Mathematical postprocessors have been developed in cooperation with NEDO to calculate time-dependent earth-surface distributions of geophysical observables such as microgravity, electrical self-potential, apparent resistivity (from either DC or MT surveys), seismic velocity/attenuation, and geomagnetic force. The temporal changes are caused by changing underground conditions (pressure, temperature, salinity, gas saturation, etc.) as computed by numerical unsteady multidimensional thermohydraulic reservoir/aquifer simulations. Although the initial application was for monitoring geothermal reservoirs during fluid production and reinjection, the postprocessors can be applied to various subsurface phenomena associated with groundwater in addition to management of geothermal resources.