Earthquake Source Parameters of Moderate to Small Earthquake and Scaling Relationships in the Western Himalaya: Seismic Hazard Implication

The Northwest Himalayas experiences frequent seismic activity, with numerous moderate events occurring over the past century, leading to several disasters. In the present study, we conducted a comprehensive analysis of the source parameters for 125 earthquakes with local magnitudes (ML) ≥ 4.0 that occurred in the northwest region during the period from 2013 to 2019. We analyzed the P and S wave spectra using Brune's source model to investigate the self-relation and self-similarity of earthquakes in the area. The digital seismograms used in this study were recorded by sixteen permanent broad-band stations at hypocentral distances between 10 and 327 km. The average ratio of P/S wave corner frequency is found in the range of 1.1-1.9, suggesting a higher corner frequency for the P wave. The static stress drops range from 0.1 and 136 MPa with a median value of 9.8 MPa (98 bars). The obtained seismic moments range from 7.49×10<sup>14</sup> to 1.15×10<sup>18</sup> Nm (4.0 ≤ Mw ≤ 6.0). The source radii are between 388 and 7073 m. we established a linear relationship between local and moment magnitudes. The scaling relations obtained indicated a slight deviation from self-similarity. High-stress drops observed in some events suggest elevated frictional strength and lower strain rates within faults, while lower stress drops may indicate general fault weakness. Although a definitive correlation between seismic moment and static stress drop was not observed universally, some events with lower seismic moment values also demonstrated lower stress drops. Furthermore, the corner frequency decreased with increasing seismic moment, with a slight depth dependence observed; shallower events tended to have higher corner frequency values than deeper ones. While there wasn't a clear depth dependence of stress drop values, a more pronounced depth dependence of seismic moment was observed, indicating that deeper events generally have larger seismic moment values in our study area. This implies that large earthquakes could still leave significant stress on faults, potentially leading to future events. The present study also reveals that Mw is lower than ML for all earthquakes with magnitudes > 4.0. The coefficient of determination of the magnitude fit scale is found to be 0.91, which indicates the fit is good. Therefore, it is concluded that the newly derived magnitude scale is more consistent than the currently used ML scale for the study region.