INCOMPLETE DÉCOLLEMENT RUPTURE IN THE 25 APRIL 2015 GORKHA EARTHQUAKE: IMPLICATIONS FOR POSTSEISMIC PROCESSES

The failure of the 2015 Gorkha earthquake to completely rupture the Himalayan décollement from the southern edge of Tibet to the faults fronting the Himalayan foothills (MFT), raises several issues concerning the future evolution of stresses now imposed in the lesser Himalaya at the latitude of Kathmandu. InSAR imagery and coseismic GPS measurements indicate that slip in the main rupture has imposed a tapered slip distribution near the rupture’s southern edge at approximately 10 km depth, 30 km north of the MFT. Shortly after the earthquake new GPS instruments were installed, bringing the number of instruments monitoring the western and southern edge of the Gorkha rupture to 15. In the first two months following the earthquake we observed slow continued southward displacements above the southern edge of the rupture at rates of 10-20 mm/yr, an order of magnitude larger than interseismic rates at these latitudes, which would dissipate the current slip deficit in ≈50 years. Preliminary forward models of afterslip and viscous response to the main rupture provide bounds on the strain partitioning among mechanisms and the potential stress changes on adjacent unslipped fault segments, including the 1505 rupture immediately to the west.