Earthquakes

The entire territory of Nepal lies in high seismic hazard zone. The country's high seismicity is related to the movement of tectonic plates along the Himalayas that has caused several active faults. A total of 92 active faults have been mapped throughout the country by the Seismic Hazard Mapping and Risk Assessment for Nepal carried out as part of the Building Code Development Project – 1992-1994 (MHPP, 2994). Earthquakes of various magnitudes occur almost every year and have caused heavy losses of lives.

The entire country falls in a high earthquake intensity belt: almost the whole of Nepal falls in high intensity scale of MMI IX and X for the generally accepted recurrence period. The seismic zoning map of Nepal, which depicts the primary (shaking hazard), divides the country into three zones elongated in northwest-southeast direction; the middle part of the country is slightly higher than the northern and the southern parts.

The country has a long history of destructive earthquakes. In this century alone, over 11,000 people have lost their lives in four major earthquakes. A 1934 AD earthquake produced strong shaking in Kathmandu Valley, and destroyed 20 percent and damaged 40 percent of the valley’s building stock (NSET, 1999). In Kathmandu itself, one quarter of all homes was destroyed. Many of the temples in Bhaktapur were destroyed as well. This earthquake was not an isolated event. Three earthquakes of similar size occurred in Kathmandu Valley in the 19th Century: in 1810, 1833, and 1866 AD. The most recent earthquake that badly hit Nepal was the earthquake of 1988 which was a moderate size earthquake (Magnitude 6.5) affecting mostly the eastern part of Nepal. 721 people lost their lives in this earthquake.

Based on the data available from the Department of Mines and Geology, CBS (1998) concludes that earthquakes of more than or equal to 5.0 on the Richter scale have occurred at least once every year in Nepal since 1987, with the exception of 1989 and 1992 when no such events were recorded. The current disaster database of Nepal shows that there were 22 earthquakes with magnitudes ranging from 4.5 to 6.5 on the Richter scale throughout the country for last 37 years period (1971-2007). About 34,000 buildings were destroyed and 55,000 were damaged (DesInventar, 2007) during this period due to earthquakes. Many studies have been carried out in the past to evaluate the earthquake risk of Kathmandu Valley. The most significant among such studies are: the Study on Earthquake Disaster Mitigation for Kathmandu Valley conducted in 2002 by Ministry of Home Affairs (MoHA) with support from Japan International Coopertation Agency (JICA); and the earthquake risk assessment and scenario development in 1997 by Kathmandu Valley Earthquake Risk Management Project (KVERMP) implemented by the National Society for Earthquake Technology – Nepal (NSET). A simple loss estimation carried out during the KVERMP suggested that in case of a reoccurrence of similar shaking to that of 1934 in Kathmandu Valley would result in the following consequences: death: 40,000, injury: 95,000, homeless population: 600,000 – 900,000 , and building damage: 60% (NSET, 1999). Recent studies have shown that the situation is not much different in other cities also.

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