An attempt has been made to evaluate seismic hazard in the Kathmandu Valley and its adjoining region. A segment of the Main Himalayan Thrust, whose partial rupture produced the 2015 Gorkha Earthquake is used as an earthquake source.
Two rupture models of the earthquake source are utilized assigning unequal weight to estimate seismic hazard for engineering rock site conditions. The first model considers entire north-south rupture of the source that is similar to that of the 1934 Bihar-Nepal Earthquake (Mw 8.2). The second model considers the northern-half rupture of the source, which is similar to the rupture area 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 of probabilistically estimated peak ground acceleration (PGA) is made with the recorded (PGA) of the 2015 Gorkha Earthquake recorded in Kirtipur (a rock site) in Kathmandu and its empirically estimated PGA in Nijgadh.
The result shows that, the probabilistically estimated PGA corresponding to 200 year return period, agrees with the PGA of the 2015 Gorkha Earthquake recorded in Kathmandu. Ground motion (PGA) record is not available in Nijgadh, which is in the south of Kathmandu Valley and in the south of the Main Frontal Thrust; therefore an alternative approach is adopted to estimate PGA in Nijgadh. Human perception was utilized to empirically estimate the PGA of the 2015 Gorkha Earthquake in Nijgadh . The empirically estimated PGA (0.07 g) in Nijgadh approximately agrees with probabilistically estimated PGA (0.1 g) for 200 year return period.