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 wedge, and a volcanic arc not parallel to the E-W trend of the Makran accretionary prism. To investigate the internal structure of the onshore accretionary wedge, the trend of the buried trench, and the crustal nature of fore-arc Jaz Murian Depression, 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. Our 3D shear-wave velocity model clearly shows that the onshore accretionary prism consists of two southern low and northern high velocity zones with an average sedimentary cover 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 scraped from the subducting oceanic slab. The 3D model indicates a continental crust of ~40 km with a thick sedimentary cover of ~20 km for the eastern part of Jaz Murian Depression. The presence of a NE-SE 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 buried trench. This implies that the observed NE-SE trending volcanic arc might be related to the geometry of the buried trench and not the eastward reduction of the subduction angle.