The 2001 M w 7.6 Bhuj earthquake, low fault friction, and the crustal support of plate driving forces in India

We present a source model for the 2001 M w 7.6 Bhuj earthquake of northwest India. The slip distribution suggests a high stress drop (∼35 MPa) and, together with the depth distribution of aftershocks, that the entire crust is seismogenic. We suggest that the active faults have an effective coefficient of friction of ∼0.08, which is sufficient for the seismogenic crust to support the majority of the compressive force transmitted through the Indian lithosphere. This model is consistent with the midcrustal depth of the transition from extension to compression beneath the Ganges foreland basin where India underthrusts southern Tibet. If the coefficient of friction were the more traditional value of 0.6, the lithosphere would be required to support a net force roughly an order of magnitude higher than current estimates in order to match the observed depth of the neutral fiber.