Interaction between the far-field stress and crustal boundary faults in the kinematics of active deformation around the Lut Block, Eastern Iran

Abstract

We investigate the effects of far-field stresses and major crustal boundary faults in the deviation of local stresses around the Lut Block of the southeastern Iranian plateau in the light of the 2010–2011 Rigan earthquakes. Dextral 2010 (Mw 6.5) and sinistral 2011 (Mw 6.2) Rigan earthquakes occurred in the southern edge of the Lut Block, where there is no report of moderate to large magnitude historical and instrumental seismicity. To address the style and distribution pattern of local stresses, we apply the inversion method to focal mechanism solutions of 74 earthquake events (1933–2018, Mw ≥ 4.8). The data were separated into six clusters including the Tabas – Dasht-e-Bayaz, East Lut, Kahurak, Rigan, Shahdad – Bam, and West Lut – Kuhbanan zones. Moving toward the Rigan area, the results indicate a gradual deflection in the direction of the horizontal σ1 axis along the East Lut fault system (i.e., from north to south, Dasht-e-Bayaz: N044°E, East Lut: N051°E, Kahurak: N066°E, Rigan: N077°E), while it reveals a sharp change along the West Lut fault system (i.e., from north to south, Tabas: N044°E, West Lut – Kuhbanan: N010–13°E, Shahdad – Bam: N013–26°E, Rigan: N077°E). The deviation in the long-lasting strike-slip/transpressional stress regimes along the eastern and western boundaries of the Lut Block is mainly controlled by the geometry and kinematics of the East Lut fault system, and the direction of the Arabia – Eurasia convergence, respectively. The geodynamic interaction of the East and West Lut fault systems which bound the crustal block on both sides has a significant effect on the evolution of local stresses in the southern edge of the Lut Block, which is bounded by second-order faults that are the termination of the major faults. The results may apply to other crustal blocks limited in some boundaries by the second-order splays of crustal faults with different geodynamic implications.