The heat of the subsurface is referred to as geothermal energy and may be regarded as a result of heat flow from the earth’s core and mantle and heat production from the decay of radioactive isotopes (locally) in the rocks of the crust.
Deep geothermal energy is often denoted hot dry rock (HDR) power and if the permeability of the deep reservoir is improved by e.g. cracking the rock by hydraulic fracturing (water under high pressure), it may be denoted an enhanced geothermal system (EGS).
Naturally occurring earthquakes can occur anywhere at any time, and if not controlled by local microseismic monitoring networks in order to distinguish them from induced microseismic activity, public concern may become an effective showstopper for geothermal projects. A first step in the mitigation of large induced seismic events is a proper monitoring of the microseismicity.
For such purpose seismic sensors are generally installed in observational boreholes drilled to an appropriate depth around the production wells or superficially with proper passive seismic stations.