Publication Date:
2019
Description:
Abstract
Hydrochemical changes before and after earthquakes have been reported for over fifty 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 2 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 pre‐seismic changes based on five parameters (Na, Si, K, δ18O and δ2H) and post‐seismic 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 pre‐seismic changes were caused by source mixing which resulted in a shift from equilibrium and triggered water‐rock interaction, (2) post‐seismic 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.
Print ISSN:
2169-9313
Electronic ISSN:
2169-9356
Topics:
Geosciences
,
Physics
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