Holistic Overview of the Contribution of Tectonic, Geomorphic, and Geologic Factors to the Seismic Hazard of the Kathmandu Valley, Nepal
Abstract
Nepal has been a seismically active region since the mid-Eocene collision of the Indian and Eurasian plates. It can be divided into four major tectonostratigraphic units. The Lesser Himalayan Zone, where Kathmandu Valley is located, is bounded to the south by the Main Boundary Thrust (MBT) and to the north by the Main Central Thrust (MCT). These faults, and the Main Frontal Thrust (MFT) traverse the NW-SE length of Nepal and sole into the Main Himalayan Thrust (MHT). Slip along these structures during the Plio-Quaternary has ponded sediment in the interior of the orogen, producing the nearly circular Kathmandu Basin, which hosts a series of radially converging rivers that exit the basin to the south. The sediment that is ponded within the basin consists of alluvial, lacustrine and debris flow deposits that are ~500 m thick. The faults in the vicinity of the Kathmandu Valley currently serve as potential earthquake sources. Sources that might plausibly be generated by these faults are constrained by structural, paleoseismic, and geodetic observations. The continued collision between India and Tibet is reflected in a convergence rate of about 20 mm/yr, as measured by Global Positioning System (GPS) geodetic networks. Strain accumulates on the MHT, and is released during large earthquakes. The epicenter of the 1934 (M8.2) earthquake, about 175 km to the east of Kathmandu, resulted in MMI VIII- IX shaking intensity in the Kathmandu Valley. Seismic waves generated from faults in proximity to Kathmandu may be amplified or attenuated at particular locations due to specific site responses that reflect the geologic framework of the Kathmandu Valley. The ponded sediments within the Kathmandu Basin may contribute to basin effects, trapping seismic waves and prolonging ground motion, as well as increasing the amplitude of the waves as they travel from crystalline outer rocks into the soft lake-bed sediments. A hazard analysis suggests that a M8.0 earthquake originating in the currently seismically-locked area to the west of Kathmandu would produce MMI VIII intensity in Kathmandu Valley, and a M5.8 earthquake on an active fault in the valley itself would result in MMI IX intensity close to the fault, and MMI VII - VIII elsewhere in the valley. The government of Nepal initiated a seismic hazard analysis and scenario-based estimation of the impact of a major earthquake in Kathmandu Valley in support of the development of a National Building Code. Earthquake awareness, preparation and mitigation initiatives have been undertaken, including implementation of the School Earthquake Safety Program, a preparedness and risk mitigation program for raising awareness and strengthening vulnerable buildings. The effectiveness of this program has been well-demonstrated, and it is a candidate for acceleration of adoption.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMED41A0731B
- Keywords:
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- 4334 NATURAL HAZARDS Disaster risk communication;
- 4302 NATURAL HAZARDS Geological