Isotope Composition of Geothermal Fluids Along the North Anatolian Fault Zone: Spatial and Temporal Variations in Relation to Seismic Activities

Proceedings World Geothermal Congress 2005 Antalya, Turkey, 24-29 April 2005

Isotope Composition of Geothermal Fluids along the North Anatolian Fault Zone: Spatial and Temporal Variations in Relation to Seismic Activities

Nilgün Güleç1, David Raymond Hilton2, G.A.M. de Leeuw2, Halim Mutlu3, Selin Süer1, Candan Çifter4 1Middle East Technical University, Department of Geological Engineering, TR-06531, Ankara, Turkey [email protected], [email protected] 2Fluids & Volatiles Lab., Geosciences Research Division, Scripps Inst. of Oceanography, UCSD, La Jolla, CA 92093-0244, USA [email protected], [email protected] 3Osmangazi University, Department of Geological Engineering, TR-26480, Eskişehir, Turkey [email protected] 4General Directorate of Turkish State Hydraulic Works, Dept. of Technical Res. and Quality Control, TR-06100, Ankara, Turkey [email protected]

Keywords: Geothermal Fluids, Isotopic Composition, 3.7.2002 and 13.7.2002 (epicentre: Armutlu-Yalova, M: Monitoring, Seismicity, North Anatolian Fault Zone 3.1). Similarly, although δ13C values in Yalova are < 0 ‰ in almost all sampling periods, an anomalous value (+ 5.79 ABSTRACT ‰) is recorded in March 2002, on the same day (23.3.2002) This study presents results of an on-going monitoring as an earthquake (M: 4.7) occurred in the Sea of Marmara. δ13 programme aimed at characterizing compositional Yet another point to note is the 0.5 – 2 ‰ drop in C variations in geothermal fluids along the North Anatolian values at most sampling sites in October 2002 which is one Fault Zone (NAFZ). The study was initiated through a of the most seismically active months of the monitoring preliminary He-isotope survey in 2000 in response to 2 programme. These compositional variations in geothermal catastrophic earthquakes in 1999 (see results in Chem. fluids probably reflect the effects of seismicity-induced Geol. 2002). The present programme was started in late changes in i) mixing ratios of hot waters with cold, shallow 2001 and covers 9 geothermal sites which are monitored 3 groundwaters, and ii) the balance between mantle-derived times per year. The sites are located along an 800 km long and crustal volatiles. Continuing monitoring of fluid segment of the NAFZ, from Yalova near the Sea of compositions should lead to a better understanding of their Marmara in the west, to Resadiye in the east. The data relationship to seismic activities. reported here cover the results obtained to date from the analyses of i) tritium contents and 18O/16O and D/H ratios of 1. INTRODUCTION the hot and cold waters, along with their major anion-cation Monitoring of the chemistry of geothermal fluids in 13 contents, and ii) CO2/He gas ratios and δ C values of the seismically-active areas is a technique increasingly used for CO2 gas in geothermal fluids. understanding both the mechanisms inducing earthquakes and the associated response in the affected region of the The geothermal waters associated with NAFZ are crust (Thomas, 1988; Toutain and Baubron, 1999). Changes dominantly Na-HCO3, whereas the cold waters are Ca- in the chemical and isotopic composition of the fluids are δ18 δ HCO3 type. The O and D values (-8.29 ‰ to -13.44 ‰ considered to reflect physical and chemical processes and -54.67 ‰ to -96.47 ‰, respectively) reveal meteoric occurring at depth, such as fluid mixing, micro-fracturing origin for both hot and cold waters. Tritium contents range and permeability modification. In this respect, the most between 0-12.55 TU for the hot and 3.00-15.70 TU for the widely-used geochemical parameters are gases like radon, 18 cold waters. The slightly higher δ O values and tritium helium, carbon dioxide, hydrogen, nitrogen and methane, contents of cold waters suggest recharge of cold water and some of the constituents of thermal waters like aquifers from higher altitudes with more recent chlorine, tritium, sulphate and trace metals. A number of precipitation. workers have reported success in their approaches with significant variations in gas and water chemistry observed CO2 concentrations in geothermal fluids range between either prior to or associated with earthquakes. Monitored 3 4 0.02 – 3.02 cm STP/g H2O, and the CO2/ He ratios fall observations include an increase in Rn (Wakita et al., 1980; 3 8 δ 13 between 3.85 x 10 - 3.72 x 10 . C values cover the Teng and Sun, 1986) and H2 (Sato et al., 1986) emissions, range - 4.51 ‰ to + 5.79 ‰, although most of the values large variations in 3He/4He and 13C/12C isotope ratios (Sano are < 0 ‰. Low CO2 concentrations tend to be associated et al., 1986, 1998; Sorey et al., 1996; Hilton, 1996) as well 4 13 with low CO2/ He and high δ C values. as in gas ratios such as He/Ar, N2/Ar, CH4/Ar and CO2/He (Sugisaki and Sugiura, 1986; Hilton, 1996), significant Although no major earthquakes (M>5) occurred along changes in tritium concentrations (Sano et al., 1998), NAFZ over the monitoring period, the temporal variations anomalous increase in Pb concentrations with associated observed in chemical and isotopic compositions appear to changes towards more anthropogenic Pb-isotope correlate with seismicity occurring close to sampling sites. compositions (Poitrasson et al., 1999), and the anomalies Important to note is in this respect the prominent Cl detected in some of the major anion contents (Toutain et al., decrease and concomitant tritium increase (by a factor of 1997; Nishizawa et al., 1998; Balderer et al., 2002). about 1.5 for both) in Yalova hot waters in July 2002, which correlate well with the earthquakes recorded on 1 Güleç et al.

