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the Creative Commons Attribution 4.0 License.
| 20 Dec 2024
Gypsum as a potential tracer of earthquake: a case study of the Mw7.8 earthquake in the East Anatolian Fault Zone, southeastern Turkey
Abstract. Obvious macroscopic anomalies of geothermal fluids were observed before and after the Mw 7.8 earthquake in Turkey. In order to find out the relationship between geothermal fluid anomalies and earthquakes, we performed a systematic hydrogeochemistry and isotopic analysis of the geothermal fluids in the East Anatolian Fault Zone (EAFZ). The results show that these geothermal fluids were reconstructed (including: energy and materials) by earthquakes. Based on chlorine – enthalpy model, the temperature of the deep geothermal fluid has been increasing to 382 °C on the strength of the energy released by the seismic activity. However, the information of the deep geothermal fluid was eventually covered due to the infiltration of a large amount of shallow cold water after the earthquake. The abnormal concentrations of Ca2+ (54.04~501.58 mg/L), Mg2+ (6.58~116.20 mg/L), SO42– (6.37~287.74 mg/L), Sr (34.78~3244.8 μg/L), and Ba (1.89~196.48 μg/L) in geothermal water shown that the geothermal water has undergone complex water-rock interaction processes such as gypsum, calcite, dolomite, anorthite and serpentinization. Specially, significant gypsum dissolution was observed at HS05, HS09 and HS14 before and after the earthquake, suggesting that the earthquake broke the balance of water-rock reaction and promoted the dissolution of gypsum. Combined with geological background and previous studies, we propose that shallow sedimentary minerals, such as gypsum, have the potential to be used as earthquake warning indicators. However, shallow minerals are controlled by many external factors (e.g., temperature, pressure, climatic conditions, seasonal changes etc.), which greatly weakens their practical value in earthquake early warning.
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CC1: 'Comment on hess-2024-395', Giovanni Martinelli, 03 Jan 2025
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I found useful and interesting the manuscript https://doi.org/10.5194/hess-2024-395 submitted by Luo et al. Significant geochemical anomalies in geothermal fluids were detected before to and during the Mw 7.8 earthquake in Turkey. To investigate the correlation between geothermal fluid abnormalities and seismic events, the authors conducted a comprehensive analysis of hydrogeochemical and isotopic study of geothermal fluids in the East Anatolian Fault Zone. The findings indicate that these geothermal fluids were affected by seismic activity. According to the chlorine-enthalpy model, the temperature of the deep geothermal fluid significantly rose. However, the data regarding the deep geothermal fluid was eventually affected by the influx of significant amounts of superficial cold water following the earthquake. The anomalous levels of Ca, Mg, SO4, Sr, and Ba in geothermal water indicate that the water has experienced complex water-rock interaction processes, including gypsum, calcite, dolomite, anorthite, and possible serpentinization. Substantial gypsum dissolution was noted at locations HS05, HS09, and HS14 both before to and during the earthquake, indicating that the earthquake favoured the dissolving of gypsum. The authors suggest that superficial sedimentary minerals, including gypsum, may serve as markers for earthquake warnings. During earthquakes, alterations in geochemical conditions result in variations in gypsum solubility, subsequently causing anomalous amounts of SO4, Ca, Sr, and Ba in geothermal water. The solubility of gypsum is influenced by several environmental variables, including meteorological conditions and seasonal variations, hence reducing its practical use for earthquake early warning systems. I think the paper is well organized but I found the possible lack of some sentences devoted to the mechanism of the observed upsetting. Redox conditions have been affected? Deep originated CO2 could be suspected as an eventual carrier of H2S? The addition of some comments about the listed topics could possibly help readers to better understand during the tectonically active period. I hope the paper will be soon accepted and published after some minor revisions.
Citation: https://doi.org/10.5194/hess-2024-395-CC1 -
AC1: 'Reply on CC1', Zebin Luo, 05 Jan 2025
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Dear Giovanni Martinelli
Thank you for your recognition of our work and valuable suggestions, which are very helpful for us to improve the quality of our manuscripts. Your two comments are exactly where we are lacking. At your suggestion, we plan to add a subsection to the discussion section for assessing the contribution of mantle degassing to EAFZ geothermal fluids. The supplementary content is as follows:
Contribution of Mantle Degassing to EAFZ Geothermal Fluids
Mantle degassing occurs extensively along fault zones, and the amount of volatile release can sometimes be comparable to the degassing associated with volcanic activity e.g. (Fischer and Aiuppa, 2020; Zhang et al., 2021). Sulfur-containing volatiles (such as SO₂ and H₂S) ascend along these fault zones and, upon reaching the shallow subsurface, mix with groundwater, where they are oxidized and migrate in the form of SO₄2- in geothermal fluids. Therefore, the contribution of mantle degassing to the SO₄2- content in geothermal fluids cannot be overlooked. To better assess the contribution of mantle degassing to SO₄ in EAFZ geothermal fluids, we need to consider the sources and modifications of geothermal fluids.
