Abstract
The 2015 Gorkha earthquake and its aftershocks caused severe damage mostly in Nepal, while countries around the Himalayan region were warned for decades about large Himalayan earthquakes and the seismic vulnerability of these countries. However, the magnitude of the Gorkha earthquake was smaller than those of historical earthquakes in Nepal, and the most severe damage occurred in the north and northeast of Kathmandu. We explore reasons for these unexpected features by performing a joint source inversion of teleseismic, geodetic, and near-field waveform datasets to investigate the rupture process. Results indicate that the source fault was limited to the northern part of central Nepal and did not reach the Main Frontal Thrust. The zone of large slip was located in the north of Kathmandu, and the fault rupture propagated eastward with an almost constant velocity. Changes in the Coulomb failure function (ΔCFF) due to the Gorkha earthquake were computed, indicating that southern and western regions neighboring the source fault are potential source regions for future earthquakes related to the Gorkha earthquake. These two regions may correspond to the historical earthquakes of 1866 and 1344. Possible future earthquakes in the regions are predicted, and the warning for Himalayan seismic hazards remains high even after the Gorkha earthquake.
Highlights
Around Nepal, the Indian and Eurasian plates collide, and the Indian lithosphere underthrusts beneath the Eurasian plate at the Main Frontal Thrust (MFT, Fig. 1) with a convergence rate of approximately 18 mm/year (Ader et al 2012)
The hypocenter of the earthquake determined by the United States Geological Survey (USGS, http://www.usgs.gov/, accessed on April 27, 2015) was 28.1473°N, 84.7079°E, and 15 km in depth, indicating that the earthquake occurred on the Main Himalayan Thrust (MHT)
Joint source inversion Three types of datasets are available for this investigation: (1) teleseismic dataset obtained from the Global Seismographic Network (Fig. 2c) through the Data Management Center of the Incorporated Research Institutions for Seismology, (2) ground deformation dataset obtained at GPS stations (Fig. 2a) through the UNAVCO Data Center and from the InSAR image processed by Lindsey et al (2015), and (3) dataset of near-field waveforms of strong motion (Takai et al 2016) and high-rate GPS (Galetzka et al 2015) stations (Fig. 2a)
Summary
Around Nepal, the Indian and Eurasian plates collide, and the Indian lithosphere underthrusts beneath the Eurasian plate at the Main Frontal Thrust (MFT, Fig. 1) with a convergence rate of approximately 18 mm/year (Ader et al 2012). Joint source inversion Three types of datasets are available for this investigation: (1) teleseismic dataset obtained from the Global Seismographic Network (Fig. 2c) through the Data Management Center of the Incorporated Research Institutions for Seismology, (2) ground deformation dataset obtained at GPS stations (Fig. 2a) through the UNAVCO Data Center and from the InSAR image processed by Lindsey et al (2015), and (3) dataset of near-field waveforms of strong motion (Takai et al 2016) and high-rate GPS (Galetzka et al 2015) stations (Fig. 2a).
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