Comparison of earthquake source characteristics in the Kachchh Rift Basin and Saurashtra horst, Deccan Volcanic Province, western India

Seismic source parameters of small to moderate sized intraplate earthquakes that occurred during 2002–2009 in the tectonic blocks of Kachchh Rift Basin (KRB) and the Saurashtra Horst (SH), in the stable continental region of western peninsular India, are studied through spectral analysis of shear waves. The data of aftershock sequence of the 2001 Bhuj earthquake ( M_w 7.7) in the KRB and the 2007 Talala earthquake ( M_w 5.0) in the SH are used for this study. In the SH, the seismic moment ( M_o) , corner frequency (f_c) , stress drop ( σ ) and source radius ( r ) vary from 7.8× 10^11 to 4.0× 10 ^16 N-m, 1.0–8.9 Hz, 4.8–10.2 MPa and 195–1480 m, respectively. While in the KRB, these parameters vary from M_o∼ 1.24 × 10^11 to 4.1 × 10^16 N-m, f_c ∼ 1.6 to 13.1 Hz, σ∼ 0.06 to 16.62 MPa and r ∼ 100 to 840 m. The kappa ( K ) value in the KRB (0.025–0.03) is slightly larger than that in the SH region (0.02), probably due to thick sedimentary layers. The estimated stress drops of earthquakes in the KRB are relatively higher than those in SH, due to large crustal stress concentration associated with mafic/ultramafic rocks at the hypocentral depths. The results also suggest that the stress drop value of intraplate earthquakes is larger than the interplate earthquakes. In addition, it is observed that the strike-slip events in the SH have lower stress drops, compared to the thrust and strike-slip events.