Japan Geoscience Union Meeting 2021

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[E] Oral

S (Solid Earth Sciences ) » S-CG Complex & General

[S-CG40] Active Tectonics and Seismic Hazards in the Himalayan Region

Sun. Jun 6, 2021 1:45 PM - 3:15 PM Ch.24 (Zoom Room 24)

convener:Kazuki Koketsu(Earthquake Research Institute, University of Tokyo), Nath Soma Sapkota(Nepal Geological Society), Srinagesh Davuluri(CSIR-National Geophysical Research Institute), Chairperson:Kazuki Koketsu(Earthquake Research Institute, University of Tokyo), Hiroe Miyake(Earthquake Research Institute, University of Tokyo)

2:45 PM - 3:00 PM

[SCG40-05] Rupture History of the Himalayan Frontal Thrust near Bagmati River crossing in Central Nepal

*Koji Okumura1, Prakash Pokhrel3, Hisao Kondo2, Tomoru Yamanaka1, Soma Nath Sapkota3 (1.Graduate School of Letters, Hiroshima University, 2.Research Institute of Earthquake and Volcano Geology, GSJ, AIST, 3.Department of Mines and Geology, Nepal)

Keywords:Himalayan Frontal Thrust, paleoseismology, surface rupture

The 2015 Golkha earthquake raised concern about the future large earthquake occurring in south of the 2015 source area. The 2015 earthquake ruptured 10 to 20 km deep portion of the plate boundary interface ~50 km away from the surface trace of the frontal thrust. It is necessary to evaluate the earthquake potential of the shallowest part of the Himalayan Frontal Thrust in central Nepal. After 5 years of intensive studies on the rupture history, now there are important questions about three large past earthquakes of 1934, 1344, and 1255 (or 13 century). They are, (1) the existence and extent of 1934 surface rupture, (2) the existence and extent of 1344 rupture, and (3) the extent and exact timing of 1255 (or 13th century) event. As to the 1934 surface rupture, Rizza et al. (2019) as well as Sapkota et al. (2012) demonstrated ruptures on fault exposures against Wesnousky et al. (2018) in Bardibas area. However, the west terminations of the 1255 and 1934 rupture have not been defined yet. We excavated two trenches on the Himalayan front in east and in west of Bagmati river to examine the terminations and to know the rupture history. At the Dumachaur Khola site 4 km east of Bagmati river, 3 or 4 events in 3500 years are excavated. The timing of the last event here is in the earlier half of the 2nd millennium C.E.. At the Gopalkoti-Dandatol site, 0.7 km west of Bagmati river, 2 or 3 events between 3rd and 14th century C.E. are recognized. 1934 ruptures do not appear in both trenches. This study is a part of the JICA-JST SATREPS project: Integrated Research on Great Earthquakes and Disaster Mitigation in Nepal Himalaya.