SOURCE CHARACTERISTICS FROM MEDIUM EARTHQUAKES AROUND KATHMANDU VALLEY BASED ON STRONG MOTION RECORDS

The Nepal-Himalayan is the earthquake-prone zone where the Indian plate is subducted into the Eurasian plate at a low angle. Investigating source characteristics in this region is important for improving the accuracy of strong ground motion evaluation of future earthquakes and seismic hazard assessment. We applied the S-coda spectral ratio method to the 2015 Gorkha Nepal earthquake aftershocks and investigated the source characteristics of the small to medium-sized earthquakes of magnitude 3.9-6.7 at the plate collision boundary around the Kathmandu Valley. The corner frequencies of the earthquakes were identified by fitting the observed source spectral ratio to the theoretical source spectral ratio based on the omega square source model, and the stress drop was estimated. We attempted to compare the estimated stress drops with the seismic moment and the focal depth. The stress drops for the aftershocks in the western region near the epicenter of the 2015 Gorkha Nepal earthquake tend to be slightly smaller than those of aftershocks in the eastern region.