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Effects of seismic activity on the fluorescence signal of groundwater

Effects of seismic activity on the fluorescence signal of groundwater Background: Peroxy defects in minerals from stressed igneous and high grade metamorphic rocks release charge carriers which are highly mobile. This process is proposed as the main cause of observed pre-seismic phenomena such as infrared emission on the surface, positive air ionization or a change of ground water chemistry. The primary changes in groundwater chemistry is caused through an increase in oxidation on the rock-water-boundary. This can be detected by observing a rise in fluorescence due to an O addition on an aromatic ring which can change a substance. For example a terephthalate can change from a non-fluorescent to a partially fluorescent compound due to O additions. Results: In this paper we present results of groundwater fluorescence monitoring over a period of approximately three months. We observe distinct wavelengths with an on-line flow-through fluorometer in two different thermal springs in the northern part of Switzerland. We will also show that fluorescent intensities fluctuate widely and display clear increases and sharp rapid drops. During the measuring period many smaller earthquakes with a magnitude between 1.0 and 2.6 occurred close to the measuring stations but a strong earthquake was absent. Nevertheless, an increase in fluorescent intensity was measured in both springs prior to a magnitude 2.2 earthquake. After this seismic event the fluorescent intensities suddenly decreased. Conclusions: The presented results comply with the anticipated theoretical considerations. Keywords: Peroxy defects, Positive holes, Groundwater, Monitoring fluorescence, Seismic activity, Earthquake precursor Background groundwater prior to major earthquakes have been re- Forecasting earthquakes has attracted considerable ported (Tramutoli et al., 2005; Piroddi et al., 2014; attention recently but thus far there is no suitable Guangmeng, 2008, Ouzounov et al., 2006; Singh et al., explanation as to why non-seismic pre-earthquake mani- 2016; Biagi et al., 2000; Fidani et al., 2017). Anomalies in festations exist. Friedemann Freund proposed the theory pH, conductivity or variations in ion content of ground- that the existence of peroxy defects and positive holes in water can be explained through the interaction between rocks explained these phenomena and so attempted to positive holes and water (Grant et al., 2011). Within lay the scientific basis for the cause of many earthquake stressed rock peroxy links can break. When this occurs 2− precursor signals (Freund, 2006). Freund’s theory was an electron next to O anion is transferred onto the later expanded to show how the redox conversion of broken peroxy link. The electron donor changes its − − OH pairs into peroxy anions and molecular H works. valence from 2- to 1- (Balk et al., 2009). An O sur- 2− Freund showed that by maintaining thermodynamic rounded by O (termed as “positive hole”) is an oxygen 2− rules (Freund and Freund, 2015). anion defect by 1 electron in the O anion sublattice Pre-seismic events such as thermal infrared emissions, and acts as a charge carrier h (Griscom, 2011; Freund surface temperature anomalies, radon irregularities and and Freund, 2015). These charge carriers flow out of changes in physical and chemical properties of stressed rock regions and into less stressed rock regions where they can interact with groundwater. * Correspondence: werner.balderer@erdw.ethz.ch The charge carriers are chemically seen highly oxidiz- Geological Institute, ETH Zürich, Sonneggstrasse 5, 8092 Zürich, Switzerland ing O radicals. These radicals can oxidize water to Full list of author information is available at the end of the article © The Author(s). 2018 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Mäder et al. Geoenvironmental Disasters (2018) 5:9 Page 2 of 9 hydrogen peroxide H O on the rock–water boundary Method 2 2 and partially oxidize organic compounds dissolved in A commercially available fluorometer (GUGN-FL30) the groundwater. The partial oxidation of organic com- developed by the University of Neuchatel to detect pounds can cause a shift in fluorescent intensity and in events of artificial fluorescence tracer tests, was used for the fluorescent spectrum (Grant et al., 2011). An example the continuous monitoring of fluorescence at both is the oxidation of terephthalates where an O radical is spring sites observed. added to the aromatic ring which leads to a detectable An optical system is located inside the flow-through change in the fluorescent spectrum (Saran and Summer, fluorometer. Water flows through a quartz tube within a 1999). However, exactly which dissolved organic steel case in this device. It is crucial to maintain continu- substances are present in the oxidation reaction involving ous water flow in the measurement tool. To achieve this the charge carriers and their change in the fluorescent end, the fluorometer was installed at a lower height than spectrum is not yet known. the water flow. The reaction between the charge carriers and the Occasional removal of calcareous deposits inside the groundwater showing an increase in the fluorescent tube is essential to ensure that measurements were intensity signal could provide evidence of increasing not adversely affected by these deposits. In our study tectonic stress rates in the subsurface. at both spring sites, the calcareous deposits were not A limited number of studies have monitored fluores- significantly large enough due to the limited measur- cent intensities using long interval measurements with ing period. Therefore, the influence of the purgation a flow-through fluorometer. Fluorescent intensity on the fluorescence measurement was assumed to be changes were first observed in 1999 using synchronous insignificant and a correction analysis for the purga- scans of fluorescent spectra in water samples taken by tion was neglected. chance prior to and after a strong earthquake (Bal- The optical system consists of four different LEDs. derer and Leuenberger, 2007,Grant,R.A., T.Halliday, Each light source has a specific wavelength. In this case W.P. Balderer, F. Leuenberger, M. Newcomer, G. Cyr, 370 nm, 470 nm, 525 nm and 660 nm were used to F.T. Freund. 2011,Fidaniet al., 2017.Our studyisone excite the fluorescent components in the water. The of the first to monitor fluorescent intensities over a emission optics are arranged perpendicular to the excita- time of 11 weeks in two different springs in the north- tion plains. The emissions of the fluorophores are ern part of Switzerland. Changes in fluorescent inten- filtered to determine the wavelength range detected by sities are correlated in our study with the seismic data photodiodes (Schnegg, 2002). The monitored measure- of nearby stations to deduce potential coincidences. ment interval of the fluorescence intensity in mV was The method of fluorescent monitoring used in our 300 s. The schematic concept of the fluorometer is study and the geological and tectonic setting of our shown in Fig. 1. chosen physical area in Baden and Rheinfelden A high turbidity (mainly caused by degassing) can Switzerland are explained. Subsequently, the results adversely influence the intensity of the fluorescent are presented, discussed and conclusions about the measurements. In the case of the Rheinfelden spring method are drawn. where a high CO content exists, a degassing device was Fig. 1 Schematic functional sketch of the installed flow-through fluorometer of the type GUGN – FL30. The light sources with the specific wavelengths