Iranian Journal of Geophysics

Iranian Journal of Geophysics

Velocity structure of the Iranian Makran subduction zone

Document Type : Research Article

Authors
Ali Mehrdar 1
Khalil Motaghi 2
Abdolreza Ghods 3
Esmail Shabnian 2
1 Ph.D. Student, Department of Earth Sciences, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan, Iran
2 Associate Professor, Department of Earth Sciences, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan, Iran
3 Professor, Department of Earth Sciences, Institute for Advanced Studies in Basic Sciences (IASBS), Zanjan, Iran
10.30499/ijg.2024.464869.1610
Abstract
The Makran subduction zone constitutes a singular component of the Alpine-Himalayan orogenic belt and is located in southeastern Iran and southwestern Pakistan. The Neo-Tethys Ocean's final vestiges are being subducted beneath the Eurasian plate. This study examines how the accretionary prism crust of the Makran subduction zone connects to the Zagros collision zone through the Zendan-Minab-Palami (ZMP) fault system, the thickness of sedimentary cover both along and perpendicular to the collision direction in the Makran accretionary prism in Iran, and the sedimentary changes in the fore-arc Jaz Murian Depression (JMD). It raises questions about the existence of a homogeneous and uniform sedimentary cover in the Jaz Murian depression, considering its classification as a fore-arc basin.
   This study employed ambient noise and regional earthquakes to construct a high-resolution three-dimensional shear wave velocity model for the Iranian Makran region. The Rayleigh wave group velocity dispersion data in the period range of 5 to 50 seconds were obtained through the correlation of continuous vertical-component seismic recordings from broadband stations. The collection of waveforms was conducted using a combination of permanent and temporary seismographs positioned across the Iranian Makran subduction zone. In total, 25 permanent stations were utilized, sourced from the International Institute of Earthquake Engineering and Seismology (IIEES)’s seismic broadband stations, the Iranian Seismological Centre (IRSC), and the Oman Seismological Network (OSN). Additionally, 40 temporary stations, installed by the Institute for Advanced Studies in Basic Sciences (IASBS) between 2016 and 2020, extended coverage to southeastern Iran.
   The three-dimensional shear wave velocity model unveils a remarkably gentle northward-dipping oceanic slab, approximately inclined at 4 degrees, beneath the onshore section of the Makran accretionary wedge. Subsequently, it descends south of Jaz Murian, leading to the subduction of the oceanic lithosphere to depths surpassing 60 kilometers. Also, our results reveal the presence of a transitional zone between the western Makran and the Zagros regions, evident in both surface and deeper geological structures. The transitional lithosphere exhibits a lower shear wave velocity than the oceanic lithosphere and contains a thick sedimentary basin. The typical oceanic lithosphere begins east of the transitional lithosphere. Notably, significant thinning of the sedimentary cover is observed east of 58 degrees longitude within the coastal Makran tectono-stratigraphic unit. The structural trend closely parallels the pattern observed in analogous ophiolites onshore and offshore of Oman. East of the Jaz Murian depression, the maximum thickness of the sedimentary cover reaches 20 kilometers, gradually diminishing towards the western extent of the basin.
Keywords
Makran subduction zone
ambient noise
accretionary wedge
shear wave velocity
transition zone

Subjects

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Iranian Journal of Geophysics
Volume 19, Issue 2
May and June 2025
Pages 63-79