The 2005 Qeshm Island earthquake (Iran)-a link between buried reverse faulting and surface folding in the Zagros Simply Folded Belt?

Abstract

Qeshm Island earthquake (M w 6.0) provides an excellent opportunity to study coseismic deformation in the Zagros Simply Folded Belt with Synthetic Aperture Radar interferometry (InSAR). Typical of reverse faulting in the Zagros, slip in the Qeshm Island earthquake did not rupture the surface. However, ascending and descending track interferograms spanning the earthquake both show an elliptical pattern of surface deformation in the central part of the island. We invert the interferometric data to attain a set of source parameters; these show ∼1 m slip on a steep (∼50 • ), north-dipping reverse fault, extending from a maximum depth of ∼8 up to ∼4 km below the surface. Limited aeromagnetic data suggests the fault ruptured the sedimentary cover; whether its deepest parts also affected the crystalline basement is not clear. Source parameters from seismic body wave modelling agree with those from the interferometric modelling. Using the InSAR-derived model, we produce a map of coseismic vertical displacements, with which we compare the surface structure of the island. Coseismic uplift is centred on the eastern end of a major anticline, which trends E-W, parallel with the fault. The long-term growth of this fold may be controlled primarily by repeated earthquakes on this fault. However, the uplifted region extends to parts of other nearby folds, whose long-term growth must have other controls; moreover, a region of coseismic subsidence lies very close to a part of the Qeshm island coastline that displays raised beaches, evidence of Quaternary uplift. Therefore the link between reverse faulting and surface folding is not wholly evident from this earthquake alone. The local structure is complicated by orthogonal fold axes; it may take a large earthquake in a simpler structural setting within the Zagros to establish convincingly whether a one-to-one correlation between faulting and folding exists.

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

“…Similar observations of surface shortening in the overlying sediments have been made for the recent earthquakes in the Zagros, including the 27 November 2005 (Nissen et al, 2007;Amighpey et al, 2014) and the 10 September 2008 Faegh-Lashgary et al, 2012) earthquakes in Qeshm and the 25 March 2006 Fin earthquake (Roustaei et al, 2010). The previously unmapped blind-thrust fault that was activated in the 2014 Mormori event dies out upward into the Gachsaran salt (Fig.…”

“…The focal solutions reported by the Global CMT catalog and U.S Geological Survey/National Earthquake Information Center (USGS/NEIC) provide similar mechanisms for NP1 and NP2 (Table 1). Previous studies suggest the existence of both north-dipping and south-dipping active thrust in the Zagros (Nissen et al, 2007Roustaei et al, 2010). Our fault model for the 2014 Mormori earthquake strongly favors a northeast-dipping NP2 plane in seismic observations.…”

Earth surface deformation analysis of 2005 Qeshm earthquake based on three-dimensional displacement field derived from radar imagery measurements

“…A comparison between the obtained interpretations with other studies carried out on Qeshm earthquake, manifested a good agreement between our proposed causative faults and seismicity studies carried out by Gholamzadeh et al (2007). However, the obtained results demonstrated a low correlation with the InSAR-derived model achieved by Nissen et al (2007).…”

“…Toward the end of the decade, InSAR has been increasingly used for measuring the deformation of the earth's surface caused by earthquakes (Peltzer and Rosen, 1995;Stramondo et al, 1999;Fialko et al, 2001;Funning et al, 2005;Nissen et al, 2007). This new geodetic technique calculates the interference patterns caused by the difference in phase between two images acquired by synthetic aperture radar at two distinct times.…”

Chapter 2 Active tectonics of Myanmar and the Andaman Sea

“…Uplift patterns derived from InSAR studies indicate that there is no simple direct relationship between longterm anticlinal uplift and the pattern of uplift associated with individual earthquakes (e.g. Nissen et al 2007Nissen et al , 2010Roustaei et al 2010). Nissen et al (2011) suggest that the presence of weak layers within the sedimentary succession plays an important role in limiting the size of earthquake rupture.…”