namely, 370 nm, 470 nm, 525 nm and 660 nm and corresponding detector ends are represented together with arrows perpendicular to the main water through flow tube (modified after Schnegg 2002) Mäder et al. Geoenvironmental Disasters (2018) 5:9 Page 3 of 9 installed to reduce turbidity. Besides degassing and (Muschelkalk and Keuper) from the early Mesozoic era turbidity, a possible mixing of the thermal spring water (Burger, 2009). Rheinfelden is situated in close vicinity to with a neighbouring aquifer can influence the fluores- the Rhine Graben-structure, a 300–350 km long rift where cence signal. The order of magnitude by which the the geology and tectonics have been studied in detail (Sis- fluorescence intensity is affected by such a mixing de- singh, 1998;Becker, 2000;Ustaszewski and Schmid, 2007). pends on the constituents of the inflowing aquifer. An- The detailed well profile of the Rheinfelden spring is pre- thropogenic influxes in the form of chemicals such as sented by Ryf (1984). cleaning agents from nearby industry or thermal baths The thermal springs of Baden lie in the “Lägeren”– resorts could also adversely influence measurements structure where the Limmat eroded into the Muschelkalk taken. layers in the eastern part of the Faltenjura. The Baden hot spring contains fluids originating from the base rock Geological and tectonic setting of the ascending through the evaporites of the middle investigated springs of Baden and Rheinfelden Muschelkalk layers, along a tectonic fault, which is The measurements presented here originate from an characterized as the Jura-Overthrust (Burger, 2009; unused thermal deep well at Rheinfelden (latitude Löw, 1987;Nagra, 2014,Fig. 3.3–2). The aquifer has 47.5505°, longitude 7.8058°) and from a hot spring in a piezometric head of 359 m a.s.l. and is therefore ar- Baden (latitude 47.4808°, longitude 8.3130°). The geo- tesian against the local river Limmat (350 m a.s.l.) logical overview of Switzerland is presented in Fig. 2 and the surrounding groundwater streams (348– whereas the tectonic setting and the seismicity of the in- 357 m a.s.l.) (Löw, 1987). The Baden spring water vestigated area are presented in Fig. 3. with a total mineralization of around 4.5 g/l and a The Rheinfelden thermal well temperature is 12 °C conductivity of 5970 μS/cm and is hydro-chemically with a pH of 6.6 and a conductivity of 5420 μS/cm. characterized by Na-Ca-(Mg)-Cl- SO type and con- This well contains Na-Ca-Cl-HCO -SO thermal tains higher amounts of characteristic dissolved gas- 3 4 water with a high CO content and originates at a ses, namely H S(3.0mg/l),CH (< 0.3 mg/l) and 2 2 4 depth of 550 m. Geologically it is in late Palaeozoic sedi- CO (292 mg/l) (Rick, 2007;Högl, 1980). The water ments (Perm, Rotliegendes) below dense evaporitic layers has a temperature around 46 °C and a pH of 6.6. Fig. 2 Geological Map Switzerland and the bordering countries of France and Germany. Switzerland is high-lighted in green on the map of Europe on the right side. The size of the geological map of Switzerland including the four main distinctive units namely, Faltenjura (blue), Molassebecken (yellow), Helvetikum (green) and Kristallin (pink, including the Aar-Massiv, bright-red) is illustrated on the left side. The two Fluorescence monitoring locations Rheinfelden (R) and Baden(B) are presented by bold black dots (modified after swisstopo, BWG). Mäder et al. Geoenvironmental Disasters (2018) 5:9 Page 4 of 9 Fig. 3 Map of the area of Northern Switzerland and the bordering countries of France and Germany with represented magnitudes of the main occurring earthquakes. The two Fluorescence monitoring locations Rheinfelden (R) and Baden (B) are indicated with bold blackish dots. The reddish lines represent the main tectonic faults in the nearby area of the measurement locations. The greyish circles illustrate the locations of the registered earthquakes since 2001. The size of the circles corresponds to the magnitude of the earthquakes according to the legend on the right side of the figure (modified after SED) Fig. 4 Diagram of the monitored Fluorescence intensity of the thermal water in Baden (B) over the measuring period. The fluorescence intensity at wavelength 470 nm is presented in the blueish curve whereas the greyish curve presents the fluorescence intensity at 525 nm. The orange squares depict the registered earthquakes with the location and the magnitude in brackets. The earthquakes are scaled depending on their precursor manifestation zone, which was calculated by Eq. 1 Mäder et al. Geoenvironmental Disasters (2018) 5:9 Page 5 of 9 Fig. 5 Diagram of the monitored Fluorescence intensity of the thermal water in Rheinfelden (R) over the measuring period. The fluorescence intensity at wavelength 470 nm is presented in the blueish curve whereas the greyish curve presents the fluorescence intensity at 525 nm. The orange squares depict the registered earthquakes with the location and the magnitude in brackets. The earthquake close to Albstadt (E3) does not appear on the figure because of the distance between the measurement location and the epicenter, which exceeded 100 km. The earthquakes are scaled depending on their precursor manifestation zone, which was calculated by Eq. 1. The blackish – dashed line marks the interruption of the measurement because of the loss of power supply Results approach assumes that non-mechanical precursors are The following figures (Figs. 4 and 5) show fluorescent caused by deformation of the surrounding medium. intensities over the measured time and the location and The theory states that a possible manifestation of a magnitude of the earthquakes that occurred. Only precursor occurs within the strain radius and can be earthquakes which had a magnitude 1 or higher and detected when the monitoring site lies inside this were experienced within a radius of 100 km from the estimated zone. The calculation of the strain combines spring site measurement location were considered. Out the impact of the magnitude and the distance to the of the four possible wavelength sensors only the most monitoring site. This result helps predict if a precursor significant results are presented. These were using the is expected at the measurement site or not. According 470 nm and 525 nm signals. The strain (ε) and strain to Dobrovolsky et al. (1979) lies the monitoring side radius of the nearby registered earthquakes are calcu- inside the deformation zone if the determined strain is − 8 lated using the Dobrovolsky relation (Eqs. 1 and 2) above 10 . However, whether the monitoring site lies (Dobrovolsky et al., 1979). inside the strain radius is not that significant when the expected changes in fluorescence intensities are assumed 0:43M 10 ¼ strain radius ð1Þ to be caused through the stress activated charge carriers. It has been demonstrated in lab experiments that these 1:3M−8:19 charge carriers are highly mobile and it is assumed that 10 ¼ ε ð2Þ they can propagate far away from the stressed rock region (Freund and Freund, 2015; Scoville et al., 2015). The strain radius is the estimated zone around the Nevertheless, the strain and the strain radius were epicentre of an effective manifestation of precursor calculated to follow the initial scaling approach of earth- deformation and is dependent on the magnitude M of quake precursors and to get a rough estimation of the the earthquake (Dobrovolsky et al. 1979). This relation is extent of the deformation zone. The positive holes are a very useful approach to obtain a semi-quantitative generated in the deformation zone and therefore it is number for the precursor manifestation zone. This expected that stronger earthquakes with larger