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

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.ISSN:2333-508

Active faults in the west of the Lut Block (Central Iran)

The western margin of the Lut Block, in southeastern Iran, has experienced many historical and instrumental destructive earthquakes where 13 earthquakes, from 1977 to 2020, totally had surface rupture with a length of roughly 207 km. In this study, we indicated active tectonic evidence of the fundamental faults based on the DEM terrain interpretation, and satellite data analysis with field data. We investigated surface evidence related to the activity of the faults and their depth characteristics. Our results of the geometric-kinematic characteristic of the faults have general applications in describing strike-slip faults, development of releasing, and restraining bends in positive flower structures

Active faults in the west of the Lut Block (Central Iran)

The western margin of the Lut Block, in southeastern Iran, has experienced many historical and instrumental destructive earthquakes where 13 earthquakes, from 1977 to 2020, totally had surface rupture with a length of roughly 207 km. In this study, we indicated active tectonic evidence of the fundamental faults based on the DEM terrain interpretation, and satellite data analysis with field data. We investigated surface evidence related to the activity of the faults and their depth characteristics. Our results of the geometric-kinematic characteristic of the faults have general applications in describing strike-slip faults, development of releasing, and restraining bends in positive flower structures

Active faults in the west of the Lut Block (Central Iran)

The western margin of the Lut Block, in southeastern Iran, has experienced many historical and instrumental destructive earthquakes where 13 earthquakes, from 1977 to 2020, totally had surface rupture with a length of roughly 207 km. In this study, we indicated active tectonic evidence of the fundamental faults based on the DEM terrain interpretation, and satellite data analysis with field data. We investigated surface evidence related to the activity of the faults and their depth characteristics. Our results of the geometric-kinematic characteristic of the faults have general applications in describing strike-slip faults, development of releasing, and restraining bends in positive flower structures

Active faults in the west of the Lut Block (Central Iran)

The western margin of the Lut Block, in southeastern Iran, has experienced many historical and instrumental destructive earthquakes where 13 earthquakes, from 1977 to 2020, totally had surface rupture with a length of roughly 207 km. In this study, we indicated active tectonic evidence of the fundamental faults based on the DEM terrain interpretation, and satellite data analysis with field data. We investigated surface evidence related to the activity of the faults and their depth characteristics. Our results of the geometric-kinematic characteristic of the faults have general applications in describing strike-slip faults, development of releasing, and restraining bends in positive flower structures

Strain rate and stress fields in the West and South Lut block, Iran: Insights from the inversion of focal mechanism and geodetic data

The active tectonic deformation and hazardous earthquakes in the south and west of the Lut block have been investigated for a long time. In this study, we compute the geodetic and seismic strain rates using focal mechanism data from the Harvard CMT catalogue and various other sources including the published GPS velocities. Moreover, we also perform Focal Mechanism Stress Inversion (FMSI) to deduce a stress model for the region. Our study shows an expected correlation between the stress orientations, seismic and geodetic strain rates. Our results show that the south and west of the Lut block is generally exposed as a compressional strike-slip tectonic regime. The tectonic convergence in this area is taken up not only by motions along and across the faults but also by the rotation of those blocks which bounded by these faults. The maximum amount of rotation rate is observed where there are the main right lateral strike slip fault systems such as Sabzevaran, Gowk, Nayband, Bam, Kuhbanan, and Kahurak. The orientation of the mean stress direction, obtained from the FMSI results in the west and south of the Lut block, is approximated ~N19 E. In this area, faults are almost oblique relative to the tectonic motion direction. Moreover, there are right-lateral and left-lateral shears, in addition to the dip movements in different parts of the south and west of the Lut block. Our analyses show three main categories of the stress regimes including strike-slip faulting (43.2%), thrust faulting (38.6%), and unknown or oblique faulting (18.2%). We also calculated seismic and geodetic moment rates for this area, which indicate the seismic moment rate is relatively high between Bam and Shahdad where there are some segments of the Gowk fault

Strain rate and stress fields in the West and South Lut block, Iran: Insights from the inversion of focal mechanism and geodetic data

The active tectonic deformation and hazardous earthquakes in the south and west of the Lut block have been investigated for a long time. In this study, we compute the geodetic and seismic strain rates using focal mechanism data from the Harvard CMT catalogue and various other sources including the published GPS velocities. Moreover, we also perform Focal Mechanism Stress Inversion (FMSI) to deduce a stress model for the region. Our study shows an expected correlation between the stress orientations, seismic and geodetic strain rates. Our results show that the south and west of the Lut block is generally exposed as a compressional strike-slip tectonic regime. The tectonic convergence in this area is taken up not only by motions along and across the faults but also by the rotation of those blocks which bounded by these faults. The maximum amount of rotation rate is observed where there are the main right lateral strike slip fault systems such as Sabzevaran, Gowk, Nayband, Bam, Kuhbanan, and Kahurak. The orientation of the mean stress direction, obtained from the FMSI results in the west and south of the Lut block, is approximated ~N19 E. In this area, faults are almost oblique relative to the tectonic motion direction. Moreover, there are right-lateral and left-lateral shears, in addition to the dip movements in different parts of the south and west of the Lut block. Our analyses show three main categories of the stress regimes including strike-slip faulting (43.2%), thrust faulting (38.6%), and unknown or oblique faulting (18.2%). We also calculated seismic and geodetic moment rates for this area, which indicate the seismic moment rate is relatively high between Bam and Shahdad where there are some segments of the Gowk fault