SITE CLASSIFICATION PRACTICE IN SHALLOW BEDROCK REGIONS IN ASIA: COMPARISON OF RESPONSE SPECTRUM

摘要

Seismic site classifications are becoming very popular in Asia because of seismic microzonation studies. Seismic site classifications are used to represent seismic site effects and estimate the hazard parameters at soil surface. Most countries including Australia, China and India follow seismic site classification system similar to that in International Building Code (IBC), which is based on 30 m average shear wave velocity (SWV), Standard Penetration Test (SPT) N values and undrained shear strength (Anbazhagan et al, 2010). This simulates actual site amplification fairly accurately for cases wherein bedrock depth is near about 30m, but when bedrock depth is varying too much on shallow or deeper side, such classification is bound to render erroneous results. In the present study, focus is on developing and comparing response spectrum according to 30m classification and site response study considering earthquake in the study area with different depth of soil profiles. Soil profiles with SPT N and SWV are obtained from Anbazhagan et al. (2010). These sites are classified and response spectrum has been arrived according to site classification systems' recommendations in IBC, NEHRP and codes of India, Australia and China. Site response parameters of these sites are estimated by carrying out site specific response studies using SHAKE and earthquake reported in these regions. In the conclusion, comparison of responses obtained is made and a new site classification is proposed on basis of varying bedrock depth.