214 Geophysics in Geothermal Exploration Figure 6.19 Modified after Obermann et al. (2015). Decoherence time series measured for multiple seismic station pairs at the St Gallen geothermal field. (a) Pairs crossing the reservoir. (b) Pairs not crossing the reservoir. Colored vertical lines indicate different phases in the geothermal operations sequence leading to the gas kick. Concluding remarks Passive seismic methods have been able to emerge in the geophysicist toolbox mainly thanks to the evolution of seismic acquisition technologies, which finally allowed for continuous recordings and storage of the ambient seismic signal instead of simple “triggered” recordings. This major change ultimately allowed scientists to investigate and develop a large scope of tools and methods using a passive seismic approach bringing value for many geoscience fields including geothermal characterization and monitoring. Today, enhancing the potential of passive seismic methods still depends on, and will benefit from technological advances in the acquisition process. Typical key characteristics that are being proposed in recently produced seismic sensors or in phase of implementation for future models are: • Autonomy, with longer lasting batteries for autonomous nodes in the context of monitoring. • Real-time communication of the data, to avoid multiple intervention on site to retrieve the data and allow quasi-continuous monitoring.
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