Mäder et al. Geoenvironmental Disasters (2018) 5:9 Page 6 of 9 Table 1 The registered earthquakes during the measuring period with a magnitude higher than 2.0 are listed below with the corresponding geographical coordinates (Lat / Long), magnitude (M) and depth of the earthquakes. E1, E2, E3, E4 are identification numbers for the earthquakes which are mapped in Figs. 4, 5 and 6. The distances between the epicentres and the measurement locations Baden (B) and Rheinfelden (R) were calculated. The strain radius was calculated by means of Eq. 1. Strains at the monitoring site R and B are calculated by Eq. 2 Earthquake Lat / Lon [°] M Depth [km] Distance to B [km] Distance to R [km] Strain radius [km] Strain ε at: B Strain ε at: R −11 −11 E1 46.90 / 7.42 2.6 5.7 93.3 77.9 13.1 1.91*10 3.28*10 −12 −11 E2 47.15 / 7.15 2.4 9.8 95.0 66.5 10.8 9.93*10 2.89*10 −11 − 11 E3 48.24 / 9.05 2.5 9.6 100.0 > 100 11.9 1.15*10 < 1.15*10 −11 − 11 E4 47.66 / 8.74 2.2 7.4 37.7 71.0 8.8 8.73*10 1.31*10 deformation zones tend to activate more charge carriers mainly caused by short intervals of high CO overpres- than weaker ones. Therefore, only earthquakes with sure and outgassing. The reason behind is the thermal magnitude higher than 2.0 were considered for the strain water of the Baden spring is CO oversaturated and respectively strain radius calculations and as possible outgases through pressure decrease with the natural detection targets. The four registered earthquakes with a ascendance of the water. This outgassing process does magnitude higher than 2.0 are listed in Table 1 and not happen continuously. It is more a periodical process. mapped in Fig. 6. Data and information about registered The measured course of fluorescent signal at 470 nm earthquakes are provided from the SED (Swiss Seismo- shows one gradual increase (April 23th 2015 – May 4th, logical Service). 2015) of more than 1 mV which is followed by a signifi- cant rapid drop. The other obvious event is a significant Results: Baden jump in intensity to 8 mV within 3 days and followed by The measured fluorescence intensity at wavelength of a wide fluctuation until a significant rapid drop occurred 470 nm which is shown in Fig. 4 fluctuated widely (June 1st, 2015). The fluorescence intensity at wavelength around 4 mV whereas the intensity at wavelength of 525 nm shows a similar but not identical behaviour as the 525 nm fluctuated around 2 mV. The measurements signal at 470 nm. During the survey, many smaller sometimes showed dispersions in the fluorescent inten- earthquakes within a radius of 100 km happened. The sity within a small-time interval. These events were earthquakes close to Bern (E1) with a magnitude of 2.6 Fig. 6 Map of Switzerland with representation of all the earthquakes, which were registered within a time span of 90 days before the fluorescence monitoring was stopped are highlighted in the map of Switzerland by yellow dots. The size of the circles corresponds to the magnitude of the earthquakes according to the legend on the right side. The location of the earthquakes from Table 1 are highlighted with the blackish arrows. The measurement locations Baden (B) and Rheinfelden (R) are indicated by the bolt blackish dots (modified after SED) Mäder et al. Geoenvironmental Disasters (2018) 5:9 Page 7 of 9 and Albstadt (E3) with magnitude 2.5 were the strongest rock regions. When more charge carriers are generated, but both epicentres were relatively far (E1: 93.3 km, E3: the oxidation on the rock–water boundary is increased 100.0 km) from the measuring station (B) (Table 1,Fig. 6). and the fluorescence intensity rises. The expected shape The seismic event E1 was the strongest earthquake with a and the duration of the increasing fluorescence intensity corresponding strain radius of 13.1 km. The earthquake curve prior to an earthquake is not known yet but it is from May 31th 2015 around Andelfingen (E4) with mag- assumed that it is most likely variable. nitude 2.2 lay just 37.7 km away from the station B and is The theory assumes that the higher the magnitude of therefore of most interest for our studies. All calculated an earthquake is, the higher the impact of the fluores- strains at monitoring site B are below the threshold of 10 cent signal in the measured groundwater will be. and lie therefore outside the deformation zone. Because of the lack of strong seismicity in close vicinity to the monitoring stations during the measuring period Results: Rheinfelden it is difficult to determine correlations between changes The monitored fluorescence intensity curves of Rhein- in fluorescence and earthquakes. felden, measured at wavelengths 470 nm and 525 nm The calculated strains of the earthquakes E1 – E4 for are presented in Fig. 5. The intensity at 470 nm fluctu- both monitoring sites are much smaller than the postu- − 8 ated widely with a range from 1.6 mV to 4.1 mV. The lated 10 . This means that these four earthquakes fluorescence signal at 525 nm shows an almost identical should not manifest themselves at the monitoring site behaviour as the signal at 470 nm but with lower fluor- using the Dobrovolsky approach. However, all the four escent intensities. Despite an installed outgassing earthquakes (E1 – E4) happened at very shallow depths device, the very high CO content of the Rheinfelden and it should be considered that the stress generated spring caused a greater dispersion of the signals than in charge carriers can flow much further than the strain the Baden measurements. The beginning of the meas- radius estimates. uring period is dominated by a rapid increase from At the Rheinfelden spring site the fluorescence signal 1.8mVto4.1 mV with twomain rapid drops, which steadily increased until the earthquake (E1) with a interrupts the gradual increase in fluorescence intensity magnitude of 2.6 close to Bern happened. Subsequently at 470 nm. Another significant drop (April 24th, 2015) the fluorescence intensity rapidly dropped after the happened due to a sudden power loss to the registered earthquake. However, this phenomenon fluorometer which is indicated through the blackish – cannot be clearly identified as a coherence between the dashed line in Fig. 5. This sudden drop in fluorescence fluorescence signal and the earthquake because of the intensity at both wavelengths occurred because of the low magnitude and the large distance to the measuring shut-down (power loss) of the fluorometer and must be station (R). Additionally, on April 11th, 2015 a similar negated for interpretation. After this interruption, the rapid drop in fluorescence intensity occurred but in continuation shows a considerable steady increase at absence of an earthquake. The registered earthquakes both distinctive wavelengths until a sudden drop (May close to Biel (E2) and Albstadt (E3) do not show any 18th, 2015) occurred. The last parts of the curve are possible changes to the fluorescence signals at both dominated by two rapid increases, both of which are spring sites. The earthquake E3 is not reflected in Fig. 5 followed by rapid drops (Fig. 6). Out of the 4 earth- because of the distance, which exceeded the maximum quakes from Table 1, the earthquake close to Biel (E2) distance of 100 km. with a magnitude of 2.4 and a corresponding strain Prior to the earthquake (E4) with a magnitude of 2.2 radius of 10.8 km was the closest earthquake (66.5 km) close to Andelfingen, an increase in fluorescence inten- to the Rheinfelden measurement location (R). However, sity was measured at both spring sites. Moreover, the all the strains at monitoring site R lie below the postu- fluorescence signals suddenly dropped immediately after lated threshold. the earthquake (E4) occurred. The