The Significance of Strike‐slip Faulting in the Basement of the Zagros Fold and Thrust Belt

Abstract

Lateral ofsets in the pattern of seismicity along the Zagros fold and thrust belt indicate that transverse faults segmenting the Arabian basement are active deep-seated strike-slip faults. The dominant NW-SE trending features ofthe belt have undergone repeated horizontal displacements along these transverse faults. These reactivated basement faults, which are inherited from the Pan-African construction phase, controlled both deposition of the Phanerozoic cover before Tertiary-Recent deformation of the Zagros and probably the entrapment of hydrocarbons on the NE margin of Arabia and in the Zagros area. We have used observations of faulting recognized on Landsat satellite images, in conjunction with the spatial distribution of earthquakes and their focal mechanism solutions, to infer a tectonic model for the Zagros basement.Deformation in the NW Zagros appears to be concentrated on basement thrusts and a few widely-spaced north-south trending strike-slip faults which separate major structural segments. In the SE Zagros, two main structural domains can be distinguished. A domain of NNWtrending right-lateral faults in the northern part of the SE Zagros implies that fault-bounded blocks are likely to have rotated anticlockwise about vertical axes relative to both Arabia and Central Iran. In contrast, the predominance of NNE-trending left-lateral faults in the southern part of the SE Zagros implies that fault-bounded blocks may have rotated clockwise about vertical axes. We propose a tectonic model in which crustal blocks bounded by strike-slip faults in a zone of simple shear rotate about vertical axes relative to both Arabia and Central Iran. The presence of domains of strike-slip and thrust faulting in the Zagros basement suggest that some of the convergence between Arabia and Central Iran is accommodated by rotation andpossible lateral movement of crust along the belt by strike-slip faults, as well as by obvious crustal shortening and thickening along thrust faults.

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

“…It has previously been suggested that the Balarud Line represents a region of strike-slip faulting (e.g. Berberian 1995;Hessami et al 2001). However, in agreement with Talebian & Jackson (2004) we find that the earthquakes in this region represent thrust-faulting, so it seems unlikely that the Balarud Line represents a region of active strike-slip faulting.…”

Estructura neógena de la Precordillera Andina, Argentina: aportes de modelos análogos.

“…These results are consistent with several proposals (Flinch and Casas, 1996;Pohn, 2001;Japas et al, 2010;Oriolo, 2012;Oriolo et al, 2013) where cross-strike structures are described as pre-existing crustal fabrics. Moreover, similar geometrical and kinematical relationships between dextral shear zones and secondary oblique sinistral ones were presented by theoretical models of Jiang (1994) and examples from the Zagros fold and thrust belt (Hessami et al, 2001), the Atacama fault system (Cembrano et al, 2005) and the Cap de Creus (Carreras et al, 2013). However, oblique ENE-trending structures do develop even though previous structures are not present (Fig.…”

Probabilistic seismic hazard maps for the sultanate of Oman

“…Moderate to large earthquakes frequently occur but rarely exceed M W = 7.0. Recently determined focal depths (8-14 km) imply that moderate to large earthquakes occur in the uppermost part of the Arabian basement (Ni and Barzangi 1986;Baker et al 1993;Hessami et al 2001;Hatzfeld et al 2010). Focal mechanism solutions (Fig.…”