Seismic structure of the western Makran Subduction Zone from the joint inversion of receiver functions and surface wave dispersion data

We analyze data from a temporary seismic network located in southeastern Iran to gain a detailed knowledge of the crustal and uppermost mantle structure in the western Makran Subduction Zone. Our P- and S-wave receiver function analyses reveal that the the Arabian Oceanic Plate is currently dipping north-ward beneath the onshore accretionary wedge at a very low angle of ۳∘. The depth of the oceanic Moho is ~۳۰ km in the coastal region, increasing to ~۶۰ km beneath the Jazmurian Depression and further deepening to ~۸۰ km beneath the Bazman and Taftan volcanos. The change from a relatively flat to a steeper subducting oceanic plate occurs just south of the Qasr-e Qand thrust fault. The S-wave receiver function images clearly indicate the lithosphere-asthenosphere boundary beneath the Arabian Plate, ranging from a depth of ~۹۰ km in the coastal region to ~۱۵۰ km in the northern margin of the Jazmurian Depression. We infer that the continental Moho varies within a depth range of ۴۰ to ۵۶ km, with the shallowest part beneath the Sistan Suture Zone and the deepest beneath the Taftan volcano. We also determined that the sedimentary cover thickness in the on-shore accretionary wedge varies from ۲۲ km in Coastal Makran to ۳۴ km in Inner Makran. The lower-than-normal mantle wedge shear-wave velocities suggest that the mantle wedge might have undergone at least ۲۵% serpentinization. Furthermore, from the shear velocity models we conclude that the crust of the Jazmurian Depression is more likely of continental origin.

کلیدواژه ها:

Subduction Zone ، Moho ، Receiver function ، dispersion Curve ، Makran