increase and sudden decrease of the fluorescence intensity was more pro- Discussion nounced at the Baden spring (B) than in Rheinfelden The fluorescence intensities vary at moderate magni- (R). The reason behind this could be found in the tudes at both spring sites over the whole monitoring shorter distance from the epicentre to the measuring period. Intervals with stable intensity values are scarce. station in Baden compared to the distance to Rheinfel- The main trend of the observed fluorescence monitoring den. This recorded specific change in fluorescence is dominated by several increases which are followed by intensity is quite remarkable because of its occurrence at sudden decreases in fluorescent intensities. both spring sites prior to and after the earthquake. Such Intensified tectonic stresses in the subsurface leads to an event in fluorescence change would be expected and an increase of stress generated charge carriers which would be consistent with the theory of the release of flow out of the stressed rock region into the less stressed stress generated charge carriers which cause an oxidation Mäder et al. Geoenvironmental Disasters (2018) 5:9 Page 8 of 9 of the groundwater. However, that this change in the the Dobrovolsky relation〖10〗^(0.43*M) strain radius of the nearby registered earthquakes are calculated using the Dobrovolsky relation fluorescence signal can be identified because of increased and diminished tectonic stresses in the subsurface is Acknowledgements beyond the current understanding of the phenomena. Very special thanks goes out to Mr. Kost and the RehaClinic team Baden and to Mr. Franz Resnig, Thermal spa foundation. Dr. Barbara Reyes-Trüssel, Nevertheless, this method could be a useful tool in future Geophysicist at EBERHARD & Partner AG for providing the possibility to use earthquake forecast because of its sensitivity to a wide the deep borehole at Rheinfelden for on-line measurements, Mr. Lehman catchment area which depends on the extent of the and the city of Rheinfelden for the support they provided us during the survey. aquifer and its flowrate. Furthermore, the modest method- ology and the straightforward installation and mainten- Funding ance of the fluorometer is another point in favour of this This published research was not subject of any special funding and results from the normal program of education studies of ETH in the frame of Earth monitoring method. The limitation of the method lies in Science Department. The applied instruments are property of the Geological the strong influence of outgassing and turbidity on the Institute, Engineering Geology and of the hydrological section of the Swiss fluorescence signal of the groundwater. External factors Federal Institute for Forest. which influence the fluorescence intensity besides aquifer Availability of data and materials mixing and anthropogenic influxes are not yet known and The fluorescence datasets supporting the conclusions of this article are further research is needed. included within the article. The information on the registered earthquakes is available in the repository of the SED: http://www.seismo.ethz.ch The information on the flow-through fluorometer is available on: http:// Conclusion www.albillia.com The results presented clearly show the variability of Authors’ contributions fluorescence intensity of ground water at the distinct Dr. WB was as Senior lecturer supervisor of the presented study and Co- wavelengths. Furthermore, the results support a possible Author and organized the availability of investigated test sites, setup of instruments, instruction of maintenance and exploitation and interpretation link between the stress generated charge carriers caused of fluorescence monitoring. MM made the fluorometer measurements by tectonic processes leading to earthquakes and their exploitation, and interpretation of the results and studied the relation to the interaction with the investigated thermal water. However, occurring earthquakes of the related areas in the frame of his thesis of Bachelor of Earth Sciences degree from ETH Zurich. Dr. FL was responsible these preliminary results should be confirmed by further for the lab measurements and the fluorescence synchronous scan spectra monitoring of fluorescence of groundwater at alternate measurements on additional water samples of both investigated thermal groundwater sites in tectonically more active areas. water monitoring sites. All authors read and approved the final manuscript. The selection of appropriate springs or wells is crucial. Authors’ information Most suited for in-situ fluorescence monitoring are sites Werner Balderer was from 1986 to 2010 Lecturer of Isotope Hydrogeology, with artesian groundwater outflow such as the investi- and General Hydrogeology at ETH Zurich, his research interests include Mineral and Thermal water and research on Natural fluorescence of gated Baden spring and the Rheinfelden borehole. groundwater as proxi of tectonic activity. Groundwater of pumped wells are more affected by Matthias Mäder holds a Bachelor of Earth Sciences degree from ETH Zurich disturbances due to pumping intervals and non-steady with a major in geophysics. Matthias is a current Master student in Petroleum Engineering & Geosciences state situations in respect to considering hydraulic head at TU Delft, Netherlands. His research interests includes the understanding of and degassing processes. pre-earthquake phenomena and petroleum geology. Furthermore, the monitoring period should be ex- Ethics approval and consent to participate tended to enhance the probability of earthquake occur- ‘Not applicable’. rences and to allow long term analysis. Fluorometers with a wider wavelength spectrum and an advanced sen- Consent for publication According to the ETH Zurich the bachelor thesis and its publication belongs sitivity would be a further asset. This would allow the to the personal property right of the students of Bachelor degree from ETH wavelength spectrum to be tuned to the most signifi- Zurich. cant wavelengths in terms of changes in fluorescent Competing interests intensities as an earthquake precursor. Furthermore, a All the authors have no competing interests in the research subject of this wider wavelength spectrum could provide further publication. No one is working in industries or has ties to such in the information about possible shifts in fluorescence domain of the published research. Therefore, no financial and non-financial competing interests exist. spectra. Beyond that, further investigations into the oxidation process of dissolved organic compounds in Publisher’sNote the ground water should be done in order to improve Springer Nature remains neutral with regard to jurisdictional claims in the understanding of the phenomena. published maps and institutional affiliations. Abbreviations Author details B: Measuring station in Baden; E1 -E4: Earthquake identification numbers; Department of Geoscience, TU Delft, Stevinweg 1, 2628 CN Delft, GUGN-FL30: type of fluorometer developed by the University of Neuchatel; Netherlands. Geological Institute, Engineering Geology, ETH Zürich, LED: Light emitting diode; M: Magnitude; R: Measuring station in Sonneggstrasse 5, 8092 Zürich, Switzerland. Geological Institute, ETH Zürich, Rheinfelden; ε: strain of the nearby registered earthquakes calculated using Sonneggstrasse 5, 8092 Zürich, Switzerland. Mäder et al. 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A study of variation in soil gas concentration associated with earthquakes near indo-Burma subduction zone. Geoenviron Disaster 3: 22. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Geoenvironmental Disasters Springer Journals