The present study is concerned with monitoring chemical fault zone consists of shorter subparallel fault strands and isotopic compositions of geothermal fluids located locally displaying an anastomosing fault pattern. The NAFZ along the North Anatolian Fault Zone (Figure1), in an extends from eastern Anatolia in the east to the Aegean Sea attempt to determine the possible relation of compositional in the west. Just east of the Sea of Marmara, the fault zone variations to seismic activities. We report here the results bifurcates into two major strands towards the west. The obtained so far from an on-going research project started in northern strand traverses and the southern strand bounds the southern margin of the Sea of Marmara (Figure1). The age late 2001 following a preliminary He-isotope survey (Güleç of dextral motion and the total off-set along the fault zone et al., 2002) in 2000 in response to 2 catastrophic are controversial, covering the range of Middle Miocene- earthquakes in 1999. Included in the project are a total of 9 Early Pliocene and 20-85 km, respectively (see Bozkurt, geothermal sites which are monitored 3 times per year. The 2001 for a review). geothermal sites are located along an 800 km long transect extending from Yalova (near the Sea of Marmara) in the The NAFZ has a remarkable recent seismic activity, the west, through Efteni, Mudurnu, Seben, Bolu, Kurşunlu, most destructive effects of which was experienced by the Hamamözü and Gözlek, to Resadiye in the east (Figure1). 1999 İzmit (M: 7.4; 17 August 1999) and Düzce (M: 7.2; 12 November 1999) earthquakes, resulting in more than 2. TECTONIC SETTING AND RECENT 25,000 fatalities in the region. The August and November SEISMICITY earthquakes occurred, respectively, at depths of 11 km (with two successive shocks in 45 seconds at the centers of North Anatolian Fault Zone (NAFZ) comprises one of the Gölcük and Arifiye) and 10 km (epicenter: Düzce) creating major structures in Turkey that developed during the a total surface rupture length of 177 km from Gölcük neotectonic period in response to the intracontinental eastwards (Koçyiğit et al., 1999a, b; Çemen et al., 2000). convergence following the Late Miocene collision of the The most recent earthquakes along the NAFZ with Arabian promontory with Eurasia (McKenzie, 1972; Dewey magnitudes greater than 3 include: Orta-Çankırı (M: 5.9; 6 and Şengör, 1979; Şengör et al., 1985; Barka, 1992). The June 2000), the Sea of Marmara (M: 4.7; 23 March 2002), NAFZ is a 1500 km long, few hundred meters to 40 km Armutlu-Yalova (M: 3.1; 3 July 2002 and M: 3.1; 13 July wide, dextral strike-slip fault system analogous to the San 2002), Yığılca-Düzce (M: 3.1; 11 October 2002 and M: 4.0; Andreas Fault System in California, and represents an 25 July 2003), Sungurlu-Çorum (M: 3.3; 20 October 2002), intracontinental transform boundary between the Eurasian Mudurnu-Bolu (M: 3.4; 1 November 2002), Çınarcık- plate in the north and the Anatolian plate in the south Yalova (M: 3.5; 22 July 2003) and Bolu (M: 3.5; 7 August (Koçyiğit et al., 1999 a, b). Along much of its length, the 2003 and M: 4.6; 14 April 2004).

