The influence of earthquake source complexity on frequency-dependent radiation patterns by modifying distance-dependent properties

The double-couple model of the earthquake source has been proven remarkably successful in explaining the radiation pattern in the low-frequency wavefield. However, the radiation pattern is distorted in the high-frequency wavefield. The frequency dependence of the radiation pattern is often interpreted as the path effects. The impact of earthquake sources on radiation patterns is uncertain. In our study, based on the fact that P waves vibrate along the radial direction and S waves vibrate along the transverse direction, the path effects modified model of radiation pattern is proposed based on the optimal ratio coefficient by measuring radial-to-transverse spectral ratios at multiple frequency ranges. Then, we found that the correlation coefficient decreases with the increase of frequency but remains stable with the increase of distance. This means the complexity of the earthquake source can distort the wavefield at higher frequencies and drive variability in the ground motion.