Liquefaction Hazard Scenario of Imphal City for 1869 Cachar and a Hypothetical Earthquake

Liquefaction Hazard Scenario of Imphal City for 1869 Cachar and a Hypothetical Earthquake

Kumar Pallav, S. T. G. Raghukanth, Konjengbam Darunkumar Singh
Copyright: © 2012 |Pages: 23
DOI: 10.4018/jgee.2012010103
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In the present article liquefaction potential of Imphal city is reported in the form of two indices, i.e., LPI (Liquefaction Potential Index) and LSI (Liquefaction Severity Index), for 1869 Cachar earthquake (Mw 7.5) along the Kopili fault and probable future great earthquake (Mw 8.1) in the Indo-Burma subduction zone. The Factor of Safety (FS) against liquefaction has been computed by using modified procedure given by Idriss and Boulanger (2006) for all depths of 122 boreholes. The computed FS have been used as input parameters for evaluating LPI and LSI indices for Imphal City. Based on these LPI and LSI indices, liquefaction potential hazard contour maps of Imphal city is prepared. It is observed that over a large area of Imphal city is highly vulnerable to liquefaction failure in the events of the selected earthquake. The liquefaction hazard obtained at each site exhibits a good agreement with the damages documented for 1869 Cachar earthquake. This contour map can be served as a guideline for engineer and planner in site selection for upcoming projects and helps city administration in mitigating the city from future hazards.
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1. Introduction

Imphal city (24.8ºN 93.9ºE), the capital of Manipur state, is situated at the extreme end of Northeastern (NE) India and adjacent to Myanmar. Past earthquake histories of NE India show that the region is seismically most active as compared to other parts of India. As a result, the NE region has been assigned Zone V (most severe seismic hazard zone) in the seismic zoning map of India (Bureau of Indian Standard, 2002). Liquefaction is a common cause of ground failure and structural damage in any earthquake (e.g., Kramer, 2008; Nandy, 2001; Madabushi & Heigh, 2005) viz., NE-India (1869, 1897, and 1950 Assam), Alaska (1964), Nigata (1964), Kobe (1985), Loma Prieta (1989), Turkey (1999) Adana-ceyhan (1999) Kocali, Taiwan (1999 Chi-Chi) and India (2001 Bhuj). In all these cities partial or complete bearing failures of shallow-founded structures occurred at sites due to liquefaction-type damages. Ambraseys (1988) studied worldwide earthquakes and liquefaction data and concluded that an earthquake of magnitude as low as 5 can produce liquefaction. It may be noted that since 1897, this NE region has experienced more than 1500 earthquakes of magnitudes ≥ 5. In seismic prone areas like Imphal city liquefaction potential must be evaluated during site selection and planning stages of engineering structures. In order to compute the liquefaction potential of soil, many methods have been developed by engineers and researchers (Seed & Idriss, 1971; Iwasaki et al., 1982; Seed & Idriss, 1982; Liao et al., 1988; Bartlett & Youd, 1995; Harder, 1997; Youd & Idriss, 1997; Youd & Noble, 1997; Chen & Juang, 2000; Cetin et al., 2002; Juang et al., 2003; Sonmez, 2003; Lee et al., 2003; Sonmez & Gokceoglu, 2005; Idriss & Boulanger, 2006; Moss et al., 2006).

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