Tectonics of the Central Zagros (Iran) deduced from microearthquake seismicity

Abstract

S U M M A R YMicroearthquakes in Central Zagros, recorded for 7 weeks in 1997, lie in a ∼6-8 km zone that is likely located beneath 11 km of sediments. They are not located on an active décollement between the sediments and the crystalline crust, but rather define a pattern of NNW-SSE trending lineaments parallel to the fold axes observed at the surface. The spacing between the seismic lineaments is ∼15-20 km and therefore different from that between the folds (∼10-15 km), which suggests that there is not a simple relationship between the two. Focal mechanisms and precise relative locations are consistent with NW-SE striking reverse faulting connected by NNW-SSE striking right lateral strike-slip faults. The dip of the reverse faults is not certain but is likely NE for the northernmost faults. The strain pattern deduced from the P-axes is remarkably similar to the shortening deduced from GPS-based geodesy suggesting that microearthquakes are the response of the prefractured brittle crust to strain rather than localized on single active faults.

Crustal-scale cross-sections across the NW Zagros belt: implications for the Arabian margin reconstruction

“…These folds display a variety of geometries and sizes, which depend on the distribution of the different detachment levels existing across the sedimentary succession. Similarly to other regions of the Zagros, the present-day seismicity (Berberian, 1995;Engdahl et al 2006;Tatar, Hatzfeld & Ghafori-Ashtiany, 2004) and topography strongly point to the involvement of the whole crust in the deformation of the Pusht-e Kuh arc (e.g. Falcon, 1961;Emami et al 2010;Hatzfeld & Molnar, 2010;Leturmy, Molinaro & Frizon de Lamotte, 2010).…”

“…These NE-dipping thrusts may correspond to the inferred thrust faults within the uppermost crystalline basement identified by the clustering of seismic events (e.g. Tatar, Hatzfeld & Ghafori-Ashtiany, 2004;.…”

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

“…The Zagros mountain fold-andthrust belt in southwestern Iran is one of the largest and most active belts on our planet with continuous seismicity. This northwest-southeast-trending belt extends in southwestern Iran within the Alpine-Himalayan orogenic chain, accommodating approximately 10 mm=yr of north-south shortening between Arabia and Eurasia (Nilforoushan et al, 2003;Tatar et al, 2004;Vernant et al, 2004). Earthquakes with moderate magnitudes of 5.5-6 m b are common in the ∼250-350 km wide zone along the Zagros fold-and-thrust belt (Jackson, 1980a;Berberian, 1995).…”

“…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.…”

Structural Study and Analytical Modeling of Mangerak Salt Diapir (South West of Firozabad Fars-Iran)

“…The Rastalghaz right slip fault is with trending NS that the fault caused the displacement and elongation of at least 10 kilometers around the folds of the region. During the fault, which is composed of at least 6 fault segments, five large salt domes are exposed [20]. South-piece Bas fault by turning to the East Side, creates Sorme thrusting.…”