The deep-origin geothermal fluids in EAFZ are significantly diluted by shallow groundwater, masking the chemical signature of deeper fluid components. This dilution process introduces a large amount of dissolved oxygen, which facilitates the oxidation of H₂S to SO₄2-. Lacking O₂ was detected in EAFZ geothermal gases suggested that the dissolved oxygen may have been consumed (Italiano et al., 2013; Yuce et al., 2014). However, it is important to note that H₂S, H₂, and CH₄ can all react with oxygen. Thermodynamic calculations indicate that CH₄ is more favorable than H₂S in oxidation reactions (ΔG° CH4 = -818.1 kJ/mol, ΔG° H2S = -494.2 kJ/mol, at 298 K and 1atm). In actual geothermal systems, however, the depletion of H₂S is more commonly observed than the depletion of CH₄, suggesting that H₂S may be oxidized before CH₄. To resolve this apparent contradiction, we propose the following possible explanations: 1) Oxidation of H₂S: While thermodynamic calculations predict CH₄ oxidation first, a small amount of H₂S might still be oxidized simultaneously with CH₄. Due to the much lower concentration of H₂S in geothermal systems compared to CH₄, H₂S is consumed more quickly, leaving CH₄ with a higher residual concentration. 2) Exogenous CH₄ Supply: In addition to mantle-derived CH₄, other sources of CH₄, such as biogenic CH₄ and thermogenic CH₄ (e.g., serpentinization), may contribute to the geothermal system. These external sources could increase the concentration of CH₄ in the geothermal fluids.
In the EAFZ, we observed significant contributions of biogenic and serpentinization-derived CH₄ but did not detect significant levels of H₂S (Italiano et al., 2013; Yuce et al., 2014). Therefore, we proposed that although H₂S may contribute to the geothermal system, its impact is likely limited due to its relatively low concentration. Inversely, the notable increase in SO₄2- concentrations following seismic events is likely primarily controlled by the dissolution of shallow evaporitic layers (such as gypsum). All in all, while the oxidation of H₂S may contribute to SO₄2- formation, distinguishing between H₂S oxidation and sulfate dissolution requires additional geochemical indicators, such as S isotopes and Ca isotopes, for more accurate assessments.
References
Fischer, T. P. and Aiuppa, A.: AGU Centennial Grand Challenge: Volcanoes and Deep Carbon Global CO<sub>2</sub> Emissions From Subaerial Volcanism-Recent Progress and Future Challenges, Geochemistry Geophysics Geosystems, 21, 2020.
Italiano, F., Sasmaz, A., Yuce, G., and Okan, O. O.: Thermal fluids along the East Anatolian Fault Zone (EAFZ): Geochemical features and relationships with the tectonic setting, Chemical Geology, 339, 103-114, 2013.
Yuce, G., Italiano, F., D'Alessandro, W., Yalcin, T. H., Yasin, D. U., Gulbay, A. H., Ozyurt, N. N., Rojay, B., Karabacak, V., Bellomo, S., Brusca, L., Yang, T., Fu, C. C., Lai, C. W., Ozacar, A., and Walia, V.: Origin and interactions of fluids circulating over the Amik Basin (Hatay, Turkey) and relationships with the hydrologic, geologic and tectonic settings, Chemical Geology, 388, 23-39, 2014.
Zhang, M., Xu, S., Zhou, X., Caracausi, A., Sano, Y., Guo, Z., Zheng, G., Lang, Y.-C., and Liu, C.-Q.: Deciphering a mantle degassing transect related with India-Asia continental convergence from the perspective of volatile origin and outgassing, Geochimica Et Cosmochimica Acta, 310, 61-78, 2021.
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CC2: 'Reply on AC1', Giovanni Martinelli, 06 Jan 2025
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OK, I agree with your updates and hope the paper will be soon accepted and published.
Citation: https://doi.org/10.5194/hess-2024-395-CC2 -
AC2: 'Reply on CC2', Zebin Luo, 06 Jan 2025
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Thank you very much for your valuable Suggestions.