BLACK SEA Istanbu l

Bolu ANKARA Karliova

WA GS

NAFZ : North Anatolian Fault Zone EAFZ : East Anat olian Fault Zone N EFZ : Ecemis Fault Zone DSF : Dead Sea Fault MEDITERRANEAN SEA BSZ : Bitlis Suture Zone 0100 WAGS : Western Anatolian Graben System km Gr a b en Strike-Slip Fault Thrust

M = 7.4 BLACK SEA 17.08.99 M = 7.2 12.11.99 N

Kursunlu Gölyaka Arifiye Bolu Ya lova Düzce Gölc ük Hamamözü Gözlek Mudur nu Seben Resadiye

0 50 100 km NAFZ geothermal sites Na Fracture zone associated with Mg Aug.17 & Nov.12 earthquakes Ca Epicenters of the catastrophic 1999 earthquakes HCO3 M = 5.9 Magnitude and date of the catastrophic 1999 SO4 06.06.00 earthquakes Cl

Figure 1: Distribution of the monitored geothermal sites along the NAFZ. Pie diagrams represent the hydrogeochemical facies of the hot waters.

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3. REGIONAL GEOLOGY AND HYDROGEOLOGIC reservoir rocks of the geothermal fields are dominantly OUTLINE Mesozoic limestones, although the Tertiary volcanics comprise the primary reservoir in the Yalova and Kurşunlu The basement in all geothermal fields along the NAFZ is fields (Koçak, 1974; Erişen et al., 1996). Impervious clayey comprised of Paleozoic metamorphics (schists and marbles) levels of the flysch facies and the Neogene sequence act as which are unconformably overlain by Upper Jurassic- cap rocks of the geothermal systems. Lower Cretaceous limestones and Upper Cretaceous flysch consisting of intercalations of limestone, conglomerate, marl, sandstone, claystone and siltstone. Products of a 4. SAMPLING AND ANALYSES widespread volcanic activity, extending from Late In late 2001 (time of commencement of sampling), Cretaceous to Miocene and consisting of basaltic-andesitic sampling could be performed only at the Bolu and Efteni lava flows, tuffs and agglomerates, are observed either as fields due to tough weather conditions. In 2002 and 2003, intercalated with, or as overlying the Upper Cretaceous periodic sampling was performed at 9 geothermal sites flysch. The stratigraphic succession continues with (Yalova, Efteni, Mudurnu, Seben, Bolu, Kurşunlu, Neogene clastics and lacustrine limestones (Şahinci, 1970; Hamamözü, Gözlek and Resadiye) in March-April, July Canik, 1972; Koçak, 1974; Özcan and Ünay, 1978; and October-November periods, with the exception of Müftüoğlu and Akıncı, 1989; Erzenoğlu, 1991; Erişen et al., Reşadiye where the hot-spring source had dried-up in 1996). Plio-Quaternary fluviatile deposits form the October 2002. Both natural springs and production wells youngest units of the succession and are accompanied, in were utilized for sampling (Table 1). the eastern-central segment of the NAFZ, by Plio- 18 16 Quaternary volcanics of limited areal extent (Tatar et al., For major anion-cation chemistry, tritium, O/ O and D/H 1996). isotopic analyses, water samples were collected via filtering into polyethylene bottles. For a better understanding of the Numerous hot-springs emerge in the geothermal fields compositional variations and evaluation of the possible along the fault and fracture zones which probably subsurface processes like mixing and boiling, cold water originated in association with the motion along the NAFZ. samples were collected along with the hot waters, The temperature of the hot-springs range between 30 and commencing in March-April 2002 for the Mudurnu, Seben, 74 °C, and the flow rates range between 0.1 and 5.6 l/s. The Reşadiye and Kurşunlu fields, and in March-April 2003 for the other sampling locations. Table 1: Information relevant to sampling localities, sampling dates and sample types (samples were collected in March- April, July and October-November periods in 2002 and 2003. In late 2001, because of tough weather conditions, sampling could only be performed for gas samples and only at the Efteni and Bolu fields. Red rows in the table represent hot waters, and blue rows represent cold waters)

