[S-SS13] Strong Ground Motion and Earthquake Disaster

[SSS13-P32] Seismic reflection survey in the Kathmandu Valley, Nepal.

*Kota Koshika¹, Yusuke Kawasaki¹, Om Pradhan¹, Masato Yamamoto¹, Dai Nobuoka¹, Yoshikazu Matsubara¹, Hisanori Matsuyama¹, Monika Jha², Chintan Timisina², Suresh Shrestha², Mukunda Bhattarai², Dinesh Nepali², Soma Nath Sapkota², Hiroe Miyake³, Kazuki Koketsu³ (1.OYO Corporation, 2.Department of Mines and Geology, 3.Earthquake Research Institute, University of Tokyo)

Keywords:Kathmandu Valley, seismic reflection survey

On the April 25, 2015, earthquake of magnitude 7.8 Mw (USGS, 2015) struck in the 78 km north west of Kathmandu (Gorkha Earthquake) and major after shock of magnitude 7.3 Mw, with epicenter about 80 km north east of Kathmandu cases heavy damage in the Kathmandu Valley (KV). It was thought that the damage in the KV was particularly great, due to the underground structure of the KV.

We conducted gravity survey in the KV as part of the SATREPS projects in 2017. The shape of the gravity basement of the whole KV was estimated (Pradhan et al.,2018).

We conducted seismic reflection survey to clarify the detailed basement of the KV and the upper sedimentary structure in 2018. Survey lines were set up at Tribhuvan International Airport (TIA) where depth of gravity basement greatly changes and Nepal Agricultural Research Council (NARC) where deep gravity basement was estimated. Survey line length is about 4km (TIA) and 1km (NARC). Enviro Vibe (IVI, Inc.) was used as a seismic source.

The shape of the basement obtained by the seismic reflection survey and the shape of the gravity basement match well and the structure of the sedimentary layer in the basin was also revealed. These are the world's first results visually showing the underground structure in the KV and are expected to greatly contribute to future earthquake disaster prevention.