Crustal and uppermost mantle structure of the Iranian Makran subduction zone from ambient noise and earthquake surface wave tomography

SUMMARY The Makran subduction zone is a distinctive segment within the Alpine–Himalayan system, where one of the final remnants of the once-expansive Neo-Tethys Ocean is being subducted beneath the Eurasian Plate. Limited seismic data has left several questions unanswered about the structure of the subducting oceanic lithosphere, the transition from the wide and thick Makran accretionary prism to the Zagros Collision Zone, variations in sedimentary cover thickness along and perpendicular to the accretionary prism, and fluctuations in the thickness of sedimentary cover within the fore-arc Jaz Murian Depression (JMD). In this study, we utilize ambient-noise and earthquake surface wave tomography within a period range of 5–50 s to construct a high-resolution 3-D shear-wave velocity model down to a depth of 60 km for the Iranian Makran and northern Oman. Using a new data set from 65 seismic stations located in southeastern Iran and northern Oman, our analysis reveals a sharp velocity contrast within the oceanic lithosphere of the Gulf of Oman, just north of Muscat, with abnormally low-velocity oceanic lithosphere extending westward from this contrast, revealing subduction of a segmented oceanic lithosphere beneath the Makran. Our study finds no lithospheric-scale seismic velocity contrast along the Zendan-Minab-Palami fault, as usually thought as a transition boundary between the Zagros and Makran. Our velocity model shows that the wide accretionary prism of western Makran consists of two zones: a southern low-velocity zone associated with younger sediments and a northern high-velocity zone corresponding to older sediments. A considerable thinning of the sedimentary cover is observed east of longitude 59°E within the coastal Makran tectono-stratigraphic unit, aligning with the structural trend of the Pan-African Semail Gap Fault observed both onshore and offshore Oman. Additionally, a thick sedimentary basin is located beneath the eastern section of the JMD, with the thickness decreasing towards the west.