This study estimates the source, propagation path, and site amplification factors of the two regions in the Philippines: the Luzon and Mindanao. Using the generalized spectral inversion technique, we separated the acceleration Fourier spectra of the ground motions recorded by the Philippine Seismic Network (PSN) from 2016-2020. The source, site amplification, and anelastic attenuation (Q) factors in the two regions were estimated using the "reference event" and the "reference site" constraints. We obtained almost similar results in the Q factor using the two constraints. The "reference site" approach shows stable results in the Mindanao region. However, when using the "reference event" approach, each site's estimated site amplification factors show spectral decay in the high frequencies for the Mindanao region. The same spectral decay in the Luzon region using the "reference site" constraint. The obtained source spectra also differ among the two constraints, especially in the Mindanao region. We found that the spectral amplitudes in the higher frequencies possibly depend on the earthquake's source depth, not their source type. In the Luzon region, spectral amplitudes in the higher frequencies are observed for crustal earthquakes when we adopt the "reference site" constraint. The Q-values in the Luzon region using the reference site approach shows a weaker frequency-dependent than those estimated in the Mindanao region.
Keywords: Seismic wave attenuation, Site amplification factor, Source factor, Spectral inversion