Preliminary study for evaluation of earthquake risk to the historical structures in kathmandu valley ( nepal )

In this study, an attempt to assess the seismic vulnerability of the historical infrastructures like temples and stupas of Kathmandu valley, Nepal was carried out. The estimation of periods of multi-tiered temples was done by using empirical equations. To estimate the periods of soil, theoretical transfer function of SH waves was used. It is found that there may not be severe impact to the temples located at the valley floor during far field earthquakes due to difference in predominant period of temples, stupas and the ground. However, temples and stupas which have experienced some past earthquake motions could exhibit longer natural period due to existing cracks. In such cases, there are possibilities of resonance effect because the period of temples and stupas are closer to the predominant period of the ground. Likewise, the temples located at the border of the Kathmandu Valley may have severe damage from resonance effect due to the short periods of temples and sites near rock outcrops. It is observed that most of the important temples like Pashupatinath, Nyatpol, Gujeshwori, Krishna Mandir, Banglamukhi and stupa like Boudhnath are situated over geological formations which may be at risk of liquefaction under sever seismic impact. These results are from the preliminary phase of analysis, and detailed field measurements such as the periods of structures, soil and various sub-surface structures are necessary for the further investigation.