“…Thermal perturbations to underground formations can be caused by injecting fluids of different temperature into the deep subsurface or by natural recharge of surface water with sinusoidally time-varying temperature into the shallow subsurface. Relevant applications involving fluid injection may be directly related to energy storage and production, such as for thermal oil recovery (Kuhn & Koch, 1953;Walter, 1957), aquifer thermal energy storage (Andersson et al, 2013;Meyer & Todd, 1973;Nordbotten, 2017;Tsang et al, 1982), and geothermal energy production (Bodvarsson & Eggers, 1972;Harlow & Pracht, 1972), or they may not be energy related, such as for waste-water disposal, water flooding for secondary oil recovery, and geological CO 2 storage. Relevant applications in the latter include estimating the rate of groundwater recharge using field temperature measurements (Bredehoeft & Papadopulos, 1965;Constantz et al, 2002;Hatch et al, 2006;Silliman et al, 1995;Stallman, 1965;Suzuki, 1960).…”