The Qp attenuation structure of the Koyna-Warna region, Maharashtra India, and its correlation to seismicity

In this study, we developed a three-dimensional (3D) (Qp) P-wave attenuation model of the uppermost crust (0-10 km depth) of the Koyna-Warna region (India). The inversion of attenuation operator (t*) is used to deduce a 3D Qp attenuation model using simul2000 code by assuming that t* is independent of frequency. A total of 276 earthquakes (1.0 <= ML <= 3.5) were used for this study, those providing 2045 t* values. The t* values are determined by fitting the observed P-wave amplitude spectrum with the theoretical spectrum by assuming an omega 2 source model using a nonlinear least squares spectral-fitting algorithm. The tomography model shows the low Qp anomalies (similar to 200-350) at shallow depth (0-3 km) that could be related to fracturing and cracks. The Qp value gradually increases with depth due to the closure of cracks and fractures as pressure increases from the lithostatic load. The high Qp (similar to 500-600) are found in the intense seismic activity zone at 5-7 km depth where majority of the earthquakes were generated corresponds to the brittle crust and well correlated to higher Vp (similar to 5.5-6.0 km/s) reported previously in the study area. We inferred that the high Qp is well correlated to seismicity likely associated with the dry to partially saturated rocks, which playing a vital role in the genesis of earthquakes in the study area.