Locality Samp. *Sample Type Sampling Dates No. Efteni-Gölyaka 1a Spring 16/11/2001 23/3/2002 8/7/2002 27/10/2002 7/4/2003 9/7/2003 15/10/2003 Efteni-Gölyaka 1b Spring - - - - 7/4/2003 9/7/2003 15/10/2003 Yalova-Termal 2a Spring - 24/3/2002 9/7/2002 28/10/2002 8/4/2003 10/7/2003 16/10/2003 Yalova-Termal 2b Spring - 24/3/2002 9/7/2002 28/10/2002 8/4/2003 10/7/2003 16/10/2003 Yalova-Termal 2c Spring - - - - 8/4/2003 10/7/2003 15/10/2003 Bolu- Karacasu Termal 3a Production well (P) 18/11/2001 24/3/2002 9/7/2002 28/10/2002 9/4/2003 10/7/2003 16/10/2003 Bolu- Karacasu Termal 3b Spring - - - - 9/4/2003 10/7/2003 16/10/2003 Babas-Mudurnu 4a Production well (A) - 25/3/2002 10/7/2002 29/10/2002 9/4/2003 11/7/2003 17/10/2003 Babas-Mudurnu 4b Production well (A) - 25/3/2002 10/7/2002 29/10/2002 9/4/2003 11/7/2003 17/10/2003 Babas-Mudurnu 4c Spring - 25/3/2002 10/7/2002 29/10/2002 9/4/2003 11/7/2003 17/10/2003 Babas-Mudurnu 4d Spring - 25/3/2002 10/7/2002 29/10/2002 9/4/2003 11/7/2003 17/10/2003 Seben-Pavlu 5a Spring - 25/3/2002 10/7/2002 29/10/2002 9/4/2003 11/7/2003 17/10/2003 Seben-Pavlu 5b Production well (P) - 25/3/2002 10/7/2002 29/10/2002 9/4/2003 11/7/2003 17/10/2003 ‡Seben-Pavlu 5c Production well (P) - 25/3/2002 - 29/10/2002 - 11/7/2003 - ‡Seben-Pavlu 5d Spring - 25/3/2002 - 29/10/2002 9/4/2003 11/7/2003 17/10/2003 Hamamözü-Arkutbey 6a Production well (A) - 26/3/2002 11/7/2002 30/10/2002 10/4/2003 12/7/2003 18/10/2003 Hamamözü-Arkutbey 6b Spring - - - 30/10/2002 10/4/2003 12/7/2003 18/10/2003 Gözlek-Amasya 7a Production well (A) - 27/3/2002 12/7/2002 31/10/2002 10/4/2003 12/7/2003 18/10/2003 Gözlek-Amasya 7b Spring - - - 31/10/2002 10/4/2003 12/7/2003 18/10/2003 ‡‡Reşadiye-Tokat 8a Spring - 27/3/2002 12/7/2002 - - - - Reşadiye-Tokat 8b Spring - 27/3/2002 12/7/2002 31/10/2002 - - - Kurşunlu-Çavundur 9a Production well (A) - 28/3/2002 13/7/2002 1/11/2002 11/4/2003 12/7/2003 19/10/2003 §Kurşunlu-Çavundur 9b Spring - 28/3/2002 13/7/2002 1/11/2002 11/4/2003 - - Kurşunlu-Çavundur 9c Spring - 28/3/2002 13/7/2002 1/11/2002 11/4/2003 12/7/2003 19/10/2003

*A: Artesian, P: Pumping ‡since mud removal studies (following the heavy rain) were being performed in Seben, no sampling could be done in July 2002 period from localities 5c and 5d; likewise, since the pump was removed from the well, no sampling could be performed in Seben in March-April 2003 and October 2003 periods from locality 5c. ‡‡ since the spring had dried up, no sampling could be performed from Reşadiye in periods following July 2002. § since the spring had dried up, no sampling could be performed from locality 9b in periods following April 2003.

