The 2007 Talala, Saurashtra, western India earthquake sequence: Tectonic implications and seismicity triggering

Abstract: A damaging and widely felt moderate (Mw 5.0) earthquake occurred in the Talala region of Saurashtra, Gujarat (western India) on November 6, 2007. The highly productive sequence comprised about 1300 micro earthquakes (M >0.5) out of which 325 of M ⩾1.5 that occurred during November 6, 2007–January 10, 2008 were precisely located. The spatial aftershock distribution revealed a NE–SW striking fault in accordance with the centroid moment tensor solution, which in turn implies left-lateral motion. The orientation and sense of shear are consistent with similarly orientated geological fault identified in the area from satellite imagery and field investigation. The aftershocks temporal decay, b-value of frequency–magnitude distribution, spatial fractal dimension, D, and slip ratio (ratio of the slip occurred on the primary fault to the total slip) were examined with the purpose to identify the properties of the sequence. The high b-value (1.18±0.01) may be attributed to the paucity of the larger (M ⩾4.0) aftershocks and reveals crustal heterogeneity and low stress regime. The high p-value (1.10±0.39), implying fast decay rate of aftershocks, evidences high surface heat flux. A value of the spatial fractal dimension (D) equal to 2.21±0.02 indicates random spatial distribution and source in a two-dimensional plane that is being filled-up by fractures. A slip ratio of 0.42 reveals that more slip occurred on secondary fault systems. The static Coulomb stress changes due to the coseismic slip of the main shock, enhanced off fault aftershock occurrence. The occurrence of a moderate earthquake (Mw 4.3) on October 5, 2008 inside a region of positive Coulomb stress changes supports the postulation on aftershock triggering. When the stress changes were resolved on a cross section including the stronger (M4.8) foreshock plane that is positioned adjacent to the main fault, it became evident that the activity continued there due to stress transfer from the main rupture. [Copyright &y& Elsevier]