Estimation of source parameters of local earthquakes near Koldam, Himachal Himalaya, India

The Koldam site is located in the Himachal Lesser Himalaya in the vicinity of the main boundary thrust. The area near Koldam is seismically active, with earthquakes ranging in size from mild to major. Earthquakes result in the death and destruction of people and property. It is vital to research the features and nature of earthquake sources. This paper examines an analysis of 45 local earthquakes that were observed in the Himachal Himalaya region during the period from June 2014 to May 2019. The seismic moment, source radius, and stress drop are among the source parameters that are computed for earthquakes. These source parameters are computed using the hypocenter parameters, corner frequency ( \({f}_{\text{c}}\) $f_{\text{c}}$ ), and low-frequency spectral level ( \({\Omega }_{\text{o}}\) ${\mathrm{\Omega }}_{\text{o}}$ ) with the help of Seisan software following Brune’s source model which describes the displacement amplitude spectrum as the physical process that releases energy at the source. This study is used to monitor and interpret the characteristics of the regional seismicity. The seismic moment ranges between 7.94 × \({10}^{10}\) ${10}^{10}$ and 1.25 × \({10}^{15}\) ${10}^{15}$ N-m with magnitudes between 1.6 and 4. The source radius is found to vary from 122.3 to 427.2 m. The stress drops of most of the events vary from 0.45 to 74.92 bar except for two events which have stress drops of 130.56 bar and 175.06 bar, respectively. Stress drops of 19 events range from 0.45 to 10.83 bar with M_o between 1 × 10¹² and 8 × 10¹² N-m, stress drops of 18 events range from 2.5 to 39.41 bar with M_o between 1 × 10¹³ and 8 × 10¹³ N-m, and stress drops of 6 events range from 18.08 to 74.92 bar with M_o between 1 × 10¹⁴ and 4 × 10¹⁴ N-m, respectively. Stress drops exhibit an increasing tendency up to a focal depth of 20 km, beyond which they show a decreasing pattern that appears to be associated with the strength of the crust. It appears that below 20 km, the strength of the upper crust decreases based on the variation of the maximum stress drop with focal depth. A scaling relationship has been established between the source parameters and the magnitudes for the region. A scaling law \({M}_{\text{o}}\) $M_{\text{o}}$ = 3.85 × \({10}^{15}{f}_{\text{c}}^{-3.068}\) ${10}^{15}{f}_{\text{c}}^{-3.068}$ has been developed between the seismic moment and corner frequency, for the region. This law almost agrees with that of the Kameng region ( \({M}_{\text{o}}\) $M_{\text{o}}$ = 2.0 ×  \({10}^{15}{f}_{\text{c}}^{-3.34}\) ${10}^{15}{f}_{\text{c}}^{-3.34}$ ) of the Arunachal Lesser Himalaya, the Bilaspur region ( \({M}_{\text{o}}\) $M_{\text{o}}$ = 2.0 ×  \({10}^{15}{f}_{\text{c}}^{-3.03}\) ${10}^{15}{f}_{\text{c}}^{-3.03}$ ) of the Himachal Lesser Himalaya, and the Garhwal Himalaya ( \({M}_{\text{o}}\) $M_{\text{o}}$ = 3.0 ×  \({10}^{16}{f}_{\text{c}}^{-3.0}\) ${10}^{16}{f}_{\text{c}}^{-3.0}$ ).