Source Characterisation of February 06, 2017 Rudraprayag Earthquake in Northwest Himalaya and Ground Motion Prediction for a Scenario Earthquake (Mw 6.8)

Abstract

We have studied a moderate earthquake of February 06, 2017 occurred in Rudraprayag, Uttarakhand of northwest Himalaya that created prominent ground shakings not only around the epicentral region but also to far distances in different parts of the National Capital Territory (NCT) of Delhi, which is an unusual experience. Full waveform inversion and source study suggest, moment magnitude of the event to be Mw 5.5 with the centroid depth of 19 km. The waveform analysis also reveals the oblique faulting mechanism associated with the down-dip apex of the detachment. The source parameters, namely, source radius, stress drop, and seismic moment of the event have been estimated to be 2.3 km, 63 bars, and 2.05 E + 17N-M respectively. The epicenter of the event falls in the seismically active zone between two major thrusts of the Himalaya, viz., Main Boundary Thrust (MBT) and Main Central Thrust (MCT). In the present study, strong ground motion was simulated using Empirical Green’s Function (EGF) approach for a scenario earthquake of Mw6.8 magnitude in the same source, considering it similar to the Chamoli earthquake (M 6.8) of March 29, 1999 that had occurred in the neighborhood. The peak ground acceleration (PGA) has been estimated at the recording sites and a contour map is generated for the entire study region, covering the cities located up to ∼ 700 km from the source. The predicted strong ground motion varies between 22 gals to 352 gals within the epicentral region up to ∼ 150 km, which may lead to moderate to severe ground shaking. However, weak to light shaking expected in the remaining parts of the study region with PGA ranging between (0.50–22) gals.