title: Widespread ground motion distribution caused by rupture directivity during the 2015 Gorkha, Nepal earthquake.
abstract: The ground motion and damage caused by the 2015 Gorkha, Nepal earthquake can be characterized by their widespread distributions to the east. Evidence from strong ground motions, regional acceleration duration, and teleseismic waveforms indicate that rupture directivity contributed significantly to these distributions. This phenomenon has been thought to occur only if a strike-slip or dip-slip rupture propagates to a site in the along-strike or updip direction, respectively. However, even though the earthquake was a dip-slip faulting event and its source fault strike was nearly eastward, evidence for rupture directivity is found in the eastward direction. Here, we explore the reasons for this apparent inconsistency by performing a joint source inversion of seismic and geodetic datasets, and conducting ground motion simulations. The results indicate that the earthquake occurred on the underthrusting Indian lithosphere, with a low dip angle, and that the fault rupture propagated in the along-strike direction at a velocity just slightly below the S-wave velocity. This low dip angle and fast rupture velocity produced rupture directivity in the along-strike direction, which caused widespread ground motion distribution and significant damage extending far eastwards, from central Nepal to Mount Everest.
authors.affiliation: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, Japan.
authors.forename: Kazuki
authors.initials: K
authors.lastname: Koketsu
authors.affiliation: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, Japan.
authors.forename: Hiroe
authors.initials: H
authors.lastname: Miyake
authors.affiliation: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, Japan.
authors.forename: Yujia
authors.initials: Y
authors.lastname: Guo
authors.affiliation: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Kobayashi
authors.affiliation: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, Japan.
authors.forename: Tetsu
authors.initials: T
authors.lastname: Masuda
authors.affiliation: National Geophysical Research Institute, Uppal Road, Hyderabad, India.
authors.forename: Srinagesh
authors.initials: S
authors.lastname: Davuluri
authors.affiliation: Department of Mines and Geology, Lainchour, Kathmandu, Nepal.
authors.forename: Mukunda
authors.initials: M
authors.lastname: Bhattarai
authors.affiliation: Department of Mines and Geology, Lainchour, Kathmandu, Nepal.
authors.forename: Lok Bijaya
authors.initials: LB
authors.lastname: Adhikari
authors.affiliation: Department of Mines and Geology, Lainchour, Kathmandu, Nepal.
authors.forename: Soma Nath
authors.initials: SN
authors.lastname: Sapkota