Abstract
We have successfully detected widely distributed ground displacements for the 2015 Gorkha earthquake by applying a ScanSAR-based interferometry analysis of Advanced Land Observing Satellite 2 (ALOS-2) L-band data. A major displacement area extends with a length of about 160 km in the east-west direction, and the most concentrated crustal deformation with ground displacement exceeding 1 m is located 20–30 km east from Kathmandu. A quasi-vertical displacement estimated by combining the ascending and the descending data indicates upheaval of about 1.4 m at maximum. We inverted the synthetic aperture radar interferometry (InSAR) data including both of the main shock (moment magnitude (Mw) 7.8) and the largest aftershock (Mw 7.3) to construct a slip distribution model. Our model shows a nearly pure reverse fault motion with a slip amount of approximately 6 m at maximum, and the spatial extent is zonally distributed within a distance of 50 to 100 km from the surface along downdip direction. The downdip end of the slip is quite consistent with that of the interseismic coupling area geodetically inferred in previous studies. On the other hand, there is no significant slip at shallow depth in spite of the fact that the plate interface is thought to be fully locked there, may be suggesting that there still remains a potential of fault slip. The slip distribution unnaturally bifurcates in the east, and we can identify a clear-cut slip deficit area with a radius of ~10 km just west side of the Mw 7.3 event, where the slip amount reaches only 20 cm at most. This area is presumably subjected to a strong shear stress which should promote a reverse fault slip. There is a possibility to produce a fault slip equivalent to Mw ~7.0 in the future although we do not know if the slip heterogeneity would be smoothed out by a seismic event or an aseismic event.
Highlights
A devastating earthquake with a moment magnitude (Mw) of 7.8 (US Geological Survey 2015) struck central Nepal on April 25, 2015, with its hypocenter located in the Gorkha region, called Gorkha earthquake
The primary purpose of this paper is to rapidly report the whole picture of the 2015 Gorkha earthquake with showing crustal deformation and the fault slip distribution inferred from the ScanSAR-based InSAR data
To pick up the crustal deformation only, we reduced the noises by the following steps
Summary
A devastating earthquake with a moment magnitude (Mw) of 7.8 (US Geological Survey 2015) struck central Nepal on April 25, 2015, with its hypocenter located in the Gorkha region, called Gorkha earthquake. A thrust fault with a NNE–SSW compressive axis was inferred from some seismic wave analyses (Fig. 1); vertical and NS-oriented ground movements associated with the reverse motion must have been involved in the ground surface changes. This earthquake is the largest event in Nepal since the 1934 Bihar-Nepal earthquake (Mw 8.1) (Ambraseys and Douglas 2004; Avouac 2007). The aftershock distribution, including five seismic events of >M6, extended east of a hypocenter of the main shock (Fig. 1), and a Mw 7.3 aftershock occurred approximately 150 km east of the hypocenter of the main shock on 12 May 2015 This event has a thrust fault mechanism and is the largest aftershock as of this writing
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