Citation: https://doi.org/10.5194/hess-2024-395-AC2
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AC2: 'Reply on CC2', Zebin Luo, 06 Jan 2025
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CC2: 'Reply on AC1', Giovanni Martinelli, 06 Jan 2025
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AC1: 'Reply on CC1', Zebin Luo, 05 Jan 2025
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RC1: 'Comment on hess-2024-395', Walter D'Alessandro, 13 Jan 2025
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The manuscript “Gypsum as a potential tracer of earthquake: a case study of the Mw7.8 earthquake in the East Anatolian Fault Zone, southeastern Turkey” by Luo et al. presents the results of sampling campaign of groundwaters in the area of the two strong earthquakes that hit heavily Turkey in February 2023. Only the analytical results (major ions, trace elements and water isotopes) of samples collected about one year after the quakes are considered, which is a strong limitation of this study. I feel that this study cannot be published in this form.
Major comments:
Lines 33-36 (abstract): This is one of the most critical claims made by the authors. “Specially, significant gypsum dissolution was observed at HS05, HS09 and HS14 before and after the earthquake, suggesting that the earthquake broke the balance of water-rock reaction and promoted the dissolution of gypsum.” In the paper only the results of the analyses of the samples taken one year after the earthquakes are discussed. How should it be possible to evidence variations “before and after the earthquake” if only one sample was taken?
Line 124: The authors should explain on which basis the 16 sampling sites have been chosen.
Line 124: the authors claim to have sampled hot springs but with the exception of the peculiar hyperalkaline spring HS15, which derive its increased temperature from deep circulation, no other sample could be called “hot”. Furthermore, I would not define a well with water at 24 °C as geothermal well. Actually, in the results (line 144) the authors affirm that temperatures of the sampled waters are low.
The methodological section has many limitations:
Lines 130-131: it is unclear if filtration has been made in the field and before acidifying the aliquot for cation analysis. Please specify
Line 131: MAT 253 is a model, please specify the used technique
Line 133: please specify the analysed species and the relative reproducibility and detection limits?
Line 136: please specify the analysed trace elements and the relative reproducibility and detection limits?
In the results the authors claim often that some element or ionic species is increased (sometimes adding obviously) but they do not specify with respect to what. Maybe they intend that the concentrations are high.
In the same section they speak of geothermal water but they do not present any evidence that these are geothermal waters.
The discussion about the geothermal fluids has great limitations.
The authors do not present evidences that the sampled waters are, at least partially, fed by hydrothermal systems. The fact that in the area some geothermal system has been discovered and studied, does not mean that all groundwater samples taken in the area are fed by them. The temperatures of the collected samples are low and, as highlighted by the binary diagram of fig. 3 and the ternary diagram of fig. 4, their compositions do not reflect high temperature interactions with the rocks. Also the silica geothermometers show low temperatures considering that for such systems equilibrium with chalcedony (or even christobalite or amorphous silica) should be taken into consideration.
Especially the use of the mixing models has been made in the wrong way. Mixing models can be applied only to water samples that belong to the same system and not to water samples collected tens of km away from each other and for which no connection has been demonstrated.
The estimation of temperature for the “deep geothermal fluid” (please define) of 382 °C is absolutely unreliable. The sample was taken, as shown in the second video in the supporting information, from an artesian well (although in table 1 it is classified as spring). I think it is impossible that an artesian well, whose upflow is generally rapid, would have only 15 °C temperature if even only a small part of the water would come from a geothermal system with 382 °C.
The discussion about the sulfate anomalies is highly confusing. Many points are unclear or wrong.
Why are only samples HS05, HS09 and HS14 considered anomalous? HS01, HS03 and HS04 have also elevated sulfate values.
Why should these high sulfate values be considered anomalous and induced by the earthquake? Sulfate dissolution from evaporite deposits within the aquifers is an ubiquitous process independent from seismic activity.
Why do the authors use these low averages for Ca (55.23 mg/L) and SO4 (8.31 mg/L) concentrations before earthquake? Baba et al. (2019) in their paper report concentrations up to 773.56 mg/L for Ca and up to 1287.24 mg/L for SO4 much higher than in the samples collected for this study.
Finally, the authors indicate the whitening and turbidity of the water in a sample as verification for the sulfate anomaly. But without analysis there is no possibility to affirm that such visual anomaly was due to gypsum dissolution.
