Reliability-based seismic liquefaction hazard mapping of Kolkata Metropolitan City, India, using ordinary kriging technique

Soil liquefaction-induced damages in buildings and foundation during earthquakes increase the seismic hazard of densely populated urban cities dwelling on young alluvial soil deposits with a rising demand for infrastructural developments. Generally, liquefaction potential is evaluated for specific sites, which lacks the information related to the spatial extent of liquefaction effects. In the present study, liquefaction hazard maps of Kolkata metropolitan city is prepared for potential future earthquakes considering the spatial variability of soil parameters. The importance and application of geostatistical interpolation tools for hazard mapping are highlighted in this paper. Deterministic procedures of Boulanger and Idriss (2004, 2014) were utilized to quantify the liquefaction potential of two types of soil deposits, silty clay and silty sand, in the study area. Probability of liquefaction (P_L) was evaluated by first-order second moment (FOSM) reliability method for 2% and 10% probability of exceedance in 50 years. Python codes were developed for the calculation of factor of safety (FS) and P_L values for silty sand and silty clay. Spatial distribution maps in terms of FS and P_L were generated at 7 m, 15 m and 25 m depth of the study area using ordinary kriging technique in ArcGIS software. The regions of Maidan, Newtown, Rajarhat, Santoshpur, Sector V and Tangra were found to be vulnerable to liquefaction till 15 m depth. Additionally, correlations were also developed between P_L and FS using non-linear regression analysis for all soils, silty clay and silty sand of the study area for both the probabilistic scenarios.