Surface Waveform Tomography Across the Arabian-Eurasian Plate Boundary, Zagros Belt

摘要

Compared with other more evolved plate boundaries, little is known about the deep lithospheric structure of Zagros belt, such as fate of subducted Neo-Tethy s plate and existence of deeply earthquakes. We use the Partitioned Waveform Inversion method to image upper mantle S velocity structure and Moho depth variations across Zagros collisional zone. The resulting Moho depth along the profile shows the average Moho depth value of order of 40-45km for most parts of profile with abrupt crustal thickening in middle of the profile of about 65km. As expected, the derived models show that relatively old and cold Arabian Shield has higher velocity at depth than the younger lithosphere farther north in Central-Iran. A sharp and steep subcrustal boundary is found roughly coincident with the surficial expression of Main Zagros There is a pronounce low-S-velocity layer at depth range of order of 100-150km over whole profile. A high-velocity anomaly, possibly representing a fragment of subducted lithosphere, has been imaged beneath Central Iran at a depth between 350 and 600 km, which is quite similar to the case of Indo-Asian collision in Qinghai-Tibetan plateau. These observations support the idea that subducted oceanic lithosphere has broken-off under the maximum Moho depth area.