Effects of seismic activity on the fluorescence signal of groundwater

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Abstract

Background: Peroxy defects in minerals from stressed igneous and high grade metamorphic rocks release charge carriers which are highly mobile. This process is proposed as the main cause of observed pre-seismic phenomena such as infrared emission on the surface, positive air ionization or a change of ground water chemistry. The primary changes in groundwater chemistry is caused through an increase in oxidation on the rock-water-boundary. This can be detected by observing a rise in fluorescence due to an O addition on an aromatic ring which can change a substance. For example a terephthalate can change from a non-fluorescent to a partially fluorescent compound due to O additions. Results: In this paper we present results of groundwater fluorescence monitoring over a period of approximately three months. We observe distinct wavelengths with an on-line flow-through fluorometer in two different thermal springs in the northern part of Switzerland. We will also show that fluorescent intensities fluctuate widely and display clear increases and sharp rapid drops. During the measuring period many smaller earthquakes with a magnitude between 1.0 and 2.6 occurred close to the measuring stations but a strong earthquake was absent. Nevertheless, an increase in fluorescent intensity was measured in both springs prior to a magnitude 2.2 earthquake. After this seismic event the fluorescent intensities suddenly decreased. Conclusions: The presented results comply with the anticipated theoretical considerations. Keywords: Peroxy defects, Positive holes, Groundwater, Monitoring fluorescence, Seismic activity, Earthquake precursor Background groundwater prior to major earthquakes have been re- Forecasting earthquakes has attracted considerable ported (Tramutoli et al., 2005; Piroddi et al., 2014; attention recently but thus far there is no suitable Guangmeng, 2008, Ouzounov et al., 2006; Singh et al., explanation as to why non-seismic pre-earthquake mani- 2016; Biagi et al., 2000; Fidani et al., 2017). Anomalies in festations exist. Friedemann Freund proposed the theory pH, conductivity or variations in ion content of ground- that the existence of peroxy defects and positive holes in water can be explained through the interaction between rocks explained these phenomena and so attempted to positive holes and water (Grant et al., 2011). Within lay the scientific basis for the cause of many earthquake stressed rock peroxy links can break. When this occurs 2− precursor signals (Freund, 2006). Freund’s theory was an electron next to O anion is transferred onto the later expanded to show how the redox conversion of broken peroxy link. The electron donor changes its − − OH pairs into peroxy anions and molecular H works. valence from 2- to 1- (Balk et al., 2009). An O sur- 2− Freund showed that by maintaining thermodynamic rounded by O (termed as “positive hole”) is an oxygen 2− rules (Freund and Freund, 2015). anion defect by 1 electron in the O anion sublattice Pre-seismic events such as thermal infrared emissions, and acts as a charge carrier h (Griscom, 2011; Freund surface temperature anomalies, radon irregularities and and Freund, 2015). These charge carriers flow out of changes in physical and chemical properties of stressed rock regions and into less stressed rock regions where they can interact with groundwater. * Correspondence: werner.balderer@erdw.ethz.ch The charge carriers are chemically seen highly oxidiz- Geological Institute, ETH Zürich, Sonneggstrasse 5, 8092 Zürich, Switzerland ing O radicals. These radicals can oxidize water to Full list of author information is available at the end of the article © The Author(s). 2018 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Mäder et al. Geoenvironmental Disasters (2018) 5:9 Page 2 of 9 hydrogen peroxide H O on the rock–water boundary Method 2 2 and partially oxidize organic compounds dissolved in A commercially available fluorometer (GUGN-FL30) the groundwater. The partial oxidation of organic com- developed by the University of Neuchatel to detect pounds can cause a shift in fluorescent intensity and in events of artificial fluorescence tracer tests, was used for the fluorescent spectrum (Grant et al., 2011). An example the continuous monitoring of fluorescence at both is the oxidation of terephthalates where an O radical is spring sites observed. added to the aromatic ring which leads to a detectable An optical system is located inside the flow-through change in the fluorescent spectrum (Saran and Summer, fluorometer. Water flows through a quartz tube within a 1999). However, exactly which dissolved organic steel case in this device. It is crucial to maintain continu- substances are present in the oxidation reaction involving ous water flow in the measurement tool. To achieve this the charge carriers and their change in the fluorescent end, the fluorometer was installed at a lower height than spectrum is not yet known. the water flow. The reaction between the charge carriers and the Occasional removal of calcareous deposits inside the groundwater showing an increase in the fluorescent tube is essential to ensure that measurements were intensity signal could provide evidence of increasing not adversely affected by these deposits. In our study tectonic stress rates in the subsurface. at both spring sites, the calcareous deposits were not A limited number of studies have monitored fluores- significantly large enough due to the limited measur- cent intensities using long interval measurements with ing period. Therefore, the influence of the purgation a flow-through fluorometer. Fluorescent intensity on the fluorescence measurement was assumed to be changes were first observed in 1999 using synchronous insignificant and a correction analysis for the purga- scans of fluorescent spectra in water samples taken by tion was neglected. chance prior to and after a strong earthquake (Bal- The optical system consists of four different LEDs. derer and Leuenberger, 2007,Grant,R.A., T.Halliday, Each light source has a specific wavelength. In this case W.P. Balderer, F. Leuenberger, M. Newcomer, G. Cyr, 370 nm, 470 nm, 525 nm and 660 nm were used to F.T. Freund. 2011,Fidaniet al., 2017.Our studyisone excite the fluorescent components in the water. The of the first to monitor fluorescent intensities over a emission optics are arranged perpendicular to the excita- time of 11 weeks in two different springs in the north- tion plains. The emissions of the fluorophores are ern part of Switzerland. Changes in fluorescent inten- filtered to determine the wavelength range detected by sities are correlated in our study with the seismic data photodiodes (Schnegg, 2002). The monitored measure- of nearby stations to deduce potential coincidences. ment interval of the fluorescence intensity in mV was The method of fluorescent monitoring used in our 300 s. The schematic concept of the fluorometer is study and the geological and tectonic setting of our shown in Fig. 1. chosen physical area in Baden and Rheinfelden A high turbidity (mainly caused by degassing) can Switzerland are explained. Subsequently, the results adversely influence the intensity of the fluorescent are presented, discussed and conclusions about the measurements. In the case of the Rheinfelden spring method are drawn. where a high CO content exists, a degassing device was Fig. 1 Schematic functional sketch of the installed flow-through fluorometer of the type GUGN – FL30. The light sources with the specific wavelengths namely, 370 nm, 470 nm, 525 nm and 660 