Hydrochemical Changes Before and After Earthquakes Based on Long‐Term Measurements of Multiple Parameters at Two Sites in Northern Iceland—A Review

Abstract

Hydrochemical changes before and after earthquakes have been reported for over 50 years. However, few reports provide sufficient data for an association to be verified statistically. Also, no mechanism has been proposed to explain why hydrochemical changes are observed far from earthquake foci where associated strains are small (<10−8). Here we address these challenges based on time series of multiple hydrochemical parameters from two sites in northern Iceland. We report hydrochemical changes before and after M >5 earthquakes in 2002, 2012, and 2013. The longevity of the time series (10 and 16 years) permits statistical verification of coupling between hydrochemical changes and earthquakes. We used a Student t test to find significant hydrochemical changes and a binomial test to confirm association with earthquakes. Probable association was confirmed for preseismic changes based on five parameters (Na, Si, K, δ18O, and δ2H) and postseismic changes based on eight parameters (Ca, Na, Si, Cl, F, SO4, δ18O, and δ2H). Using concentration ratios and stable isotope values, we showed that (1) gradual preseismic changes were caused by source mixing, which resulted in a shift from equilibrium and triggered water‐rock interaction; (2) postseismic changes were caused by rapid source mixing; and (3) longer‐term hydrochemical changes were caused by source mixing and mineral growth. Because hydrochemical changes occur at small earthquake‐related strains, we attribute source mixing and water‐rock interaction to microscale fracturing. Because fracture density and size scale inversely, we infer that mixing of nearby sources and water‐rock interaction are feasible responses to small earthquake‐related strains.

CO2 Inflow and Elements Desorption Prior to a Seismic Sequence, Amatrice‐Norcia 2016, Italy

“…As a result, it is very difficult to relate the geochemical anomalies to a specific process and prove that are really associated with earthquakes. Despite this, water chemical anomalies are increasingly recorded at distances between 20 km and more than 200 km from strong earthquake epicenters (Andrén et al, 2016;Chen et al, 2015;Claesson et al, 2004;De Luca et al, 2018;Grant et al, 2011;Huang et al, 2012;Igarashi et al, 1995;Inan et al, 2012;Ingebritsen & Manga, 2014;Sano & Wakita, 2016;Skelton et al, 2008Skelton et al, , 2014Skelton et al, , 2019Wakita et al, 1988;Wang & Manga, 2010;Wästeby et al, 2014;Zeng et al, 2015).…”

In situ observation of helium and argon release during fluid-pressure-triggered rock deformation

“…Chemical anomalies created by earthquakes have been explained by the mixing of fluids from different sources (with different chemical compositions) inhibited by changes in flow pathway geometry and hydraulic properties during stress build-up and failure 15,16 . Laboratory studies have also observed the emergence of concentration anomalies in noble gases during rock deformation experiments [17][18][19][20] .…”

The Bortoluzzi Mud Volcano (Ionian Sea, Italy) and its potential for tracking the seismic cycle of active faults

“…300 m). The dimensions of the conduit and paleoflows are not visible in the seismic profiles, for example the Christmas-tree structures described by Somoza et al (2003). From previous literature (e.g., Kioka and Ashi, 2015), we can only infer that the BMV dimensions and its computed volume suggest a polygenetic behavior, so we argue that the main fluid conduit has possibly been utilized several times to increase the volume of the volcano itself.…”