Progress in Disaster Science (Apr 2021)
Seismic hazard assessment of the Kathmandu Valley and its adjoining region using a segment of the main Himalayan Thrust as a source
Abstract
An attempt has been made to evaluate seismic hazard in the Kathmandu Valley and its adjoining region. A segment of the Main Himalayan Thrust, which produced the 2015 Gorkha Earthquake is used as an earthquake source. Two rupture models of the source are utilized assigning unequal weight to estimate seismic hazard. The first model considers entire north-south rupture of the source that is similar to the rupture of the 1934 Bihar-Nepal Earthquake (Mw 8.2). The second model considers the northern-half rupture of the source, which is similar to that of the 2015 Gorkha Earthquake (Mw 7.8) and possibly the 1833 Nepal Earthquake (Mw 7.6).Seismic hazard maps are prepared for 500 and 200 year return periods at engineering rock site condition. A comparison is made between the peak ground acceleration (PGA) of Kathmandu and Nijgadh estimated for 200 year return period with the recorded PGA of the 2015 Gorkha Earthquake in Kathmandu (Kirtipur: a rock site) and empirically estimated PGA of that earthquake in Nijgadh respectively. Kathmandu and Nijgadh are selected for the comparison because Kathmandu falls within the rupture area of the 2015 Gorkha Earthquake and Nijgadh is in the Indogangetic Plain and away from the rupture area of that earthquake. The result shows that the PGA (0.23 g) estimated for Kathmandu for 200 year return period closely agrees with the instrumentally recorded PGA of the 2015 Gorkha Earthquake in Kathmandu (0.25 g). Instrumentally recorded PGA is not available in Nijgadh, which is at about 55 km in the south from Kathmandu. A seismic intensity survey was carried out in Nijgadh and its adjoining region to estimate the intensity of the 2015 Gorkha Earthquake in Nijgadh. The probabilistically estimated PGA (0.1 g) for Nijgadh for 200 year return period is in reasonable agreement with that of the 2015 Gorkha Earthquake (0.07 g) estimated from the seismic intensity (VI on MMI).
