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Abstract:
Upon entering a medium with a strongly anisotropic feature, shear-waves refract and produce two orthogonally polarized waves, travelling with different velocities (the Sfast and Sslow). The polarization direction of the Sfast and the time-delay between the arrivals of the two waves are common metrics to quantify splitting. In the upper crust, anisotropy has been often attributed to stress-sensitive fluid-filled microcracks, whose characteristics may change over time. The Habanero Geothermal Field in Cooper Basin (Australia) is a site of multiple hydraulic stimulation tests, closely monitored by a dense network of 24 surficial and borehole sensors. In the current study, we use a fully automatic analysis scheme to identify shear-wave splitting in waveforms of approximately local 30,000 earthquakes, which occurred in a shallow ~500 m thick sub-horizontal layer. Results indicate a complex state of anisotropy, with both azimuths of faulting and the local maximum horizontal compressive stress component being represented in the measured polarization directions. Time-delay changes present a potential association with the activation of the structure due to the stimulation.
Acknowledgements
The research project was supported by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the “2nd Call for H.F.R.I. Research Projects to support Post-Doctoral Researchers” (Project Number: 00256).
