3:00 PM - 3:15 PM
[SCG40-06] Strong Motion Observation Network for Earthquake Disaster Mitigation in the Kathmandu Valley, Nepal
Keywords:Strong Motion Observation Network, Nepal Himalaya, Kathmandu Valley
The Himalayan continental collision zone of the Indian plate and the Eurasian plate have been causing many devastating earthquakes in the past. The Kathmandu Valley in Nepal is filled with soft soil of Plio-Pleistocene origin the thickness of the sediments is more than 600 m in the central part of the valley. Because of the site amplification of this sediment structure, many damages occurred not only by the near earthquakes (e.g., the 2015 Gorkha Nepal earthquake) but also by the far earthquakes (e.g., the 1934 Bihar-Nepal, the 2011 Taplejung-Sikkim earthquakes).
Moreover, the residential area in the Kathmandu Valley has been spread quickly in recent years by the explosive population growth. By this seismological and social environment, the earthquake damage risk of this metropolitan area in the valley is increasing. This risk must be reduced by a high precision prediction for the next great earthquake which has the potential to occur in the Central Seismic Gap of the Main Frontal Thrust in Nepal Himalaya.
There were six known seismic observation sites in the valley: one station by USGS, one station by the Department of Mines and Geology, Ministry of Industry, Commerce, and Supplies and four stations by the collaborative observation of Hokkaido University and Tribhuvan University (Takai et al., 2016). However, the density of these former stations was too low to know the site amplification variation in the valley whose diameter is about 25 km in detail.
“Integrated Research on Great Earthquake and Disaster Mitigation in Nepal Himalaya” is a project of the Science and Technology Research Partnership for Sustainable Development program supported by JST and JICA (SATREPS NERDiM, 2016-2021, Principal Investigator: Kazuki Koketsu). By this NERDiM project, in order to accumulate the strong motion data, the strong motion observation network was installed with ten strong-ground motion seismometers in Nov. 2016- May 2018. There was only one rock site station (Kirtipur) in the valley, therefore, we installed the instruments to north, west, and east rock site stations. Moreover, we selected the heavily damaged area (Balaju) during the 2015 Gorkha Nepal earthquake and the low-density observation area as observation sites.
Even the small amount of accumulated important data can show the difference of the amplification factor at each station in the valley. The north rock site Jhor and the east rock site Sanga have predominant periods in 0.25 - 0.3 s, on the other hand, other sedimentary sites have those in 1.2 - 5 s (2018 JpGU, 2019 SSJ). We have constructed the 1-D and 3-D deep sedimentary velocity structure models in the Kathmandu Valley (Bijukchhen et al., 2017, Bijukchhen, 2018) by using aftershock records of the 2015 Gorkha earthquake of existing stations. After installing these observation sites, we could compare the observed receiver function with the theoretical one (2020 JpGU, 2020 WCEE). In this comparison, the observed receiver functions agreed with the theoretical ones in most stations except stations on the center and marginal part of the valley, which is not used by the construction of that velocity model. Also, we made the correction term of the ground motion prediction equation (GMPE) for velocity response spectra for this valley using aftershock records and depth to seismic bedrock of the valley (2020 SDEE). This will be a powerful tool for making the design spectrum for a long period of ground motion for high-rise buildings increasing in the valley.
The accumulation of the strong motion data by this new network will be able to upgrade this GMPE and the underground structure to contribute to the disaster mitigation planning for the Kathmandu metropolitan area, in the future.
Acknowledgments: A part of this research was supported by SATREPS of JST-JICA Grant Number JPMJSA1511, and JSPS KAKENHI.
Moreover, the residential area in the Kathmandu Valley has been spread quickly in recent years by the explosive population growth. By this seismological and social environment, the earthquake damage risk of this metropolitan area in the valley is increasing. This risk must be reduced by a high precision prediction for the next great earthquake which has the potential to occur in the Central Seismic Gap of the Main Frontal Thrust in Nepal Himalaya.
There were six known seismic observation sites in the valley: one station by USGS, one station by the Department of Mines and Geology, Ministry of Industry, Commerce, and Supplies and four stations by the collaborative observation of Hokkaido University and Tribhuvan University (Takai et al., 2016). However, the density of these former stations was too low to know the site amplification variation in the valley whose diameter is about 25 km in detail.
“Integrated Research on Great Earthquake and Disaster Mitigation in Nepal Himalaya” is a project of the Science and Technology Research Partnership for Sustainable Development program supported by JST and JICA (SATREPS NERDiM, 2016-2021, Principal Investigator: Kazuki Koketsu). By this NERDiM project, in order to accumulate the strong motion data, the strong motion observation network was installed with ten strong-ground motion seismometers in Nov. 2016- May 2018. There was only one rock site station (Kirtipur) in the valley, therefore, we installed the instruments to north, west, and east rock site stations. Moreover, we selected the heavily damaged area (Balaju) during the 2015 Gorkha Nepal earthquake and the low-density observation area as observation sites.
Even the small amount of accumulated important data can show the difference of the amplification factor at each station in the valley. The north rock site Jhor and the east rock site Sanga have predominant periods in 0.25 - 0.3 s, on the other hand, other sedimentary sites have those in 1.2 - 5 s (2018 JpGU, 2019 SSJ). We have constructed the 1-D and 3-D deep sedimentary velocity structure models in the Kathmandu Valley (Bijukchhen et al., 2017, Bijukchhen, 2018) by using aftershock records of the 2015 Gorkha earthquake of existing stations. After installing these observation sites, we could compare the observed receiver function with the theoretical one (2020 JpGU, 2020 WCEE). In this comparison, the observed receiver functions agreed with the theoretical ones in most stations except stations on the center and marginal part of the valley, which is not used by the construction of that velocity model. Also, we made the correction term of the ground motion prediction equation (GMPE) for velocity response spectra for this valley using aftershock records and depth to seismic bedrock of the valley (2020 SDEE). This will be a powerful tool for making the design spectrum for a long period of ground motion for high-rise buildings increasing in the valley.
The accumulation of the strong motion data by this new network will be able to upgrade this GMPE and the underground structure to contribute to the disaster mitigation planning for the Kathmandu metropolitan area, in the future.
Acknowledgments: A part of this research was supported by SATREPS of JST-JICA Grant Number JPMJSA1511, and JSPS KAKENHI.