Abstract
The Strait of Hormuz area is a transition zone between the continental collision of the Zagros (west) and the subduction of an oceanic part of the Arabian Plate beneath the Makran wedge (east). Geology and recent GPS measurements indicate that about 15 mm yr−1 of relative motion in N10°E direction is accommodated by two major fault systems: (1) the NNW-trending Minab-Zendan-Palami (MZP) fault system that connects the Main Zagros Thrust (MZT) to the inner Makran thrust system and the Frontal subduction thrust and (2) the N-trending Sabzevaran-Kahnuj-Jiroft (SKJ) fault system that bounds the Jazmurian depression to the west. We use dense GPS measurements along four transects across these fault systems in order to determine the strains spatial distribution. The northern GPS transect confirms the total fault slip rates for both fault systems estimated by the tectonic analyses (about 10 and 7.3 mm yr−1 in N10° direction across the MZP and SKJ fault systems, respectively). For both fault systems, the elastic deformation spreads over shear zones that are several tens of kilometres wide. However, transects located close to latitude 27°N reveal a much narrower shear zone (∼10 km) for the MZP fault system. Moreover, we confirm that most of the present-day strain is transferred towards the frontal subduction thrust rather than towards the inner Makran thrusts. In order to complement this new GPS velocity field with spatially dense measurements, we processed a set of ERS radar images by the radar interferometry (InSAR) technique. We used both a ‘stacking’ and a ‘persistant-scatterers’ approach to differentiate the ground deformation signal which spatial gradient is expected to be very low, from the atmospheric signal. Results from these interferograms appear to be relatively in agreement with the GPS-determined strain distribution. Nevertheless, they confirm the absence of any superficial creep behaviour since no sharp discontinuity on interferometric phase can be noted on any interferogram. Finally, we use a purely kinematic ‘block model’ inversion process to calculate slip rates and locking depths for each fault system from our GPS measurements. These models suggest that the relative quiescence over the last 200 yr has certainly produced a slip deficit as high as 2 m. So, we may wonder if the MZP fault system is not late in the interseismic phase of its earthquake cycle.
Highlights
The convergence of the Arabian and Eurasian plates, geodetically estimated to about 23 mm yr−1 in N10◦E direction in theC 2009 The Authors Journal compilation C 2009 RASHormuz Strait (e.g. Vernant et al 2004; Reilinger et al 2006), is almost completely accommodated within the Iranian borders in the Zagros, Alborz and Kopet-Dahg mountain belts (e.g. Jackson & McKenzie 1984, 1988; Jackson et al 1995)
Context, the Hormuz Strait is especially interesting since it is a transition zone between the continental collision of the Zagros and the subduction of an oceanic part of the Arabian Plate beneath the Makran wedge (Fig. 1)
We decided to complement this network with four dense GPS profiles across the MZP and SKJ fault systems in order to determine their respective role in the strain accommodation
Summary
The convergence of the Arabian and Eurasian plates, geodetically estimated to about 23 mm yr−1 in N10◦E direction in theC 2009 The Authors Journal compilation C 2009 RASHormuz Strait (e.g. Vernant et al 2004; Reilinger et al 2006), is almost completely accommodated within the Iranian borders in the Zagros, Alborz and Kopet-Dahg mountain belts (e.g. Jackson & McKenzie 1984, 1988; Jackson et al 1995). Hormuz Strait (e.g. Vernant et al 2004; Reilinger et al 2006), is almost completely accommodated within the Iranian borders in the Zagros, Alborz and Kopet-Dahg mountain belts Jackson & McKenzie 1984, 1988; Jackson et al 1995) Within this tectonic context, the Hormuz Strait is especially interesting since it is a transition zone between the continental collision of the Zagros and the subduction of an oceanic part of the Arabian Plate beneath the Makran wedge (Fig. 1). The MZP fault system transfers deformation from the Zagros towards the Makran wedge, while the SKJ fault system transfers deformation northward in the Alborz and Kopet-Dahg mountain belts, via the large dextral strike-slip fault system of Nayband and Gowk (Regard et al 2004, 2005). The obliquity of convergence with respect to mean fault strike, roughly trending N to N160◦E, indicates a transpressive tectonic context
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