Earthquake Source parameters and their scaling for the uttarakhand region of north-west himalaya

The Uttarakhand region of North-West Himalaya exhibits high historic and instrumental seismicity as evidenced by the occurrence of several moderate to large-sized earthquakes in the region. Source parameters of 16 small and moderate-sized earthquakes (3.1=Mw=6.7) have been estimated and a scaling law for the region has been developed. In this study software EQK-SRC-PARA33 has been used that considers Brune's model that yields a fall-off of 2 beyond corner frequencyfc with high frequency dimunition factor presented by Boore7 to estimate fmax. The estimated seismic moments range from 5.1×1013 to 1.10×1019Nm. The source radii are confined between 200 m to 9.7km, the stress drop ranges between 2.59MPa to 8.34MPa respectively. Using the data set of 16 events, a scaling law, M0 fc 3 = 3.0 x 1016 Nm/s3 has been developed for the region. From the plot between seismic moment and fmax, the values of fmax seem to be dependent on the source size and vary from 4 Hz to 18 Hz at various sites falling in the Uttarakhand region of NW Himalaya. Comparing the average stress drop of 6.0 MPa obtained in the present study, with the global average of 3.0 MPa for inter-plate earthquakes, it can be inferred that the average stress drop associated with the small and moderate earthquakes is almost double in the Uttarakhand region of NW Himalaya. The estimates of stress drops, fmax and scaling law will help to simulate strong ground motion using stochastic methods for this region.