Subduction tractions and vertical axis rotations in the Zagros–Makran transition zone, SE Iran: the 2013 May 11M_w6.1 Minab earthquake

Abstract

S U M M A R YThe source parameters and slip distribution of the 2013 May 11 M w 6.1 Minab earthquake are studied using seismology, geodesy and field observations. We observe left-lateral strike-slip motion on a fault striking ENE-WSW; approximately perpendicular to previously studied faults in the Minab-Zendan-Palami fault zone. The fault that ruptured in 2013 is one of a series of ∼E-W striking left-lateral faults visible in the geology and geomorphology. These accommodate a velocity field equivalent to right-lateral shear on ∼N-S striking planes by clockwise rotations about vertical axes. The presence of these faults can reconcile differences in estimates of fault slip rates in the western Makran from GPS and Quaternary dating. The longitudinal range of shear in the western Makran is likely to be controlled by the distance over which the underthrusting Arabian lithosphere deepens in the transition from continentcontinent collision in the Zagros to oceanic subduction in the Makran.Key words: Earthquake source observations; Continental neotectonics; Asia. I N T RO D U C T I O NThe 2013 May 11 M w 6.1 Minab earthquake occurred in the sparsely populated desert to the east of the Strait of Hormuz, in SE Iran (Fig. 1). The earthquake occurred in the western part of the Makran subduction zone, where Arabian oceanic lithosphere is thrust beneath southern Iran and Pakistan. To the west, this oceanic subduction transitions into continent-continent collision in the Zagros mountains of Iran. The Minab earthquake presents an opportunity to address a number of open questions, such as those raised by the M w 7.7 Balochistan earthquake in 2013; a strike-slip event that ruptured a curved fault at the eastern end of the Makran subduction zone (Avouac et al. 2014;Jolivet et al. 2014). That event highlighted that the onshore part of the accretionary wedge built above the subduction interface can be seismically active and characterized by strike-slip faulting. We examine the 2013 Minab event to better understand the deformation of the accretionary wedge in the Zagros-Makran transition zone. This earthquake is also important from the perspective of understanding the regional tectonics and distribution of strain in the western Makran, which give insights into both earthquake hazard and the factors controlling the distribution and style of faulting in the continents. This paper addresses these issues by studying the 2013 Minab earthquake using a combination of seismology, satellite geodesy and field observations. We then consider the implications of our results for the driving forces and distribution of faulting in the region. B O DY WAV E F O R M M O D E L L I N GTeleseismic P and SH waveforms in the epicentral distance range 30-80• were extracted from the IRIS DMC. The seismograms were deconvolved from their instrument responses and reconvolved with the response of a World-Wide Standardised Seismographic Network Long Period (15-100) seismometer. In this period range, a moderate-size earthquake can be approximated as a point source....

Megathrust and accretionary wedge properties and behaviour in the Makran subduction zone

“…McKenzie and Jackson, 1986). Such vertical-axis rotations accommodate some of the right-lateral shear at the northern end of the SSZ, for example on the Dasht-e-Bayaz fault , and have been reported at the western margin of the Makran (Penney et al, 2015).…”

“…Where available, we use published earthquake depths and mechanisms from this technique (Laane and Chen, 1989;Byrne et al, 1992;Baker, 1993;Berberian et al, 2000;Maggi et al, 2000;Berberian et al, 2001;Jackson et al, 2006;Talebian et al, 2006;Engdahl et al, 2006;Nissen et al, 2010Nissen et al, , 2011Walker et al, 2013;Barnhart et al, 2014b;Jolivet et al, 2014;Penney et al, 2015). In addition, we have used teleseismic P and SH bodywaveform modelling to determine the depths and focal mechanisms of 7 earthquakes for which solutions have not previously been published.…”

“…A final possibility is that the right-lateral motion of the SSZ is transferred onto the faults of the Minab-Zendan-Palami (MZP) fault zone ( Figure 1) and nearby strike-slip faults (Penney et al, 2015), which, combined, accommodate ∼17 mm/yr of right-lateral shear (Peyret et al, 2009). Geometrically, this scenario requires the Jaz Murian depression to be bounded by normal faults (Figure 5c).…”

“…This is accommodated by both the N-S striking faults of the Minab-Zendan-Palami fault zone (e.g. Figure 1) and left-lateral E-W striking faults to the east (Penney et al, 2015), which rotate clockwise about vertical axes. The total motion from shortening in the Zagros, right-lateral faults to the north in the Sabzevaran-Jiroft fault system, and the faults of the SSZ is ∼18 mm/yr, so the rate of right-lateral shear in the western Makran is sufficient to take up that motion.…”

Seismogenic faulting of the sedimentary sequence and laterally variable material properties in the Zagros Mountains (Iran) revealed by the August 2014 Murmuri (E. Dehloran) earthquake sequence

“…This feature is often seen for events in the Zagros Mountains and Makran (e.g. Lohman & Simons 2005;Nissen et al 2010;Roustaei et al 2010;Penney et al 2015), and is usually interpreted to represent post-seismic afterslip contributing towards the geodetically measured moment, or systematic errors in the velocity models used. In addition, because the available InSAR data has only one look-angle for the Murmuri events, it should also be noted that the rake in the geodetic inversions is relatively poorly constrained (and reliant on the imposed seismological limits), so the moment in the InSAR inversions will be subject to a trade-off between the rake and the amount of fault slip.…”