Analysis of strong-motion characteristics of the 2015 Gorkha, Nepal,Earthquake

In this paper, we use the acceleration data at KATNP station, about 11 km from the seismogenic fault, which completely recorded the acceleration time history of the main shock of Gorkha earthquake that occurred in Gorkha district of Nepal on April 25, 2015, to analyze its ground motion characteristics. The results of our research show that at KATNP station, the horizontal peak ground acceleration (PGA) is 0.23 g, and the vertical PGA is 0.19 g. Those values are less than the ones expected by researchers, which was preliminary speculated by Dixit et al.(2015) that this may be caused by the nonlinear response of the Kathmandu valley. Gorkha earthquake caused permanent surface displacement at KATNP station, of which the horizontal displacement is 159.2 cm, the direction is 199 degrees, and the vertical displacement is 131.9 cm. According to those calculated results, we can simply determine the fault strike is 289 degrees(109 degrees). The possible reasons which cause pulse-like ground motions are the basin effect, the rupture forward directivity and the fling step, of which the period of basin effect is about 5 s, and the period of forward directivity pulse is about 8 s. There are two peak values at about 0.5 s and 5.0 s on the acceleration response spectrum; the former is due to rich high frequency ground motion caused by the pulse-type sliding of earthquake rupture, the latter is due to the basin effect and the rupture forward directivity. The duration of strong ground motion is about 36 similar to 46 s based on Arias intensity, less than the one caused by the earthquake of comparative size, and the duration of earthquake ground motion in different directions are likely related to the direction of earthquake rupture. Arias intensity changing over time also reflects that the Gorkha earthquake rupture time history is relatively simple, suggesting an uninterrupted rupture.