Imaging the seismic structure of the western Makran Subduction Zone

• Published in: Geophysical journal international Vol. 242; no. 2
• Main Authors: Mokhtarzadeh, Rahil, Sobouti, Farhad, Priestley, Keith
• Format: Journal Article
• Language: English
• Published: 01.08.2025
• ISSN: 0956-540X; 1365-246X
• DOI: 10.1093/gji/ggaf196

We analyse data from 48 seismic stations located in the western part of the Makran Subduction Zone to gain a detailed knowledge of the crustal and uppermost mantle structure in that region. The Makran is a flat subduction zone with a very thick accretionary wedge. It is a major tsunami hazard of the Indian Ocean but remains one of the world's least studied subduction zones. Its structure and evolution is increasingly becoming a subject of research interest as it can help to better understand the dynamics of flat subduction zones. Our P- and S-wave receiver function analyses reveal that the Arabian oceanic plate is currently dipping north-ward beneath the onshore accretionary wedge at a very low angle of 3°. The depth of the oceanic Moho in the coastal region is ∼30 km due to the presence of ∼22–24 km of sedimentary cover. It increases to ∼60 km beneath the Jazmurian Depression and further deepens to ∼80 km beneath the Bazman and Taftan volcanoes. The change from a relatively flat to a steeper subduction occurs just south of the Qasr-e Qand thrust fault. From the combined results of the receiver function stacking and joint inversion of P-wave receiver functions and Rayleigh wave group dispersion data, we infer that the continental Moho varies within a depth range of 40–56 km, with the shallowest part beneath the Sistan Suture Zone and the deepest beneath the Taftan volcano. Based on shear-wave velocity models, the sedimentary cover thickness in the onshore accretionary wedge varies from Coastal Makran to 34 km in Inner Makran. The lower-than-normal mantle wedge shear-wave velocities suggest that the mantle wedge might have undergone at least 25 per cent serpentinization. From the velocity models we conclude that the crust of the Jazmurian Depression is more likely of continental origin.