Estimation of Earthquake Source Parameters in the Kachchh Seismic Zone, Gujarat, India, from Strong-Motion Network Data Using a Generalized Inversion Technique

The generalized inversion of S -wave spectral amplitude data from 18 strong-motion sites in the Kachchh seismic zone, Gujarat, India, has been carried out to estimate source parameters of 38 aftershocks ( M w 2.93–5.32) from the 2001 Bhuj earthquake ( M w 7.7). The result shows that the seismic moment M and source radius r of aftershocks are between 3.1×1013 and ![Graphic][1] and 226–889 m, respectively, while stress drops ( Δσ ) vary from 0.11 to 7.44 MPa. The regression analysis between M and r shows a break in linear scaling at ![Graphic][2] . The estimated stress-drop values scatter significantly with M (![Graphic][3] ) for larger aftershocks (![Graphic][4] ) but vary in proportion with M (![Graphic][5] ) in case of smaller magnitude events. This can be due to the complex rupture process associated with relatively larger aftershocks in comparison to circular rupture for smaller events. The high stress-drop values are observed for events located on the north Wagad fault (at 15–30 km depths) and Gedi fault (at 0–5 km depths). This could be attributed to the large stress develop at the hypocentral depth as a result of high pore-fluid pressure beneath these two fault zones. The regression between M and corner frequency f c shows M is proportional to ![Graphic][6] , which is consistent for earthquakes with short rupture lengths and high stress-drop values. High stress-drop values commonly associated with the events from Kachchh and adjacent Narmada-Son lineament rift zones indicate strong potential for generating high peak ground accelerations and hence high seismic hazard. [1]: /embed/inline-graphic-1.gif [2]: /embed/inline-graphic-2.gif [3]: /embed/inline-graphic-3.gif [4]: /embed/inline-graphic-4.gif [5]: /embed/inline-graphic-5.gif [6]: /embed/inline-graphic-6.gif