Mapping and characterization of the liquefaction impacts of the July and October 2022 earthquakes in Northwestern Luzon, Philippines

Abstract

The 25 July 2022 MW 7.0 and 25 October 2022 MW 6.4 earthquakes caused liquefaction in the lowlands of Northwestern Luzon, Philippines. With the widespread liquefaction occurrence, a methodology was developed for mapping and assessing its impacts, which combined mapping techniques, geomorphological analysis, review of historical liquefaction accounts and empirical equations, utilization of available remote sensing technologies, and application of various geophysical and geotechnical equipment. The majority of liquefaction impacts of the MW 7.0 earthquake occurred along the Abra River delta, while the MW 6.4 earthquake had most of its liquefaction impacts concentrated in river dikes and abandoned channels across the Solsona Basin. Grain size analysis confirmed that the sediments indeed had the potential to liquefy. The soil parameters obtained using the refraction microtremor (ReMi) and screw driving sounding (SDS) tests also showed strong correlations, with liquefaction potential values ranging from low to high. Soil period values were also consistent with the ReMi and SDS results.The results of this study emphasize that: 1) detailed mapping and assessment of areas affected by liquefaction is valuable in aiding researchers and planners in hazard mitigation; and 2) the geophysical and geotechnical approaches employed are suitable and less invasive alternatives in site-specific liquefaction potential assessment.