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

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 post-mainshock peaks in trace element concentrations, but little change in major elements. Most parameters returned to pre-earthquake 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 flowpaths. These fluids were expelled into the main flow paths after an increase in pore pressure, hydraulic conductivity, and shaking from co-seismic 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 \u3b413CDIC values closest to a deep magma source to the west became enriched relative to pre-earthquake values following the August 24th 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 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

Hydrogeochemical and isotopic study of thermal and mineralized waters from the Nevsehir (Kozakli) area, Central Turkey

In the Kozakli geothermal province, thermal waters are manifested along a valley 1.5 km long and 200 m in width. Thermal waters utilised by the resort and some other hotels are mostly discharged from bore wells. The issuing temperatures of the thermal waters vary from 40-50 degrees C in thermal springs and 45-96 degrees C in bores and open wells. The geochemical and isotopic signatures of the thermal water suggest mixing of thermal waters with formation waters and cold near-surface groundwaters before emerging to the surface, and hence geochemical indicators fail to indicate the near true reservoir temperatures. However, the oxygen and hydrogen isotopic signatures strongly suggest a high temperature reservoir (>220 degrees C) in the crystalline basement rocks. Long circulation of meteoric waters within the basement rocks is indicated by low tritium values in the thermal waters. Major involvement of Miocene Marls in modifying the chemical signatures of the thermal waters is inferred from the trace element concentrations. (C) 2011 Elsevier B.V. All rights reserved