The earth has a self potential so if you dig two holes a distance apart and measure it with a voltmeter you will get voltage. This would dwarf quartz resonance etc. but I would say if you are dealing with a fault line with quartz then any potential over that would come from groundwater flow. As an aside you can use self potential to map subsurface geology.
If you are looking at measuring heat from an underground event remember if the event is at depth say 5km then the heat is generated there. Imagine a sphere around that zone extending to the surface as the heat will be dissipated through that volume and would be a very small change at the surface over a very large area. In any event if you don't know what the readings were prior to any event how do you measure a change in heat which is what you are after?
Jon
If you are looking at measuring heat from an underground event remember if the event is at depth say 5km then the heat is generated there. Imagine a sphere around that zone extending to the surface as the heat will be dissipated through that volume and would be a very small change at the surface over a very large area. In any event if you don't know what the readings were prior to any event how do you measure a change in heat which is what you are after?
Jon