Characteristics of Higher-Mode Ambient Noise Rayleigh Waves in Taiwan: Insights from Multicomponent Interferometry

Abstract

This article reports on the characteristics of higher-mode Rayleigh waves retrieved from ambient noise collected by dense seismic networks in Taiwan. Through the multicomponent interferometry technique, we derived the empirical Green’s functions (EGFs) of Rayleigh waves. Both the fundamental mode and the first higher-mode Rayleigh waves were distinctly identified, and the effective energy of the EGFs falls within the frequency range of the short-period secondary microseism (SPSM, 0.2–0.5 Hz). To gain deeper insights into higher-mode Rayleigh waves, we conducted spatiotemporal analysis of the amplitude of the multicomponent cross-correlation functions, yielding the following key findings: (1) similar to the SPSM excitation, energy variations in both modes are closely correlated with shallow water environments, (2) higher-mode energy exhibits a strong correlation with underlying geological structures, with considerably stronger excitations detected in areas underlaid by soft sediments, and (3) temporal variations in the energy of both modes are strongly correlated with ocean wave height.