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