Site-Specific Response Spectra: 2nd District of Cagayan de Oro City, Philippines

Abstract

Building codes are updated advertently to address the catastrophic effect of earthquakes. One way of mitigating it is the development of a site-specific response spectrum. In the Philippines, the National Structural Code of the Philippines (NPSC) is the recognized National Building Code adopting the 1997 Uniform Building Code (UBC). The NSCP uses the 10% probability of exceedance in a 50-year period with a return period of 475 years. In this study, site-specific response spectra were developed in the 2nd District of Cagayan de Oro City using a 300-km radius, with coordinates of 8.235° (latitude) and 124.024° (longitude) as the center point of the study area, using the same probability of exceedance in a 50-year period. Historical earthquake catalogs were gathered from the United States Geological Survey and the Department of Science and Technology – Philippine Institute of Volcanology and Seismology. Local soil condition was assimilated in the study to take into account the soil response. Finally, site-specific response spectra were developed using the probabilistic seismic hazard analysis where substantial results are achieved, i.e., the UBC 1997 design response spectrum is remarkably high in spectral acceleration values at 0.01, 0.20, 1.0, 2.0, 3.0, 4.0 and 5.0 s at 0.44, 1.1, 1.1, 0.7, 0.36, 0.26 and 0.20 g compared to the maximum site-specific response spectra of the study area of the same period at 0.39, 0.92, 0.23, 0.10, 0.07, 0.05 and 0.04 g spectral accelerations, respectively.