Stress pattern in the southern termination of Nehbandan fault system from inversion of earthquake focal mechanism solutions: Rigan area

Within the central and eastern parts of the Iranian plateau, active deformations follow the present-day NE-direction of compression. During 2010-2011, two earthquakes with the sinistral and dextral kinematics occurred in Rigan located at the southern edge of the Lut Block in eastern Iran. They were related to the activation of two strike-slip faults with no previous surface rupture. These two faults are NE-SW East Chah-Ghanbar and NW-SE South Chah-Ghanbar faults. Based on the dominant regional stress regime through eastern Iran, a reverse movement rather than sinistral kinematic is suggested along the NWstriking South Chah-Ghanbar fault. To investigate such an inconsistency, we studied the state of local stresses along the major fault systems surrounding the Lut Block, by the inversion of 99 focal mechanism solutions related to 74 earthquakes (1933 to 2018, Mw ≥ 4.8). The inversion results indicate a gradual deflection in the direction of the maximum horizontal compression (σ1) along the Nehbandant fault system, from north to south that includes the Dasht-e-Bayaz: N044°E, the Nehbandan: N051°E, the Kahurak: N066°E, and the Rigan: N077°E. However, there is a sharp change between the state of stress within the Rigan area and that of the Sahdad – Bam area (N013-26°E) at its western part. Based on the obtained stress pattern, it seems that among different controllers on the deflection of the regional stress, the southern splays of the active deepseated strike-slip Nehbandan fault system have a significant role. The obtained stress pattern suggests that the Rigan area is structurally part of the southern termination of the East Lut fault system. This study highlights the role of the deep-seated Nehbandan fault and its termination on the deflection of the regional stress and accommodation of deformation in eastern Iran.