Rapid Estimation of Vs30 Through Elitist Genetic Algorithm Hvsr Inversion and Refraction Microtremor Data Analysis in Greater Metro Manila Area and Leyte Province, Philippines

Vs30, the average shear wave velocity in the uppermost 30 meters, is critical for seismic hazard analysis. In the Philippines, the Refraction Microtremor (ReMi) survey is one of the methods used to determine Vs30. This study investigates the use of an elitist Genetic Algorithm (GA) to invert Horizontal to Vertical Spectral Ratio (HVSR) data as a more efficient alternative. Unlike the ReMi survey, which requires laying out lines and geophones, the HVSR survey uses a single-unit, 3-component microtremor seismograph and can be operated by one person. Analyzing 174 HVSR and 52 ReMi datasets from the Greater Metro Manila Area (GMMA) and Leyte Province, we found that the estimated Vs30 estimates are satisfactory for site classes C, D, and E of the National Structural Code of the Philippines 2015 (NSCP 2015). The overall site class match rate is 76% in GMMA and 81% in Leyte. The R-squared values for measured Vs30 and estimated Vs30 comparisons for GMMA and Leyte are 0.885 and 0.806, respectively, indicating strong correlations. Additionally, the relationship between the fundamental site period and estimated Vs30 values was explored. The R-squared values range of 0.772 for GMMA and 0.707 for Leyte indicate a strong correlation and demonstrate the expected inversely proportion relationship between the two variables. Given the Philippines' high seismic activity, this approach could enable faster updates to seismic hazard maps, improving earthquake preparedness and mitigation.