Slip kinematics and ground motions of the 2015 Mw7.8 Gorkha, Nepal earthquake imaged with 5Hz GPS data and ALOS-2 InSAR constraints

Thursday, 17 December 2015: 08:30
305 (Moscone South)
John Galetzka1, Diego Melgar2, Joachim F Genrich3, Jianghui Geng4, Susan E Owen5, Eric O Lindsey6, Xiaohua Xu6, Prithvi Lal Shrestha7, Lok Bijay Adhikari7, Yehuda Bock4 and Jean-Philippe Avouac8, (1)UNAVCO, Inc. Boulder, Boulder, CO, United States, (2)University of California Berkeley, Berkeley, CA, United States, (3)California Institute of Technology, Pasadena, CA, United States, (4)University of California San Diego, La Jolla, CA, United States, (5)NASA Jet Propulsion Laboratory, Pasadena, CA, United States, (6)Scripps Institution of Oceanography, La Jolla, CA, United States, (7)Nepal Department of Mines and Geology, Kathmandu, Nepal, (8)California Institute of Technology, Geological and Planetary Sciences, Pasadena, CA, United States
We present kinematic slip inversion results of the April 25, 2015 Mw 7.8 Gorkha, Nepal earthquake from the joint inversion of 5Hz GPS data and ALOS-2 interferograms. This detailed geodetic imaging of earthquake rupture enhances our understanding of earthquake physics and induced ground shaking, the Gorkha earthquake is the first example of a large continental megathrust rupture beneath a high-rate (5 Hz) GPS network. Coupled with new ALOS-2 InSAR data collected in ScanSAR mode which covers the entire mainshock in a single pass we obtain an unprecedented view of the event purely with space geodesy. We produce source time functions for all the event subfaults and find the earthquake ruptures predominantly as a slip pulse of ~20 km width, with slow slip onset, peak sliding velocity of ~1 m/s and ~6 s duration. It propagated toward Kathmandu basin at ~3 km/s over ~140 km. We will discuss in detail the inversion technique and efforts to validate the results which show the slip distribution and smooth onset of slip to be a robust feature of the inversion. The smooth slip onset, indicating a large ~5 m slip-weakening distance, caused moderate ground shaking at high >1Hz frequencies (~16% g) and limited damage to regular dwellings. With high-rate GPS data in and around Kathmandu and a strong motion sensor we also analyze ground motions within the city and find whole basin resonance at 4-5 s period, consistent with the slip pulse characteristics, which caused collapse of tall structures, including cultural artifacts.