High‐Resolution Local Earthquake Tomography Beneath the Zagros Simply Folded Belt (SFB): Implications for an Inhomogeneous Low‐Velocity Layer and Diapirism in the Upper Crust

• Published in: Earth and space science (Hoboken, N.J.) N.J.), 2023-08, Vol.10 (8), p.n/a
• Main Authors: Kianimehr, H., Kissling, E., Yaminifard, F., Tatar, M.
• Format: Article
• Language: English
• Subjects: Aftershocks; Earthquakes; Fault lines; Geology; Global positioning systems; GPS; low velocity anomalies; Mountains; Salts; Sedimentation & deposition; Sediments; Seismic activity; seismic tomography; the Hormuz salt layer; the SFB; Tomography; Velocity
• ISSN: 2333-5084; 2333-5084
• DOI: 10.1029/2022EA002691

Hormuz salt formation is considered the origin of the evaporated salt deposits in the Zagros and its ductile behavior has been known as the reason for the inhomogeneous deformation in the Zagros. However, our knowledge about this formation has been limited to the salt domes on the surface. In our study, local earthquakes recorded by a temporary dense seismological network of 17 stations, deployed in the southern margin of the Zagros Simply Folded Belt (SFB) in southwestern Iran, have been used for seismic imaging. The high‐resolution earthquake local tomography revealed the first geophysical evidence about the Hormuz salt layer and its extension at depth. There is an uneven layer located at a depth of 8–12 km as the origin of extruded salt in this region through a shear fault zone and the production of the Dashti Salt Dome at the Kuh‐e‐Namak Mountain. Based on the obtained results, this layer is characterized by low seismic velocity volumes with significant Vp/Vs ratio variations. The seismic image is also consistent with a major NW‐trending NE‐dipping reverse fault, probably responsible for the 9 April 2013 Kaki earthquake. At depth of around 4 km, smaller scale high velocity anomalies, characterized by a high Vp/Vs ratio, may be related to the fluid saturated sediments in the uppermost sedimentary layer. There are many diapirs in the Simply Folded Belt, which are corresponded to a known formation, Hormuz. Most of our knowledge about this structure is restricted to the achieved information of studying salt diapirs; however, there is no reliable investigation about the depth extension of that. In this study, using a high‐resolution earthquake data set, for the first time we modeled tomographic images in order to present a new insight into the geological structures in this part of the Zagros mountain range, southwestern of Iran. The obtained results imply an irregular extension of low‐velocity volumes that reach to the surface through likely faults as salt domes. Moreover, these results indicate the Kaki earthquake causative fault with a major NW‐trending with NE dipping, reverse mechanism. A dense network of 17 seismic stations as deployed around the Mw 6.2 Kaki earthquake epicenter The first high‐resolution seismic tomography in the Simply Folded Belt (SFB), suggests the low velocity zones at depth reaching the well‐known salt domes The weak mechanical materials in the upper crust have a significant effect on the aseismic deformation and rupture propagati