The diffuse transition between the Zagros continental collision and the Makran oceanic subduction (Iran): microearthquake seismicity and crustal structure

Abstract

International audienceThe nature of the transition between the Zagros intra-continental collision and the Makran oceanic subduction is a matter of debate: either a major fault cutting the whole lithosphere or a more progressive transition associated with a shallow gently dipping fault restricted to the crust. Microearthquake seismicity located around the transition between the transition zone is restricted to the west of the Jaz-Murian depression and the Jiroft fault. No shallow micro-earthquakes seem to be related to the NNW–SSE trending Zendan–Minab–Palami active fault system. Most of the shallow seismicity is related either to the Zagros mountain belt, located in the west, or to the NS trending Sabzevaran–Jiroft fault system, located in the north. The depth of microearthquakes increases northeastwards to an unusually deep value (for the Zagros) of 40 km. Two dominant types of focal mechanisms are observed in this region: low-angle thrust faulting, mostly restricted to the lower crust, and strike-slip at shallow depths, both consistent with NS shortening. The 3-D inversion of P traveltimes suggests a high-velocity body dipping northeastwards to a depth of 25 km. This high-velocity body, probably related to the lower crust, is associated with the deepest earthquakes showing reverse faulting. We propose that the transition between the Zagros collision and the Makran subduction is not a sharp lithospheric-scale transform fault associated with the Zendan–Minab–Palami fault system. Instead it is a progressive transition located in the lower crust. The oblique collision results in partial partitioning between strike-slip and shortening components within the shallow brittle crust because of the weakness of the pre-existing Zendan–Minab–Palami faults

The transition between Makran subduction and the Zagros collision: recent advances in its structure and active deformation

“…Finally, Yamini-Fard et al (2007) computed a local 3D crustal velocity structure and relocated simultaneously the local earthquakes inverting the travel times of local seismicity (Yamini-Fard et al, 2007). The resulting velocity structure suggests a high velocity body dipping northeastward (Figure 8).…”

“…Regard et al(2004) Figure 5) from Molinaro et al (2004). C-C' is the local tomography cross-section (Figure 8), from Yamini-Fard et al (2007).…”

“…3.3.1 Seismotectonics Yamini-Fard et al (2007) installed a dense seismological mobile network of 24 stations for 8 weeks in 1999, in the area of Bandar Abbas, to locate precisely the microseismicity of the area and calculate focal mechanisms ( Figure 6). In addition, they realised a tomographic traverse, with 25 stations from Hadjiabad to Minab and the Makran ranges ( Figure 7).…”

The 18 August 2014 Mw 6.2 Mormori, Iran, Earthquake: A Thin-Skinned Faulting in the Zagros Mountain Inferred from InSAR Measurements

“…Much work has been done in the past to improve our understanding of the shortening mechanism in the Zagros (Koyi et al, 2000;Tatar et al, 2004;Yamini-Fard et al, 2007;Authemayou et al, 2009;Oveisi et al, 2009). Both thickskinned deformation (Jackson, 1980b;Berberian, 1995) and thin-skinned deformation (Hessami et al, 2006;Walpersdorf et al, 2006) models have been proposed for geodynamic evolution of Zagros orogeny; in the former model, the shortening is accommodated by reverse basement faulting that is separated from shallow sedimentary rocks by the infra-Cambrian Hormuz salt sequence, and, in the latter model, active folding of the shallow sediments is the main deformation mechanism.…”

Probabilistic seismic hazard maps for the sultanate of Oman

“…Historical (Ambraseys and Melville 1982;Musson 2009) and instrumental seismicity (e.g. Gholamzadeh et al 2009), as well as microseismic activity (Yamini-Fard et al 2007), appear to be essentially limited to the Zagros domain. Seismicity appears to neither be associated with the Minab-Zendan nor Jiroft-Sabzevaran faults, suggesting that the transition between the Zagros collision and the Makran subduction is not a sharp transform fault.…”