Microseismic Events Cause Significant pH Drops in Groundwater

Earthquakes cause rock fracturing, opening new flow pathways which can result in the mixing of previously isolated geofluids with differing geochemistries. Here, we present first evidence that seismic events significantly reduce groundwater pH without requirement for fluid mixing, solely through process dynamic fracturing. At Grimsel Test Site, Switzerland, observe repeated, short-lived drops 1–3.5 units, while major and minor ion concentrations remain constant. Acidification coincides reservoir drainage induced microseismic events. In laboratory experiments, demonstrate fresh surfaces made by particle cracking interact situ water molecules, likely creation surface silanols silica radicals, increasing H+ concentration lowering pH. Our findings are significant; exerts a fundamental control on rate outcome most aqueous geochemical reactions commonplace, even seismically inactive regions.