An improved geodetic source model for the 1999 Mw 6.3 Chamoli earthquake, India

Abstract

We present a distributed slip model for the 1999 Mw 6.3 Chamoli earthquake of north India using interferometric synthetic aperture radar (InSAR) data from both ascending and descending orbits and Bayesian estimation of confidence levels and trade-offs of the model geometry parameters. The results of fault-slip inversion in an elastic half-space show that the earthquake ruptured a 9°+3.4-2.2 northeast-dipping plane with a maximum slip of ~1 m. The fault plane is located at a depth of~15.9+1.1-3.0 km and is~120 km north of the Main Frontal Thrust, implying that the rupture plane was on the northernmost detachment near the mid-crustal ramp of the Main Himalayan Thrust. The InSAR-determined moment is 3.35 × 1018 Nm with a shear modulus of 30 GPa, equivalent to Mw 6.3, which is smaller than the seismic moment estimates of Mw 6.4-6.6. Possible reasons for this discrepancy include the trade-off between moment and depth, uncertainties in seismic moment tensor components for shallow dip-slip earthquakes and the role of earth structure models in the inversions. The released seismic energy from recent earthquakes in the Garhwal region is far less than the accumulated strain energy since the 1803 Ms 7.5 earthquake, implying substantial hazard of future great earthquakes.