nm and corresponding detector ends are represented together with arrows perpendicular to the main water through flow tube (modified after Schnegg 2002) Mäder et al. Geoenvironmental Disasters (2018) 5:9 Page 3 of 9 installed to reduce turbidity. Besides degassing and (Muschelkalk and Keuper) from the early Mesozoic era turbidity, a possible mixing of the thermal spring water (Burger, 2009). Rheinfelden is situated in close vicinity to with a neighbouring aquifer can influence the fluores- the Rhine Graben-structure, a 300–350 km long rift where cence signal. The order of magnitude by which the the geology and tectonics have been studied in detail (Sis- fluorescence intensity is affected by such a mixing de- singh, 1998;Becker, 2000;Ustaszewski and Schmid, 2007). pends on the constituents of the inflowing aquifer. An- The detailed well profile of the Rheinfelden spring is pre- thropogenic influxes in the form of chemicals such as sented by Ryf (1984). cleaning agents from nearby industry or thermal baths The thermal springs of Baden lie in the “Lägeren”– resorts could also adversely influence measurements structure where the Limmat eroded into the Muschelkalk taken. layers in the eastern part of the Faltenjura. The Baden hot spring contains fluids originating from the base rock Geological and tectonic setting of the ascending through the evaporites of the middle investigated springs of Baden and Rheinfelden Muschelkalk layers, along a tectonic fault, which is The measurements presented here originate from an characterized as the Jura-Overthrust (Burger, 2009; unused thermal deep well at Rheinfelden (latitude Löw, 1987;Nagra, 2014,Fig. 3.3–2). The aquifer has 47.5505°, longitude 7.8058°) and from a hot spring in a piezometric head of 359 m a.s.l. and is therefore ar- Baden (latitude 47.4808°, longitude 8.3130°). The geo- tesian against the local river Limmat (350 m a.s.l.) logical overview of Switzerland is presented in Fig. 2 and the surrounding groundwater streams (348– whereas the tectonic setting and the seismicity of the in- 357 m a.s.l.) (Löw, 1987). The Baden spring water vestigated area are presented in Fig. 3. with a total mineralization of around 4.5 g/l and a The Rheinfelden thermal well temperature is 12 °C conductivity of 5970 μS/cm and is hydro-chemically with a pH of 6.6 and a conductivity of 5420 μS/cm. characterized by Na-Ca-(Mg)-Cl- SO type and con- This well contains Na-Ca-Cl-HCO -SO thermal tains higher amounts of characteristic dissolved gas- 3 4 water with a high CO content and originates at a ses, namely H S(3.0mg/l),CH (< 0.3 mg/l) and 2 2 4 depth of 550 m. Geologically it is in late Palaeozoic sedi- CO (292 mg/l) (Rick, 2007;Högl, 1980). The water ments (Perm, Rotliegendes) below dense evaporitic layers has a temperature around 46 °C and a pH of 6.6. Fig. 2 Geological Map Switzerland and the bordering countries of France and Germany. Switzerland is high-lighted in green on the map of Europe on the right side. The size of the geological map of Switzerland including the four main distinctive units namely, Faltenjura (blue), Molassebecken (yellow), Helvetikum (green) and Kristallin (pink, including the Aar-Massiv, bright-red) is illustrated on the left side. The two Fluorescence monitoring locations Rheinfelden (R) and Baden(B) are presented by bold black dots (modified after swisstopo, BWG). Mäder et al. Geoenvironmental Disasters (2018) 5:9 Page 4 of 9 Fig. 3 Map of the area of Northern Switzerland and the bordering countries of France and Germany with represented magnitudes of the main occurring earthquakes. The two Fluorescence monitoring locations Rheinfelden (R) and Baden (B) are indicated with bold blackish dots. The reddish lines represent the main tectonic faults in the nearby area of the measurement locations. The greyish circles illustrate the locations of the registered earthquakes since 2001. The size of the circles corresponds to the magnitude of the earthquakes according to the legend on the right side of the figure (modified after SED) Fig. 4 Diagram of the monitored Fluorescence intensity of the thermal water in Baden (B) over the measuring period. The fluorescence intensity at wavelength 470 nm is presented in the blueish curve whereas the greyish curve presents the fluorescence intensity at 525 nm. The orange squares depict the registered earthquakes with the location and the magnitude in brackets. The earthquakes are scaled depending on their precursor manifestation zone, which was calculated by Eq. 1 Mäder et al. Geoenvironmental Disasters (2018) 5:9 Page 5 of 9 Fig. 5 Diagram of the monitored Fluorescence intensity of the thermal water in Rheinfelden (R) over the measuring period. The fluorescence intensity at wavelength 470 nm is presented in the blueish curve whereas the greyish curve presents the fluorescence intensity at 525 nm. The orange squares depict the registered earthquakes with the location and the magnitude in brackets. The earthquake close to Albstadt (E3) does not appear on the figure because of the distance between the measurement location and the epicenter, which exceeded 100 km. The earthquakes are scaled depending on their precursor manifestation zone, which was calculated by Eq. 1. The blackish – dashed line marks the interruption of the measurement because of the loss of power supply Results approach assumes that non-mechanical precursors are The following figures (Figs. 4 and 5) show fluorescent caused by deformation of the surrounding medium. intensities over the measured time and the location and The theory states that a possible manifestation of a magnitude of the earthquakes that occurred. Only precursor occurs within the strain radius and can be earthquakes which had a magnitude 1 or higher and detected when the monitoring site lies inside this were experienced within a radius of 100 km from the estimated zone. The calculation of the strain combines spring site measurement location were considered. Out the impact of the magnitude and the distance to the of the four possible wavelength sensors only the most monitoring site. This result helps predict if a precursor significant results are presented. These were using the is expected at the measurement site or not. According 470 nm and 525 nm signals. The strain (ε) and strain to Dobrovolsky et al. (1979) lies the monitoring side radius of the nearby registered earthquakes are calcu- inside the deformation zone if the determined strain is − 8 lated using the Dobrovolsky relation (Eqs. 1 and 2) above 10 . However, whether the monitoring site lies (Dobrovolsky et al., 1979). inside the strain radius is not that significant when the expected changes in fluorescence intensities are assumed 0:43M 10 ¼ strain radius ð1Þ to be caused through the stress activated charge carriers. It has been demonstrated in lab experiments that these 1:3M−8:19 charge carriers are highly mobile and it is assumed that 10 ¼ ε ð2Þ they can propagate far away from the stressed rock region (Freund and Freund, 2015; Scoville et al., 2015). The strain radius is the estimated zone around the Nevertheless, the strain and the strain radius were epicentre of an effective manifestation of precursor calculated to follow the initial scaling approach of earth- deformation and is dependent on the magnitude M of quake precursors and to get a rough estimation of the the earthquake (Dobrovolsky et al. 1979). This relation is extent of the deformation zone. The positive holes are a very useful approach to obtain a semi-quantitative generated in the deformation zone and therefore it is number for the precursor manifestation zone. This expected that stronger earthquakes with larger Mäder et al. Geoenvironmental Disasters (2018) 5:9 Page 6 of 9 Table 1 The registered earthquakes during the measuring period with a magnitude higher than 2.0 are listed below with the corresponding geographical coordinates (Lat / Long), magnitude (M) and depth of the earthquakes. E1, E2, E3, E4 are identification numbers for the earthquakes which are mapped in Figs. 4, 5 and 6. The distances between the epicentres and the measurement locations Baden (B) and Rheinfelden (R) were calculated. The strain radius was calculated by means of Eq. 1. Strains at the monitoring site R and B are calculated by Eq. 2 Earthquake Lat / Lon [°] M Depth [km] Distance to B [km] Distance to R [km] Strain radius [km] Strain ε at: B Strain ε at: R −11 −11 E1 46.90 / 7.42 2.6 5.7 93.3 77.9 13.1 1.91*10 3.28*10 −12 −11 E2 47.15 / 7.15 2.4 9.8 95.0 66.5 10.8 9.93*10 2.89*10 −11 − 11 E3 48.24 / 9.05 2.5 9.6 100.0 > 100 11.9 1.15*10 < 1.15*10 −11 − 11 E4 47.66 / 8.74 2.2 7.4 37.7 71.0 8.8 8.73*10 1.31*10 deformation zones tend to activate more charge carriers mainly caused by short intervals of high CO overpres- than weaker ones. Therefore, only earthquakes with sure and outgassing. The reason behind is the thermal magnitude higher than 2.0 were considered for the strain water of the Baden spring is CO oversaturated and respectively strain radius calculations and as possible outgases through pressure decrease with the natural detection targets. The four registered earthquakes with a ascendance of the water. This outgassing process does magnitude higher than 2.0 are listed in Table 1 and not happen continuously. It is more a periodical process. mapped in Fig. 6. Data and information about registered The measured course of fluorescent signal at 470 nm earthquakes are provided from the SED (Swiss Seismo- shows one gradual increase (April 23th 2015 – May 4th, logical Service). 2015) of more than 1 mV which is followed by a signifi- cant rapid drop. The other obvious event is a significant Results: Baden jump in intensity to 8 mV within 3 days and followed by The measured fluorescence intensity at wavelength of a wide fluctuation until a significant rapid drop occurred 470 nm which is shown in Fig. 4 fluctuated widely (June 1st, 2015). The fluorescence intensity at wavelength around 4 mV whereas the intensity at wavelength of 525 nm shows a similar but not identical behaviour as the 525 nm fluctuated around 2 mV. The measurements signal at 470 nm. During the survey, many smaller sometimes showed dispersions in the fluorescent inten- earthquakes within a radius of 100 km happened. The sity within a small-time interval. These events were earthquakes close to Bern (E1) with a magnitude of 2.6 Fig. 6 Map of Switzerland with representation of all the earthquakes, which were registered within a time span of 90 days before the fluorescence monitoring was stopped are highlighted in the map of Switzerland by yellow dots. The size of the circles corresponds to the magnitude of the earthquakes according to the legend on the right side. The location of the earthquakes from Table 1 are highlighted with the blackish arrows. The measurement locations Baden (B) and Rheinfelden (R) are indicated by the bolt blackish dots (modified after SED) Mäder et al. Geoenvironmental Disasters (2018) 5:9 Page 7 of 9 and Albstadt (E3) with magnitude 2.5 were the strongest rock regions. When more charge carriers are generated, but both epicentres were relatively far (E1: 93.3 km, E3: the oxidation on the rock–water boundary is increased 100.0 km) from the measuring station (B) (Table 1,Fig. 6). and the fluorescence intensity rises. The expected shape The seismic event E1 was the strongest earthquake with a and the duration of the increasing fluorescence intensity corresponding strain radius of 13.1 km. The earthquake curve prior to an earthquake is not known yet but it is from May 31th 2015 around Andelfingen (E4) with mag- assumed that it is most likely variable. nitude 2.2 lay just 37.7 km away from the station B and is The theory assumes that the higher the magnitude of therefore of most interest for our studies. All calculated an earthquake is, the higher the impact of the fluores- strains at monitoring site B are below the threshold of 10 cent signal in the measured groundwater will be. and lie therefore outside the deformation zone. Because of the lack of strong seismicity in close vicinity to the monitoring stations during the measuring period Results: Rheinfelden it is difficult to determine correlations between changes The monitored fluorescence intensity curves of Rhein- in fluorescence and earthquakes. felden, measured at wavelengths 470 nm and 525 nm The calculated strains of the earthquakes E1 – E4 for are presented in Fig. 5. The intensity at 470 nm fluctu- both monitoring sites are much smaller than the postu- − 8 ated widely with a range from 1.6 mV to 4.1 mV. The lated 10 . This means that these four earthquakes fluorescence signal at 525 nm shows an almost identical should not manifest themselves at the monitoring site behaviour as the signal at 470 nm but with lower fluor- using the Dobrovolsky approach. However, all the four escent intensities. Despite an installed outgassing earthquakes (E1 – E4) happened at very shallow depths device, the very high CO content of the Rheinfelden and it should be considered that the stress generated spring caused a greater dispersion of the signals than in charge carriers can flow much further than the strain the Baden measurements. The beginning of the meas- radius estimates. uring period is dominated by a rapid increase from At the Rheinfelden spring site the fluorescence signal 1.8mVto4.1 mV with twomain rapid drops, which steadily increased until the earthquake (E1) with a interrupts the gradual increase in fluorescence intensity magnitude of 2.6 close to Bern happened. Subsequently at 470 nm. Another significant drop (April 24th, 2015) the fluorescence intensity rapidly dropped after the happened due to a sudden power loss to the registered earthquake. However, this phenomenon fluorometer which is indicated through the blackish – cannot be clearly identified as a coherence between the dashed line in Fig. 5. This sudden drop in fluorescence fluorescence signal and the earthquake because of the intensity at both wavelengths occurred because of the low magnitude and the large distance to the measuring shut-down (power loss) of the fluorometer and must be station (R). Additionally, on April 11th, 2015 a similar negated for interpretation. After this interruption, the rapid drop in fluorescence intensity occurred but in continuation shows a considerable steady increase at absence of an earthquake. The registered earthquakes both distinctive wavelengths until a sudden drop (May close to Biel (E2) and Albstadt (E3) do not show any 18th, 2015) occurred. The last parts of the curve are possible changes to the fluorescence signals at both dominated by two rapid increases, both of which are spring sites. The earthquake E3 is not reflected in Fig. 5 followed by rapid drops (Fig. 6). Out of the 4 earth- because of the distance, which exceeded the maximum quakes from Table 1, the earthquake close to Biel (E2) distance of 100 km. with a magnitude of 2.4 and a corresponding strain Prior to the earthquake (E4) with a magnitude of 2.2 radius of 10.8 km was the closest earthquake (66.5 km) close to Andelfingen, an increase in fluorescence inten- to the Rheinfelden measurement location (R). However, sity was measured at both spring sites. Moreover, the all the strains at monitoring site R lie below the postu- fluorescence signals suddenly dropped immediately after lated threshold. the earthquake (E4) occurred. The increase and sudden decrease of