3 Güleç et al.

For the measurement of gas ratios (CO2/He) and the sediments, including impermeable clayey levels, is isotopic composition (δ13C) of the gases, geothermal fluids probably responsible for the dominance of Na cation in the were collected in annealed copper tubes, which were sealed hot waters. The Na-SO4 character of waters in Yalova in the field using a cold welding tool. probably has genetic connections with the young organic accumulations in the Izmit Bay (located to the north of Anion-cation chemistry, tritium, 18O/16O and D/H analyses Yalova). of water samples were carried out at the laboratories of the Turkish State Hydraulic Works. Anion-cation analyses Although hydrogeochemical facies defined by dominant were performed by conventional methods (titration for Ca, anion-cation pairs stay fairly constant, temporal variations Mg, HCO3, CO3 and Cl, flame photometry for Na and K, were recorded in the chemical composition of waters during and spectrophotometry for SO4). Tritium contents were the course of the monitoring period from March-April 2002 determined by Liquid Scintillation Counting System to October-November 2003. Of these, variations in Cl (Packard Tri-Carb 2260 XL) after electrolytic enrichment. contents (Figure 2) appear to be particularly significant as δ18O and δD ratios were measured on a Micromass 602 C Cl is considered to be a conservative constituent used as Mass Spectrometer. tracer. In this respect, a 1.5 fold decrease in the Cl content of Yalova hot water in 9 July 2002 (compared to March 13 12 CO2/He gas ratios and C/ C ratios of the CO2 gas in 2002 and October 2002 periods) deserves attention as it geothermal fluids were measured on VG Prism and points to a hot water-cold water mixing that might have quadrupole mass spectrometers at the Geosciences been induced by the seismic activities occurring on the 3rd Research Division, Scripps Institution of Oceanography. and/or 13th of July 2002 in Armutlu-Yalova (M: 3.1). Additionally, the continuous decrease in the Cl content of 5. CHEMICAL COMPOSITIONS Kuşunlu sample 9b (from 210 mg/l in March 2002 to 82 mg/l in April 2003) is also worth to note. This decrease can The hot waters are almost all Na-HCO3 type waters (Efteni, be attributed to either i) an anomaly in March 2002, with Seben, Gözlek, Reşadiye and Kurşunlu samples), except for the return of Cl contents to their original values in time, or the Ca-HCO3 type (Bolu and Mudurnu), and Na-SO4 type ii) a hot -cold water mixing process triggered by seismic (Yalova) (Figure1). Additionally, Hamamözü hot water activities following March 2002, with an increase in the displays a mixed character with none of the ions exceeding cold water component in time. Since the seismic records 50 % of the total composition. The cold waters, on the other following April 2002 indicate an increase both in the hand, are dominantly Ca-HCO3 type. The bicarbonate frequency and the magnitude of earthquakes in the Çankırı character of waters seems to be compatible with the region, the second alternative seems to be more likely. dissolution of the reservoir rocks that are dominated by Mesozoic limestones; ion exchange with the overlying

Hot Waters

250 Hot W aters Seismicity with increasing 200 March 02 frequency since Apr. 2002 840 Marc h 02 3.7.2002 & 13.7.2002 M: 2.1-4.0 July 02 July 02 150 800 Armutlu-Yalova M: 3.1 October 02 October 02 Cl Cl April 03 760 April 03 100 July 03 July 03 720 October 03 50 October 03 8a 9a

0 1a 2a 2b 3a 4a 4b 5a 5b 5c 6a 7a 9b

Cold Waters

250

200 March 02 July 02 150 October 02 Cl 100 April 03 July 03 50 October 03

0 1b 2c 3b 4c 4d 5d 6b 7b 8b 9c

Figure 2: Concentration vs. Sample No. depicting temporal variations in Cl contents of hot and cold waters.

