreement with previous works, our velocity model shows that the onshore accretionary prism consists of a low-velocity zone in the south and a high-velocity zone in the north with an average thickness of accreted sediments of 22 and 30 km, respectively. The young age of the surface rocks of the high-velocity part of the prism suggests the presence of a significant volume of igneous rocks and metamorphosed sedimentary rocks. The velocity model indicates a continental crust of similar to 40 km with a thick sedimentary cover of similar to 20 km for the eastern part of Jaz Murian Depression. The presence of a NE-SW trending low-velocity region at a depth interval of 40-60 km subparallel with the trend of the volcanic arc, intermediate-depth earthquakes, and geometry of the overriding plate might be related to the trend of the subducting plate hinge. This implies that the observed NE-SW trending volcanic arc might be related to the geometry of the subducting plate hinge and not the eastward reduction of the subduction angle.