Assessment of earthquake-induced liquefaction hazard in urban areas of Hanoi city using LPI-based method

Abstract

Liquefaction Potential Index (LPI) is used as an assessing tool of liquefaction potential. In this stndy, the LPI­ based method was applied to evaluate the earthquake-induced liquefaction potential for the urban area of Hanoi city. The data used includes 120 boreholes logs, containing necessary geomechanical information such as fine contents, specific gravity, dry density, porosity, N (SPT) values and the groundwater depth Z(w) of subsoil layers in every borehole. The "simplified procedure" proposed by Seed and Idriss was applied to evaluate the liquefaction of all sub­soil layers in each borehole point. Then, the Liquefaction Potential Index was calculated for the whole soil column at all boreholes points using the method proposed by Iwasaki. Finally, the obtained LPI values were used to assess the liquefaction probability for an urban area of Hanoi city, using the empirical formula proposed by Papathanassiou and two earthquake scenarios originated on the Chay River fault with magnitndes of 5.3 and 6.5, respectively. For entire study area, the first scenario earthquake (Mw=5.3) is not capable of causing liquefaction (PG<0,1). This means that the downtown area of Hanoi city is non-liquefiable to the medium magnitude events. Results of the second scenario (Mw=6.5) show in worst cases, an earthquake with magnitude, maximum expected for Hanoi region can produce liquefaction throughout the downtown area of Hanoi city. The highest liquefaction probability of 0.7<PG≤0.9 is distributed in two large areas, where the first one is observed in Thanh Tri district, eastern part of Ha Dong, a smaller areas of the Thanh Xuan, Tu Liem and Cau Giay districts, while the second area covers Hoan Kiem district, a northern part of Hai Ba Trung district and northwestern part of Long Bien district. This is the first time the LPI based method was applied for evaluation of earthquake-induced liquefaction for Ha noi city. The most advantage of the method is that it can be easy to use, although the reliability of the results depends very much on number and distribution of the borehole data. Nevertheless, the combination of this method with other available methods can help effectively solving the problem of urban seismic risk assessment for the mega-cities in Vietnam.