Intensity of Nepal-Sikkim 6.8 Earthquake

Intensity Mapping in Eastern towns of Nepal

Prithvi Shrestha and Chintan Timsina

This is a report of field trip for the Intensity Mapping of some major towns in Northeast part of Nepal due to recent Taplejung-Sikkim earthquake of magnitude 6.8 occurred in Sept. 2011 in the evening. The location of the quake was latitude 27.71N and longitude 88.30E with shallow depth about 20 km. Strong shaking was felt in the capital city Kathmandu too 300 km far from the epicentre. This earthquake is intraplate earthquake and occurred in the higher mountain range. Observation was done in the following towns along with questionnaire and photographs, which are included.

1) Phungling Bazaar: - It is a centre town of Taplejung district about 70 km southwest from epicentre.  Few damage found in the centre although strong shaking felt by the people. Three houses are found to be damage outside of the town among them two are heavily damage. Many houses damage and landslides are reported in the remote side near to the epicentre. Talking to the local people it is expected that the intensity should be between V to VII in MMI scale.

2) Phidim Bazaar: - Also 70 km far from epicentre, Phidim Bazaar too felt the strong shaking. In the town three houses are fully damaged and several houses are cracked. Landslides on the way in some places are also observed. Here also many houses damage and landslides are reported in the remote village areas. By interaction with the people and questionnaire they filled suggest that intensity should be between V to VII. 

3) Ilam Bazaar:- Although shaking was strong but less damage are found here. This town is 95 km far from epicentre. We observed few houses with hair crack. On the way near Puwa river 5 meters rupture was seen. Little far from the town we observed weak plaster fallen in some adobe type houses. But still many houses and landslides are reported from remote areas. On the basis of filled questionnaire by the people here, the intensity should vary from IV to VI.

By interaction and questionnaire with the local people, we came to know that heavy damage was occurred in the villages where very old houses made of adobe and wood-mortar are likely to find. Landslides were also observed in some places on the way. Due to difficulty in accessing the road, heavy rain and less time our team was unable to reach to the earthquake affected remote areas, so less information from those areas.

The aim of the mission was not only to map intensity but also to install new GPS, Accelerometer and Broadband Seismic Stations and download GPS data. GPS stations are deployed in Tumlingtar, Ilam and Jhapa whereas Broadband seismic stations are deployed in Dhankuta, Jhapa, Ilam and Taplejung. In Taplejung, Tumlingtar and Ilam an Accelerometer are installed. Due to lack of time, inconvenient road access and remoteness of the affected area we lack the information of damage parameters. Although the intensity distribution seem to be between IV to VII in MMI but it is not justifiable to estimate intensity only on the basis of observation in the towns. It is reported that this earthquake heavily affected Sikkim side too. So it is better to wait for more information from both, Sikkim and our remote side to estimate the final intensity map.