also, there is some recent work involving attempting to tap telluric currents that are converted into mechanical expansion, and conversely, from compression into current that then propagates through conductive and capacitative materials, including quartzite materials, which are usually found deep in bedrock of massifs like the rockies, alps, the central balkans, carpathians, the caucasus, the mongolian plateaus, the andes, and others.
not much success with these so far but experiments have enabled scavenging of energy in the form of electricity that can power a ground installation where such rock is found, sufficient to power small devices, combined with batteries to capture the energy when it comes out of the crystalline rocks.
note that the radar technique called SAR https://en.wikipedia.org/wiki/Synthetic-aperture_radar that was used to discover a possible massive structure under the great pyramids is likely an ancient quartz device that captures underground vibrations and converts them to electricity, for, as at least one researcher is speculating, synthesising fertilizers (as electrochemical transformation of nitrogen and other materials can convert them to available nitrates, at least, probably other important nutrient ions as well).
SAR works by detecting these vibrations in the ground and using holography techniques to synthesise a 3d model of the echoes of the differently dense materials under the ground. so very likely, a similar method can be used to detect potential sources, as well as, obviously, instead of just trying to tap the natural rocks, to dig into areas of mild seismic motion to place large volumes of quartz crystal to precisely convert the compression force into current.
i'm sure i'm not inventing this idea either, and someone is already looking at ways to do it.
for a simple example, under highways, such crystal based materials packed together in sections could provide power for at least sensors, and maybe emergency communications and lighting systems, powering network routers to run networks to carry signals along these, and exploit the constant vibration of traffic to power the devices. similarly, the flexion of sky scrapers from wind and seismic flows, even potentially a thermo-mechanical coupling could be used to take heat, use it to cause vibrations, and then capture the current this way.
i'm sure the possibilities are only just being started to be explored. if you consider how many industrial and urban settings involve waste energy coming from vibrations, not only could this power devices, likely, these installations could mitigate some of the strain causued by the vibrations as the quartz absorbs it, and when the current is allowed to flow, the energy is extracted from the system.
