Liquefaction studies for seismic microzonation of Delhi region

After the devastating 2001 Bhuj earthquake, the national capital region of Delhi has attracted major attention with several scientific studies in recent times. This region, being in zone-IV, has experienced many earthquakes in the past and recent times. It also faces the danger of severe seismic threat from the central Himalayan seismic gap. Seismic microzonation, which is a subdivision of an area into micro zones depending upon site-specific seismic response, is an effective mitigation method. During an earthquake, soil can fail due to liquefaction with devastating effects such as land sliding, lateral spreading, or large ground settlement. The phenomenon of liquefaction of soil had been observed for many years, but was brought to the attention of engineers after the Niigata (1964) and Alaska (1964) earthquakes. Since Delhi falls in the area with high seismic probability, there is need for the assessment of liquefaction potential. An extensive geotechnical borehole database has been prepared after compiling more than 1200 boreholes at various locations of Delhi, along with geological and seismological details. In this article, with the collected borehole data an attempt is made to assess in detail the liquefaction potential of soils using SPT-based methods and also to present a liquefaction hazard map.