Shallow Structure of the Main Himalayan Thrust from Relocated 2015 MW7.8 Gorkha, Nepal Aftershocks

Abstract:

On 25 April 2015 the M_W 7.8 Gorkha, Nepal earthquake ruptured a shallow section of the Main Himalayan Thrust (MHT) near the capital city of Kathmandu. A temporary broadband seismograph array we deployed near the China-Nepal border recorded the Gorkha earthquake and its aftershocks. Using teleseimic P waveform modeling and multi-scale double-difference earthquake relocation methods for the locally, regionally and teleseismically recorded events, we relocated 153 Gorkha earthquakes with M_W>3.5. In addition, 43 earthquakes with M_W>3.0 that occurred in the source region during three decades prior to the Ghorka earthquake were also relocated. The results of the study provide refined hypocenters with good depth constraints. From the aftershock data, we can see the shallowly dipping fault structure for the MHT, as well as other structures in the hanging wall of the fault zone.

This is the first well-recorded earthquake sequence that has occurred on the shallowest portion of the MHT, providing new constraints on the structure of the MHT and its earthquake potential along the Himalaya orogen.