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 a 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 buried trench 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 scraped from the subducting oceanic slab. The velocity 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-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 buried trench. This implies that the observed NE-SW trending volcanic arc might be related to the geometry of the buried trench and not the eastward reduction of the subduction angle.

Methods
The dataset is related to Makran IASBS/CAMB temporary seismic network. The network worked during June 2016 to Sep 2020. The network was installed by Institute for Advanced studies in Basic Sciences, Zanjan, Iran (iasbs.ac.ir). The data comprises of the following items,

1) Ambient noise green functions between all possible stations used in the study

2) Initial and final 3D shear-velocity model

3) Adjoint sources for the final iteration