A new approach to liquefaction hazard zonation: Application to Laoag City, Northern Philippines

To help mitigate liquefaction hazards in the Philippines, an inexpensive yet effective approach to liquefaction hazard zonation was developed in this study. The proposed approach is also useful in other areas especially where funds for more rigorous procedures may not be available. The approach utilizes the geomorphology-based criteria to identify liquefaction-prone deposits based on geology and grain characteristics, and generate a preliminary liquefaction susceptibility map. Then, microtremor recordings, popularly used in site effect estimation, are gathered to derive qualitative information on the density and thickness of these deposits and generate a site classification map. This latter map is also essentially a ground shaking hazard map in that it shows those areas where thick, soft deposits likely to amplify and prolong the duration of ground motion can be found. Therefore, it also identifies areas where seismic demand can be high that the possibility of liquefaction being triggered is likewise high. Combining the two maps, an integrated liquefaction hazard zonation map is produced which provides not only an improved characterization of the soils’ capacity to resist liquefaction but also integrates qualitative information on the seismic demand on these deposits as well. With information about the relative thickness of the deposits, the severity of potential damage can likewise be inferred from the map since thicker deposits relate to more serious damage. The proposed approach was applied to Laoag City, Northern Philippines, where it was shown to reliably identify areas that are vulnerable to the hazard.