Source parameters and scaling relations for small earthquakes in the Saurashtra Horst of Western Deccan Volcanic Province, India and its seismotectonic implications

The Saurashtra Horst, south of the Kachchh Rift Basin, is a significant tectonic block in the northwestern Deccan Volcanic Province of India. The Saurashtra Horst belongs to the stable continental region and typically experiences shallow intraplate earthquakes with depths up to 20 km. We analysed spectra of P- and S-waves using 182 broadband seismograms from 40 small earthquakes ( M 3.5–5.1). It has been observed that there is a shift in P-wave corner frequency for most earthquakes to the higher side compared to that of S-corner frequency in both regions. The seismic moments measured from primary waves, i.e., M 0 ( P ), vary from 7.7 × 10 12 to 5.88 × 10 16 N-m, and from secondary waves, i.e., M 0 ( S ) range from 1.52 × 10 13 to 1.88 × 10 17 N-m for the southern part of Saurashtra. The corresponding variation of seismic moments for the events in northern Saurashtra is 3.08 × 10 12 to 4.50 × 10 14 N-m for P-waves and 7.01 × 10 12 to 2.34 × 10 15 N-m for S-waves. The estimated stress drop values lie in the range of 0.02–20.08 bars and 0.01–9.09 bars for the earthquakes in Saurashtra’s southern and northern parts, respectively. The small earthquakes have been found to be self-similar in the southern part, while there is a breakdown of self-similarity for small earthquakes in the northern region. This indicates the diverse stress regimes in the Saurashtra Horst. A scaling relation ( M_0f^3_c = 2.19×10^15 N-m/s^3 ) for the southern part of Saurashtra is obtained during the linear regression investigation among the established seismic moment, i.e., M 0 , and corner frequency, i.e., f c . The structural heterogeneities corroborate the diversity in source parameters for two different parts of SH in the regions. The variability of stress drops for the best-located events shows that the higher stress drop values correspond to the source zone having lower Vp/Vs and vice versa.