SEISMIC MICROZONATION OF DELHI

Abstract

India is among the countries, which are more vulnerable to a variety of natural disasters. Perhaps, floods, droughts and cyclones are managed in a more professional manner, due to their relatively high frequency of occurrence. As far as earthquakes are concerned, the level of preparedness among engineers, administrators, and property owners need improvements. Risk of economic and human loss due to impending seismic hazard is increasing every year, since population of the country is getting agglomerated in the form of urban clusters and cities. Delhi, the capital of India falls in the seismic zone IV. ; Earthquakes of intensity up to IX and magnitude between 6-7 have occurred in the past in this region. After independence, there has been a tremendous growth in population and industrial activity in Delhi. I-Ience, even a magnitude 6 earthquake may cause widespread devastation. Thus, seismic Microzonation of mega cities like Delhi, situated in earthquake prone area becomes important, so that the planners can make use of it for better land use planning and safe development. In this present study microzonation of Delhi region has been proposed. After estimating the seismic hazard the seismic zonation map is prepared. The different tectonic features around Delhi region were identified and maximum credible earthquake at different features were proposed based on the seismicity data. (PGA) at bedrock level on a dense grid were computed using attenuation relation, considering all the tectonic features. The contours PGA values at the bedrock level revealed that the seismic zones may me more hazardous to Delhi city in future. In this work, geological and geotechnical data of Delhi region were collected and then parameters such as shear wave velocity, frequency dependent amplification factors, III predominant period of soil were computed. For this purpose a computer program in C' language was written. The average amplification factors in different frequency band were also computed. Peak ground accelerations at the surface were computed using PGA at bedrock level and the frequency dependent amplification factors at different locations. From the results obtained, contours of PGA values at the ground surface were plotted for dominant frequency as well for different frequency bands, thus paving the way for seismic Microzonation of Delhi. Analysis of these contours reveals that risk level is variable for different types of buildings at different localities. IV