New Constraints for the OnâShore Makran Subduction Zone Crustal Structure
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jats:titleAbstract</jats:title>jats:pThe Makran Subduction Zone is the primary seismic/tsunami hazard of the northwestern Indian Ocean, but little is known of its onâshore seismic structure. We derived a shear wave velocity model extending to <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/jgrb55383-math-0001.png" xlink:title="urn:x-wiley:21699313:media:jgrb55383:jgrb55383-math-0001" />100 km depth beneath a âź400 kmâlong seismic profile oriented parallel to the convergence vector of the Arabian Sea Plate. Receiver function/surface wave analysis shows that the average structure in the coastal region comprises a âź22â28 kmâthick low wavespeed sedimentary cover and a 6â8 kmâthick gradient zone overlying <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/jgrb55383-math-0002.png" xlink:title="urn:x-wiley:21699313:media:jgrb55383:jgrb55383-math-0002" />100 kmâthick high wavespeed upper mantle. The oceanâbasement interface dips gently northward, remaining a positive impedance contrast to âź50 km depth at âź250 km north of the coast where it disappears as the basaltic/gabbroic oceanic crust has probably transformed to eclogite. Further north, a weak arrival at âź5 s in the receiver functions appears, grading northward into the Moho arrival of the continental Iranian Plateau. This disruption in the seismic signature of the Moho occurs in the forearc region where the dip of the subducting oceanic plate steepens. The southern Iranian Plateau's continental crust has an average jats:italicV</jats:italic>jats:subjats:italics</jats:italic></jats:sub> of 3.55 Âą 0.05 km sjats:supâ1</jats:sup>, an almost flat Moho 40â45 km deep, and a subâMoho mantle jats:italicV</jats:italic>jats:subjats:italics</jats:italic></jats:sub> of 3.75 Âą 0.05 km sjats:supâ1</jats:sup> in the 50â80 km depth range. Weak Moho conversions probably result from âź20% serpentinization of peridotite in the mantle wedge. Receiver functions indicate a flat continental Moho â no crustal root beneath the high topography region of the volcanic belt, which therefore must be compensated by low upper mantle densities. The high jats:italicV</jats:italic>jats:subjats:italicp</jats:italic></jats:sub>/jats:italicV</jats:italic>jats:subjats:italics</jats:italic></jats:sub> ratio observed for the mantle wedge suggests âź1%â2% partial melt.</jats:p>
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Funder: Institute for Advanced Studies in Basic Sciences; Id: http://dx.doi.org/10.13039/501100007513
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2169-9356
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Natural Environment Research Council (NERC) (NE/J019895/1)