Forecasting earthquakes has attracted considerable attention recently but thus far there is no suitable explanation as to why non-seismic pre-earthquake manifestations exist. Friedemann Freund proposed the theory that the existence of peroxy defects and positive holes in rocks explained these phenomena and so attempted to lay the scientific basis for the cause of many earthquake precursor signals (Freund, 2006). Freund’s theory was later expanded to show how the redox conversion of OH − pairs into peroxy anions and molecular H2 works. Freund showed that by maintaining thermodynamic rules (Freund and Freund, 2015).
Pre-seismic events such as thermal infrared emissions, surface temperature anomalies, radon irregularities and changes in physical and chemical properties of groundwater prior to major earthquakes have been reported (Tramutoli et al., 2005; Piroddi et al., 2014; Guangmeng, 2008, Ouzounov et al., 2006; Singh et al., 2016; Biagi et al., 2000; Fidani et al., 2017). Anomalies in pH, conductivity or variations in ion content of groundwater can be explained through the interaction between positive holes and water (Grant et al., 2011). Within stressed rock peroxy links can break. When this occurs an electron next to O2− anion is transferred onto the broken peroxy link. The electron donor changes its valence from 2- to 1- (Balk et al., 2009). An O− surrounded by O2− (termed as “positive hole”) is an oxygen anion defect by 1 electron in the O2− anion sublattice and acts as a charge carrier h. (Griscom, 2011; Freund and Freund, 2015). These charge carriers flow out of stressed rock regions and into less stressed rock regions where they can interact with groundwater.
The charge carriers are chemically seen highly oxidizing O− radicals. These radicals can oxidize water to hydrogen peroxide H2O2 on the rock–water boundary and partially oxidize organic compounds dissolved in the groundwater. The partial oxidation of organic compounds can cause a shift in fluorescent intensity and in the fluorescent spectrum (Grant et al., 2011). An example is the oxidation of terephthalates where an O− radical is added to the aromatic ring which leads to a detectable change in the fluorescent spectrum (Saran and Summer, 1999). However, exactly which dissolved organic substances are present in the oxidation reaction involving the charge carriers and their change in the fluorescent spectrum is not yet known.
The reaction between the charge carriers and the groundwater showing an increase in the fluorescent intensity signal could provide evidence of increasing tectonic stress rates in the subsurface.
A limited number of studies have monitored fluorescent intensities using long interval measurements with a flow-through fluorometer. Fluorescent intensity changes were first observed in 1999 using synchronous scans of fluorescent spectra in water samples taken by chance prior to and after a strong earthquake (Balderer and Leuenberger, 2007, Grant, R.A., T. Halliday, W.P. Balderer, F. Leuenberger, M. Newcomer, G. Cyr, F.T. Freund. 2011, Fidani et al., 2017. Our study is one of the first to monitor fluorescent intensities over a time of 11 weeks in two different springs in the northern part of Switzerland. Changes in fluorescent intensities are correlated in our study with the seismic data of nearby stations to deduce potential coincidences. The method of fluorescent monitoring used in our study and the geological and tectonic setting of our chosen physical area in Baden and Rheinfelden Switzerland are explained. Subsequently, the results are presented, discussed and conclusions about the method are drawn.