the fluorescence intensity was more pro- Discussion nounced at the Baden spring (B) than in Rheinfelden The fluorescence intensities vary at moderate magni- (R). The reason behind this could be found in the tudes at both spring sites over the whole monitoring shorter distance from the epicentre to the measuring period. Intervals with stable intensity values are scarce. station in Baden compared to the distance to Rheinfel- The main trend of the observed fluorescence monitoring den. This recorded specific change in fluorescence is dominated by several increases which are followed by intensity is quite remarkable because of its occurrence at sudden decreases in fluorescent intensities. both spring sites prior to and after the earthquake. Such Intensified tectonic stresses in the subsurface leads to an event in fluorescence change would be expected and an increase of stress generated charge carriers which would be consistent with the theory of the release of flow out of the stressed rock region into the less stressed stress generated charge carriers which cause an oxidation Mäder et al. Geoenvironmental Disasters (2018) 5:9 Page 8 of 9 of the groundwater. However, that this change in the the Dobrovolsky relation〖10〗^(0.43*M) strain radius of the nearby registered earthquakes are calculated using the Dobrovolsky relation fluorescence signal can be identified because of increased and diminished tectonic stresses in the subsurface is Acknowledgements beyond the current understanding of the phenomena. Very special thanks goes out to Mr. Kost and the RehaClinic team Baden and to Mr. Franz Resnig, Thermal spa foundation. Dr. Barbara Reyes-Trüssel, Nevertheless, this method could be a useful tool in future Geophysicist at EBERHARD & Partner AG for providing the possibility to use earthquake forecast because of its sensitivity to a wide the deep borehole at Rheinfelden for on-line measurements, Mr. Lehman catchment area which depends on the extent of the and the city of Rheinfelden for the support they provided us during the survey. aquifer and its flowrate. Furthermore, the modest method- ology and the straightforward installation and mainten- Funding ance of the fluorometer is another point in favour of this This published research was not subject of any special funding and results from the normal program of education studies of ETH in the frame of Earth monitoring method. The limitation of the method lies in Science Department. The applied instruments are property of the Geological the strong influence of outgassing and turbidity on the Institute, Engineering Geology and of the hydrological section of the Swiss fluorescence signal of the groundwater. External factors Federal Institute for Forest. which influence the fluorescence intensity besides aquifer Availability of data and materials mixing and anthropogenic influxes are not yet known and The fluorescence datasets supporting the conclusions of this article are further research is needed. included within the article. The information on the registered earthquakes is available in the repository of the SED: http://www.seismo.ethz.ch The information on the flow-through fluorometer is available on: http:// Conclusion www.albillia.com The results presented clearly show the variability of Authors’ contributions fluorescence intensity of ground water at the distinct Dr. WB was as Senior lecturer supervisor of the presented study and Co- wavelengths. Furthermore, the results support a possible Author and organized the availability of investigated test sites, setup of instruments, instruction of maintenance and exploitation and interpretation link between the stress generated charge carriers caused of fluorescence monitoring. MM made the fluorometer measurements by tectonic processes leading to earthquakes and their exploitation, and interpretation of the results and studied the relation to the interaction with the investigated thermal water. However, occurring earthquakes of the related areas in the frame of his thesis of Bachelor of Earth Sciences degree from ETH Zurich. Dr. FL was responsible these preliminary results should be confirmed by further for the lab measurements and the fluorescence synchronous scan spectra monitoring of fluorescence of groundwater at alternate measurements on additional water samples of both investigated thermal groundwater sites in tectonically more active areas. water monitoring sites. All authors read and approved the final manuscript. The selection of appropriate springs or wells is crucial. Authors’ information Most suited for in-situ fluorescence monitoring are sites Werner Balderer was from 1986 to 2010 Lecturer of Isotope Hydrogeology, with artesian groundwater outflow such as the investi- and General Hydrogeology at ETH Zurich, his research interests include Mineral and Thermal water and research on Natural fluorescence of gated Baden spring and the Rheinfelden borehole. groundwater as proxi of tectonic activity. Groundwater of pumped wells are more affected by Matthias Mäder holds a Bachelor of Earth Sciences degree from ETH Zurich disturbances due to pumping intervals and non-steady with a major in geophysics. Matthias is a current Master student in Petroleum Engineering & Geosciences state situations in respect to considering hydraulic head at TU Delft, Netherlands. His research interests includes the understanding of and degassing processes. pre-earthquake phenomena and petroleum geology. Furthermore, the monitoring period should be ex- Ethics approval and consent to participate tended to enhance the probability of earthquake occur- ‘Not applicable’. rences and to allow long term analysis. Fluorometers with a wider wavelength spectrum and an advanced sen- Consent for publication According to the ETH Zurich the bachelor thesis and its publication belongs sitivity would be a further asset. This would allow the to the personal property right of the students of Bachelor degree from ETH wavelength spectrum to be tuned to the most signifi- Zurich. cant wavelengths in terms of changes in fluorescent Competing interests intensities as an earthquake precursor. Furthermore, a All the authors have no competing interests in the research subject of this wider wavelength spectrum could provide further publication. No one is working in industries or has ties to such in the information about possible shifts in fluorescence domain of the published research. Therefore, no financial and non-financial competing interests exist. spectra. Beyond that, further investigations into the oxidation process of dissolved organic compounds in Publisher’sNote the ground water should be done in order to improve Springer Nature remains neutral with regard to jurisdictional claims in the understanding of the phenomena. published maps and institutional affiliations. Abbreviations Author details B: Measuring station in Baden; E1 -E4: Earthquake identification numbers; Department of Geoscience, TU Delft, Stevinweg 1, 2628 CN Delft, GUGN-FL30: type of fluorometer developed by the University of Neuchatel; Netherlands. Geological Institute, Engineering Geology, ETH Zürich, LED: Light emitting diode; M: Magnitude; R: Measuring station in Sonneggstrasse 5, 8092 Zürich, Switzerland. Geological Institute, ETH Zürich, Rheinfelden; ε: strain of the nearby registered earthquakes calculated using Sonneggstrasse 5, 8092 Zürich, Switzerland. Mäder et al. 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Journal

Geoenvironmental DisastersSpringer Journals

Published: Dec 1, 2018

Keywords: Environment, general; Earth Sciences, general; Geography, general; Geoecology/Natural Processes; Natural Hazards; Environmental Science and Engineering

References