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Mechanisms of earthquake‐induced chemical and fluid transport to carbonate groundwater springs after earthquakes

August 6, 2018

Mechanisms by which hydrochemical changes occur after earthquakes are not well documented. We use the 2016–2017 central Italy seismic sequence, which caused notable hydrochemical transient variations in groundwater springs to address this topic, with special reference to effects on fractured carbonate aquifers. Hydrochemistry measured before and after the earthquakes at four springs at varying distances from the epicenters all showed immediate postmainshock peaks in trace element concentrations but little change in major elements. Most parameters returned to preearthquake values before the last events of the seismic sequence. The source of solutes, particularly trace elements, is longer residence time pore water stored in slow‐moving fractures or abandoned karstic flow paths. These fluids were expelled into the main flow paths after an increase in pore pressure, hydraulic conductivity, and shaking from coseismic aquifer stress. The weak response to the later earthquakes is explained by progressive depletion of high solute fluids as earlier shocks flushed out the stored fluids in the fractures. Spring δ13CDIC values closest to a deep magma source to the west became enriched relative to preearthquake values following the 24 August event. This enrichment indicates input from deeply sourced dissolved CO2 gas after dilation of specific fault conduits. Differences in carbon isotopic responses between springs are attributed to proximity to the deep gaseous CO2 source. Most of the transient chemical changes seen in the three fractured carbonate aquifers are attributed to local shaking and emptying of isolated pores and fractures and are not from rapid upward movement of deep fluids.

Publication Year 2018
Title Mechanisms of earthquake‐induced chemical and fluid transport to carbonate groundwater springs after earthquakes
DOI 10.1029/2017WR022097
Authors Michael R. Rosen, Gilberto Binda, Claire Archer, Andrea Pozzi, Alessandro Michetti, Paula Noble
Publication Type Article
Publication Subtype Journal Article
Series Title Water Resources Research
Index ID 70198523
Record Source USGS Publications Warehouse
USGS Organization Office of the Associate Director for Water