Spectral Anomalies in Microtremors Due to Subsurface Heterogeneities – 1D Numerical Simulations of Poroelastic Wave Propa

Abstract

We perform 1D numerical simulations of wave propagation in elastic and poroelastic media to investigate the Fourier spectra of the surface velocity-time signal for different material heterogeneities within the subsurface. The motivation of this study is to better understand the resonance effects in the low frequency band of observed ‘hydrocarbon tremors’. We use two systems of equations describing wave propagation in poroelastic media: one system based on the Biot theory and a second system based on the theory of porous media (TPM). The characteristic maxima in the Fourier spectra for low velocity surface layers, low velocity subsurface layers and attenuating subsurface layers can be predicted with analytical solutions for the standing wave resonance frequencies. Reflections from fluid-saturated layers generate Fourier spectra with amplitudes that depend on the layer thickness.