200 Geophysics in Geothermal Exploration anomalies are potentially related to a configuration of fluid bearing sediments associated with fracturing, such context suggesting favorable conditions for geothermal exploitation (Figure 6.9b). Figure 6.9 Modified after Muksin et al. (2013). Horizontal slices of the Vp and Vp/Vs 3D models at depth of 0, 2, and 6 km for Vp in (a), (b), and (c), and for Vp/ Vs in (d), (e), and (f). Vp/Vs ratio measurements designate the analysis of the velocity ratio of the P (compression) and S (shear) body waves. It allows a qualitative interpretation of the subsurface elastic properties, and has proven a useful approach in seismic geothermal exploration as Vp/Vs anomalic values have been able to identify different geothermal favorable contexts. For instance, as discussed, Muksin et al. (2013) identified fluid-bearing sediments through high Vp/Vs anomalies, whereas Simiyu (2009) identify and delineate the heat source of the Menengai caldeira in Kenya as a low Vp/Vs anomaly (Figure 6.10). In geothermal context, low Vp/Vs values are usually associated with a local decrease of P-wave velocity due to low pore pressure, high heat flow, fracture systems and vapor/gas saturation presence in the surveyed area (Pérez and Cuellar, 2018).
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