Earthquakes on the Kazerun Line in the Zagros Mountains of Iran: strike-slip faulting within a fold-and-thrust belt

Abstract

S U M M A R YThe Kazerun Line is a transverse valley of about 200 km long that obliquely crosses the regular anticlines of the Zagros fold belt in SW Iran. At its northern end it is a clear fault which can be mapped on the surface. Anticline axes die out or bend towards this valley but do not cross it. Six moderate-sized earthquakes that occurred close the the Kazerun Line, and within a 25 km area involved right-lateral strike-slip motion parallel to the strike of the valley. They indicate that the Kazerun Line is the surface expression of a buried strike-slip fault. Slip vectors in these strike-slip earthquakes are different from those of neighbouring reverse-fault earthquakes, suggesting that the Kazerun Line accommodates some of the shortening between Arabia and central Iran by an elongation of the Zagros mountains parallel to strike. The centroid depths and the source dimensions of these earthquakes, combined with the lack of seismogenic surface faulting in the Zagros, suggest to us that all these earthquakes involve faulting in the metamorphic basement beneath the sedimentary cover. The sedimentary cover is almost certainly decoupled from the basement by several thick evaporite horizons. The seismicity of the Kazerun Line thus demonstrates how lateral interruptions to the regularity of a fold belt can arise from faulting in the basement, and not just from lateral ramps between the thrust sheets that deform the sedimentary cover.

Kinematics and surface fracture pattern of the Anaran basement fault zone in NW of the Zagros fold–thrust belt

“…Recent studies (Talbot and Alavi 1996;Bahroudi and Talbot 2003;Bahroudi and Koyi 2004;Sherkati and Letouzey 2004;Farzipour-Saein et al 2009a) show that the geometry of the Zagros deformation front and evolving foreland basin has been controlled by at least two different structural parameters: (1) reactivation of basement faults (Hessami et al 2001a;Bahroudi and Talbot 2003;Sepehr and Cosgrove 2005;Ahmadhadi et al 2007;Mouthereau et al 2007a, b;Farzipour-Saein et al 2009a;Nilfouroushan et al 2013;Burberry 2015) and (2) mechanical nature of the sedimentary layers in the ZFTB (Bahroudi and Koyi 2003;Sherkati and Letouzey 2004;Farzipour-Saein et al 2009b). Different evidences indicate that many of the transverse basement faults involve right-lateral strike-slip displacements with dip-slip components (Baker et al 1993;Berberian 1995;Hessami et al 2001b;Bahroudi and Talbot 2003;Sepehr and Cosgrove 2005;Ahmadhadi et al 2007;Farzipour-Saein et al 2009a;Allen 2010).…”

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.…”

“…The catalogue is built by merging historical and instrumental data. In addition, the following studies on specific events or region were also consulted to gather additional information regarding earthquakes of considerable size (Berberian 1973;Quittmeyer 1979;Jackson and Fitch 1981;Alsinawi 1983;Jackson and McKenzie 1984;Baker et al 1993;Berberian 1995;Berberian and Yeates 1999;Berberian et al 2001;Maggi et al 2002;Talebian and Jackson 2004;Walker et al 2005;Rodgers et al 2006;Al Marzooqi et al 2008). …”

Upliftment Estimation of the Zagros Transverse Fault in Iran Using Geoinformatics Technology

“…Safari and Chitsazan (2005) distinguished and mapped the Izeh fault zones and segmented it into four main fault segments, including the Kuh-e-Pabdeh, Andika, Baghmalek and Seidun segments [2]. The corrected pseudo-color ETM+ images were filtered by high-pass and directional-filters and consequently, the length and width of this fault zone are extracted from the images.…”

“…This fold-thrust belt is truncated and disturbed by several transverse strike-slip fault zones such as the Izeh, Kazerun, Karebas, Sarvestan and Sabzpushan fault zones [2][3][4][5] with approximately N160°-180° in trend. This seismically active fold-thrust belt is divided into the Thrust Zone (High Zagros), Simply Folded Belt (SFB) and Coastal Plain [6][7][8][9][10].…”