Low-Frequency Resonance in Strong Heterogeneity

Abstract

Multiple scattering of wave in strong heterogeneity can cause resonance-like wave anomaly where the signal exhibits low-frequency, high intensity, and slowly propagating wave packet velocity. For example, long period event in volcanic seismology and plasma oscillations in wave-particle interactions. Collective behaviour in a many-body system is thought to be the source for generating the anomaly, however the detailed mechanism is not fully understood. Here I show that the physical mechanism is associated with low-frequency resonance (LFR) in strong small-scale heterogeneity through seismic wave field modeling for bubble cloud heterogeneity and 1D heterogeneity. LFR is a kind of wave coherent scattering enhancement or emergence phenomenon that occurs in transient regime. Its resonance frequency decreases with increasing heterogeneous scale, impedance contrast, or random heterogeneous scale and velocity fluctuations; its intensity diminishes with decreasing impedance contrast or increasing random heterogeneous scale and velocity fluctuations. LRF exhibits the characteristics of localized wave in space and the shape of ocean wave in time and is a ubiquitous wave phenomenon in wave physics. The concept of LFR can open up new opportunities in many aspects of science and engineering.