Full-Waveform Reconstruction of Microseismic Sources From Hydroacoustic Observations

This work presents a full-waveform reconstruction strategy to identify microseismic events in solid–fluid systems using multi-frequency acoustic pressure measurements collected in the fluid. The goal is to recover both the locations and seismic moment tensors of the events, motivated by applications such as monitoring reaction-induced fracturing in subsurface carbon storage formations. Microseismic sources are modeled as dipole and double-couple point forces embedded in the solid domain. The reconstruction is carried out via a topological derivative approach, in which the leading-order perturbation of a misfit functional is driven by the elastic energy released through the creation of an infinitesimal fracture at a trial location. The forward problem is formulated in the frequency domain, coupling elastodynamics in the solid and acoustics in the fluid. The inversion algorithm combines a discrete grid search, adaptive refinement strategies, and multi-frequency data assimilation. Numerical simulations in two dimensions demonstrate the ability to reconstruct multiple sources using a modest number of hydrophones. The results also highlight the interplay between spatial and spectral aperture, showing that limitations in one can, to a degree, be compensated by abundance in the other.