Fig. 4: Source spectra and their ratios for the earthquake doublet.
a Upper panel: Source spectra from all stations (thin lines), along with the averaged spectra (bold lines) for the first (red) and second (blue) events. Lower panel: Ratio of the source spectra between the earthquake doublet (black) and the average ratio of the observed P-wave spectra (gray). The corner frequencies of the two source spectra are labeled by red and blue dashed lines, respectively. b A sketch diagram illustrating the theoretical source spectrum models. Upper panel: Lines in green and blue are source spectra (S0(f) and S2(f)) with the same decay exponent. Red lines denote the one (S1(f)) with a lower decay exponent, explained as the superposition of the source spectra of small asperities with variable corner frequencies. Lower panel: Ratios of the spectra shown in the upper panel.
