Large earthquakes are thought to release strain on previously locked faults. However, the details of how earthquakes are initiated, grow and terminate in relation to pre-seismically locked and creeping patches is unclear. The 2015 M w 7.8 Gorkha, Nepal earthquake occurred close to Kathmandu in a region where the prior pattern of fault locking is well documented. Here we analyse this event using seismological records measured at teleseismic distances and Synthetic Aperture Radar imagery. We show that the earthquake originated northwest of Kathmandu within a cluster of background seismicity that fringes the bottom of the locked portion of the Main Himalayan Thrust fault (MHT). The rupture propagated eastwards for about 140 km, unzipping the lower edge of the locked portion of the fault. High-frequency seismic waves radiated continuously as the slip pulse propagated at about 2.8 km s-1along this zone of presumably high and heterogeneous pre-seismic stress at the seismic-aseismic transition. Eastward unzipping of the fault resumed during the Mw 7.3 aftershock on 12 May. The transfer of stress to neighbouring regions during the Gorkha earthquake should facilitate future rupture of the areas of the MHT adjacent and updip of the Gorkha earthquake rupture.
Bullard Laboratories, Department of Earth Sciences, University of Cambridge, Madingley Road, Cambridge, United Kingdom; Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, 595 Charles Young Drive East, Box 951567, Los Angeles, CA, United States; Earth Observatory of Singapore, Nanyang Technological University, N2-01A-108, 50 Nanyang Avenue, Singapore, Singapore; Huffington Department of Earth Sciences, Southern Methodist University, PO Box 750395, Dallas, TX, United States; Seismological Laboratory, Geology and Planetary Science Division, California Institute of Technology, 1200 E. California Boulevard, Pasadena, CA, United States
Recommended Citation:
Avouac J.-P.,Meng L.,Wei S.,et al. Lower edge of locked Main Himalayan Thrust unzipped by the 2015 Gorkha earthquake[J]. Nature Geoscience,2015-01-01,8(9)