198 Geophysics in Geothermal Exploration Among those two parameters, the so-called b-value is critical and defines the slope of the straight line that characterize the relationship (Pérez and Cuellar, 2018). The b-value is considered an indication of the type of process that drives the seismic mechanisms, with values close to 1 associated with tectonic process, considering a homogeneous crust submitted to high stress field, whereas b-values greater than 1, sometimes close to 2, are representative of geothermal and volcanic environments. Multiple reasons are invoked to explain this difference, such as heterogeneity, low effective stress, fracturing, high thermal gradient, change of fluid composition and distribution, we refer the reader to Pérez and Cuellar (2018) to access multiple references on that topic. As an illustration of the method, shows the results of a pseudo 3D tomography of b-values conducted by Benton et al. (2011) at the geothermal field of Tres Virgenes in Mexico. Several high b-values anomalies are identified that seem correlated to different known faults in the area that exhibit high fracturing degree and intense hydrothermal fluid circulation (Antayhua-Vera et al., 2022). Figure 6.8 Modified after Antayhua-Vera et al. (2022). Results of a pseudo-3D tomography of b-values conducted at the Tres Virgenes geothermal field. Waveform analysis Following a similar logic as for b-values analysis, geothermal or volcanic contexts tend to induce seismic events whose waveform might differ from events produced in “pure” tectonic context. Waveform analysis, in the temporal of frequency domain can be a way to distinguish both environments, hence better characterizing
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