Surface Wave Anisotropy in Fractured Media: Insights from Wavefield Modelling and Applications for Geothermal Exploration

Characterizing faults in geothermal fields is essential for the energy transition, as faults enable efficient heat flow throughout the reservoir. Three-component (3C) beamforming, an ambient seismic noise technique, is a cheap and effective way to analyse fault-related anisotropy by observing surface wave velocities. 3C beamforming extracts the wave type, direction and phase velocities of coherent waves as a function of frequency, which provides an understanding of surface wave velocities. Anisotropic velocities have been shown to be caused by the presence of faults, giving an indication of the maximum depth of permeability within a geothermal reservoir. However, the relationship between faults and surface wave velocities must be examined in more detail. Wavefield modelling using a numerical model was done by propagating a wave through a model of the subsurface with anisotropy applied in the form of a fault at assumed directions. 3C beamforming was then used to analyse this synthetic data, providing information on an identifiable Rayleigh wave and how the velocity of the wave changes depending on fault azimuth. Therefore, indicating the effectiveness of ambient noise methods, like 3C beamforming, compared to that of far more expensive active seismic techniques; the development of which is crucial for the energy transition.