Microtremor and Earthquake Damage Survey in and around Kathmandu, Nepal
Takumi Hayashida, Senior Research Scientist
International Institute of Seismology and Earthquake Engineering
In response to the occurrence and severe damage of the April 25, 2015 Gorkha
Earthquake (Mw7.8) in Nepal, the Japan Science and Technology Agency (JST) started researchsupport funds “Japan-Nepal Urgent Collaborative Projects (J-RAPID Program)”. As a member of a
research project “Investigation of Ground-motion to Damage Relationship in the Kathmandu Valley
from Aftershock and Microtremor Observations (Principal investigators: Prof. Kazuki Koketsu at
the University of Tokyo and Dr. Soma Nath Sapkota, Deputy Director General at the Department ofMines and Geology, Ministry of Industry, Nepal)” under the J- RAPID program, I visited Nepal
from September 17 to 26 for field survey with Dr. Masumi Yamada, Prof. Jim Mori (Kyoto Univ.)and Dr. Walter D. Mooney (USGS). Our research team conducted single-point microtremor
observations*1 in the Kathmandu valley (city center and historical areas, including mainshockobservation sites) and surrounding damaged areas (e.g Chautara, Bahrabise, and Dunche), anddamaged school buildings (Sankhu area) using a portable microtremor observation system*2, toinvestigate the relationship between natural periods of ground and building damage. Theobservation period was seven days and it was a very short time for the survey in a wide range ofareas, but we could obtain microtremor data at more than 70 sites. Our observed data in theKathmandu valley show dominant peaks of microtremors in the long period range, indicating deep
sediment layers. Many local people were interested in our observations and provided us valuable
information such as damages caused by just after the mainshock. We also investigated theearthquake damage of buildings along with the microtremor observations in detail. Many low-risedbuildings were collapsed in the areas northwest – northeast of Kathmandu and the sights left animpression on me.
We also visited the National Society for Earthquake Technology (NSET) and the National
Seismological Centre, Department of Mines and Geology (NSC-DMG) and had a discussion onearthquake damage and research trends in some running international projects. In NSC-DMG, we
met ex-participants of IISEE training course [Mr. Mukunda Bhattarai (2004-2005 and 2013-2014
Seismology courses), Mr. Lok Bijaya Adhikari (2002-2003 Seismology course; 2013 Globalcourse), Mr. Umesh Prasad Gautam (2010 Global course)].
The detailed results of our damage and microtremor surveys were published in Earth, Planets andSpace (see https://earth-planets-space.springeropen.com/articles/10.1186/s40623-016-0483-4).

Pgoto 1: Kathmandu basin

Photo 2: Microtremor observation(at Patan Durbar Square)

Photo 3: Discussion at NSET

Photo 4: Discussion at NSC-DMG*1: The ground is always vibrating with very-small amplitude due to natural phenomena such as
ocean waves and wind, and human activities (we call the phenomena microtremor, ambient
vibration or seismic noise). The microtremor data have information about underground soil
structure and ground motion properties of the site.
*2: We used a portable microtremor observation system with three-component accelerometer
DATAMARK JU-310 (Hakusan corporation) for our microtremor observations. The sensor issometimes used for lectures of Regular (S and E) and Global courses. Dr. Hisatoshi Kahiwa at
the|National Institute for Land and Infrastructure Management provided us the instrument for thissurvey.