Furthermore, the authors mistake the samples. The site with the high sulfate concentration is HS14, while the site to which the pictures of figure S1 and of video 01 refer is HS15 which has the lowest sulfate value (1.21 mg/L).
Lines 388-389: The authors presenting the data of a single sampling campaign have no evidence to affirm that “the geothermal fluid was diluted due to the infiltration of a large amount of shallow cold water after the double earthquakes in February 2023”.
Minor comments
Line 22: What do the authors mean with “systematic” which do not appear only in the abstract but has been repeated many times in the whole text?
Lines 24 and 25: The meaning of the sentence is obscure (reconstructed by earthquake?)
Line 29: the authors use often the term “abnormal” but they do never define with respect to what.
Line 38: please define “shallow minerals”.
Line 61: which evidence have the authors of a “geothermal fluids circulation”
Line 69: please define the “geothermal fluid anomaly index”
Lines 70-71: the subject is missing in this sentence.
Line 82: please define what a “tectonic collage” is.
Fig. 1a: altitude scale is missing.
Line 105: probably crystalline instead of crystallization.
Line 145: in table 1 HS15 is considered a spring, which one is correct?
Line 146: the authors claim that ”the closer to the epicenter, the higher the SiO2 content”, which makes no sense. Firstly because the earthquakes were two and only one sample close to one of the epicenters has a higher SiO2 value. Moreover, other two sampling points with low to very low SiO2 concentrations have the same position as the “anomalous” one.
Lines 154-156: the sentence “The δ18O and δD of samples varied from –11.30‰ to –6.55‰ and –65.43‰ to –34.43‰ respectively, which is near to the global meteoric water line (GMWL) (Craig, 1961) (Fig. 3), suggesting their meteoric water origin” has no sense. The regression line obtained plotting both δ18O and δD values in a graph can be close to GMWL.
Line 159: what type of Statistical analysis?
Line 160: please define “fluid activity elements”.
Line 161: I do not understand what the authors mean with “are at historic highs versus”. If the authors mean that the concentrations are higher than in the past, then the fig. S2 does not prove nothing. Al and Ba are below the median value of the literature data while the remaining are around the median value not showing particularly high values. Furthermore, it is unclear which data are compared in fig. S2 with the present data.
Table 1: please indicate the coordinates with at least 4 digits after the comma, with only two digits it’s impossible to obtain a reliable position. Looking at Fig. 1, the indicated coordinates of HS05 are clearly wrong.
Line 190: the highest values do not belong to samples collected closer to the sea.
Line 190: δ18O and δD values are inverted.
Line 212: magma mixing with geothermal fluids generally end in a volcanic explosion which is not the case here.
Lines 224-225: the sampling sites are tens of km far from the Mediterranean coastline, how and why should they be “obviously contaminated by Mediterranean Sea water”?
Line 226: which previous study? Please add a reference.
Line 233: pollution is a term connected to an anthropogenic origin, so please use the term contamination instead.
Lines 233-236: I do not understand the meaning of this sentence.
Lines 290-292: the two processes are not alternative. Serpentinization includes secondary minerals precipitation.
Finally, I would signal a possible conflict of interest being the handling editor of the same institution of one the corresponding author.
Citation: https://doi.org/10.5194/hess-2024-395-RC1 -
CC3: 'Comment on hess-2024-395', Hafidha Khebizi, 17 Jan 2025
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Dear authors and colleagues of the scientific community,
I congratulate the authors for their interesting work entitled Gypsum as a potential tracer of Earthquakes: a case study of the Mw7.8 2 earthquake in the East Anatolian Fault Zone, southeastern Turkey, and I hope it will be published soon. To find out the relationship between geothermal fluid anomalies and earthquakes, the authors performed a systematic hydrogeochemistry and isotopic analysis of the geothermal fluids in the East Anatolian Fault Zone (EAFZ). The results show that earthquakes reconstructed these geothermal fluids.
Considering gypsum as an earthquake tracer is excellent reasoning for analysing the impact of anomalies after the earthquake, and the work could be a great reference for future studies related to the earthquake.
To enrich this excellent analysis, I have some remarks concerning the implication of macroscopic and microscopic aspects of geothermal fluids before and after the earthquake, notably the relation with the structural geology of the region. For this, some questions seem important to be asked.
