Study on shaking intensity distribution of the 2015 Gorkha Earthquake in Nepal

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    Nepal was shaken by magnitude Mw7.8 Gorkha Earthquake on 25th April 2015 at 11:56 AM local time with the epicenter at Barpak, Gorkha, 80km North West of Kathmandu Valley. This Earthquake was followed by thousands of aftershocks including M6.6 and M6.7 within 24 hours and Mw 7.3 on 12th May 2015 which caused additional damage and casualties. According to official announcement, the impacts caused by this event included 8,969 people killed, and 22,321 injured in Nepal. In addition, significant damage to buildings, infrastructures and other critical services were well observed.

    There were very few strong motion instruments placed in different locations, especially in Kathmandu Valley before the earthquake, and data was recorded only in very few locations within Kathmandu Valley. So, only way to come up with comprehensive intensity distribution of the earthquake was through questionnaire survey.

    In this study, an attempt has been made to prepare the seismic intensity map of Gorkha Earthquake using the seismic intensity questionnaire survey. Study area was divided into several grids of different sizes 500*500m in highly dense area to some kilometers in low dense areas. The intensity survey summarizes the responses and average intensity was assigned to each grid. Questionnaire survey was conducted in key location starting from near to epicenter area to far away places where smaller shaking was observed. Through the survey at more than 300 locations in different parts of Nepal, intensity distribution map was developed. The intensity distribution shows that significant part of the affected area was suffered MMI VI to VII intensity, some area with MMI VIII and very few areas with intensity MMI IX. The results will be useful for earthquake risk assessment as well as planning for further earthquake risk management activities in Nepal.