First, from a macroscopic point of view, it is necessary to understand, in the normal case (before the earthquake), from a geological point of view, if the existing deformations (faults) already have effective structures for the infiltration of meteorological waters and the implication of the disposition of the thermal springers according to the faults. After the earthquake, is there any sampling from Miocene groundwater and soil? Is there recent salt precipitation in the Miocene and upper Eocene-Oligocene soil and/or in the soil of the surrounding springer sources? Is there a rise in the ground level due to fault action, and are there marine intrusions that occurred after the strike-slip? Is there significant contamination of the water table (increased electrical conductivity)?
From a microscopic point of view, gypsum is easily and quickly influenced by contact with water, thanks to its physicochemical characteristics, in particular its very high dissolution rate and its solubility in water that make it an excellent tracer of hydrochemical anomaly but also a tracer of lithological instability (Khebizi et al., 2022; Khebizi et al., 2023). For this, I am pleased to invite you to read the part concerning the gypsum implication on the lithological instability in my article published in Larhyss Journal and my oral communications, which expose, for the first time in Algeria, a new concept of the lithological vulnerability of the subsurface. Although the study areas differ, the analysis presented in my work shows the indication of gypsum dissolution at the regional scale as an excellent major risk indicator. The lithological vulnerability of the subsurface concept can be applied to different situations around the world, notably the case of earthquakes. It highlights the hydrodynamic anomalies' relation with the structural and geological context of the area to be studied.
Second, if there is a remarkable increase in calcium concentration in water after the earthquake, how do you explain the reaction of carbonate dissolution and the origin of CO2? Is it linked to magmatic activity? In this case, is there a signature of other gases on other cations? Or is it only related to carbonate since the calcite dissolution is linked to the mineral’s surface to be in direct contact with water?
Allow me to add that the underground water circulation, which is controlled by faults and hydraulic parameters (permeability), determines water-rock equilibrium. In this case, water-rock equilibrium depends on the host rock spatial disposition of rock that guides water mineralization and the different processes. Consequentially, the water-rock equilibrium changes from one area to another due to changes in water mineralization according to the host rock lithology. For this, the information that can be taken from the geological map is that springer’s water is related to ophiolite rocks. So, I think water geochemistry indicates similar water-rock interactions for all sources. However, a mineral’s enrichment zoning can occur due to (i) the meteorological conditions, (ii) the proximity of the springer water from seawater, and/or (iii) the distance from the upstream. The earthquake reconstructed these geothermal fluids depending on the energy released which controls hydrothermal circulation and amplifies interactions with the surrounding environment whether at depth or on the surface. For this, vulnerability zoning in a horizontal and vertical direction can be done according to chemical variation, notably gypsum and probably halite enrichment. It can be indicated as shown in Fig. 8.
Finally, the discussion on this topic is very significant, and the structural and lithological vulnerability and their tracers after the earthquake using vulnerability mapping of the Turkey earthquake seems very interesting for future work.
References:
- Khebizi H., Benlaoukli B., Chaouche M., Chacha B. (2023) The Ghout of El Oued in Algeria: a patrimony and a natural hydro-agrarian alarm system to advance. Larhyss Journal, ISSN 1112-3680, n°55, pp. 107-124.
- Khebizi H., Benlaoukli B., Idri M.L., Mokrani Y., Belabad N. (2023) The vulnerability of the subsoil: a new concept for interpreting the rise in the statistic level of the water table case study of El Oued, Algeria. The First International Conference on Climate Change and Environmental Management: Mitigation Challenges for Sustainable Development. Biskra.
- Khebizi H., Benlaoukli B., Idri M.L., Mokrani Y. (2023) Implication de la dissolution des évaporites sénoniennes sur la stabilité de la subsurface. Cas d’El Oued. Séminaire International Vulnérabilité, Prévention, Adaptation et Résilience des territoires.
Links :
THE GHOUT OF EL OUED IN ALGERIA: A PATRIMONY AND A NATURAL HYDROAGRARIAN ALARM SYSTEM TO ADVANCE | KHEBIZI | LARHYSS Journal P-ISSN 1112-3680 / E-ISSN 2521-9782
(PDF) The vulnerability of the subsoil: A new concept for interpreting the rise in the static level of the watertable Case study of El Oued, Algeria
(PDF) SNECCEA Souk-Ahras 2023 Interprétation de la remontée d'eau par la méthode de corrélation lithostratigraphique Cas d'El Oued
(PDF) La vulnérabilité du Sous-sol : Les évaporites sénoniennes -Cas d’El Oued
Kind regards,
Hafidha Khebizi
Multidisciplinary geologist researcher
https://orcid.org/0000-0002-3020-199
Citation: https://doi.org/10.5194/hess-2024-395-CC3
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