4 Güleç et al.

6. OXYGEN- AND HYDROGEN- ISOTOPE increase in the Mudurnu cold water sample is likely to COMPOSITIONS reflect seasonal effects (precipitation and evaporation), while in Bolu the variations in hot water may be attributed to the 18 The δ O values of the hot waters recorded over the effects of a possible hot-cold water mixing process. monitoring period range between -13.44 ‰ and -8.37 ‰, Although there appear to be two seismic events in Bolu on while the cold waters have values ranging from -12.71‰ to - 21 October 2002 and 1 November 2002 (M: 2.6 and 2.4, 8.29‰. The δD values have ranges between -96.47 ‰ and - respectively) that can be related to this mixing process, the 64.15 ‰ for the hot waters, and between -86.7 ‰ and -54.67 effects of these events are not observed in the other ‰ for the cold waters. The isotope compositions of the parameters (e.g. Cl and/or tritium contents). waters are presented as δ18O vs. δD diagram in Figure 3, where the data plotted represent the mean values of the 7. TRITIUM CONTENTS measurements throughout the monitoring period (from Tritium (3H) contents for the hot waters range between 0- March-April 2002 to October-November 2003). As can be 12.55 TU, with the majority being less than 5 TU. For the seen from Figure 3, some of the samples lie along and/or cold waters, the range is 3.00-15.70 TU, although most of close to the Global Meteoric Water Line (GMWL) (defined the samples have concentrations above 8 TU. The relatively by Craig et al., 1961) whereas others plot away from it. The high tritium contents of cold waters suggest recharge of cold samples plotting away from the GMWL include not only the water aquifers with more recent precipitation. hot but also the cold waters whose aquifers are supposed to be recharged by meteoric precipitation. This suggests that The temporal variations of tritium contents are shown in local meteoric water lines are different from the GMWL). It Figure 6. The interpretation of these variations requires is worth to note here that whether the cold waters define particular caution since the analytical errors associated with their own trends or whether they plot along the GMWL, tritium contents are high in some sampling periods their hot water companions also plot along the same trends (approaching ± 2 TU) depending on the high background (e.g. see Mudurnu, Yalova and Seben samples in Figure 3) level in the counter. Nevertheless, the high tritium content of suggesting a meteoric origin for both the hot and cold the Yalova hot waters in July 2002 period deserves attention waters. Only in the Kurşunlu field, the hot water sample (no. as it is accompanied by a decrease in Cl content (see section δ18 9a) has a relatively high O value, reflecting 5 and Figure2). Since deep circulating hot waters are characterized by high Cl - low tritium, and cold shallow An interesting point to note as to the isotope compositions of waters by low Cl – high tritium contents, this positive the samples is that in almost all geothermal fields (except δ δ18 tritium anomaly (and the associated negative Cl anomaly) in Kurşunlu and Bolu), the hot waters have D and O July 2002 may imply a hot water-cold water mixing process values lower than their cold water companions suggesting possibly triggered by the 3rd and/or 13th July 2002 recharge of the hot water aquifers from higher altitudes earthquake(s) in Armutlu-Yalova (M: 3.1). (compared to the altitudes where cold water aquifers are recharged). In the Kurşunlu field, the tritium content of sample no. 9b displays an increasing trend with time. Although the δ18 δ The temporal variations in O and D values, exceeding significance of this trend can be questioned, it is correlated the limits of analytical errors (0.1 ‰ and 1 ‰, respectively), with the decreasing Cl trend mentioned above (section 5) appear to be more prominent in the Bolu and Hamamözü and appears to support the idea of mixing whereby the cold fields (Figure 4 and 5). These variations are observed i) in water component increased in time in relation to the October 2002 in the hot water sample from Bolu, and ii) in increasing frequency and magnitude of seismic activities in April 2003 in the cold water sample from Mudurnu. The Çankırı since April 2002.

-50,0 Efteni-hot Efteni-cold GMWL Yalova-hot Yalova-cold Bolu-hot Bolu-cold -75,0 Mudurnu-hot Mudurnu-cold Seben-hot Seben-cold

D ‰ 9a Hamamözü-hot δ Hamamözü-cold -100,0 Gözlek-hot Gözlek-cold Reşadiye-hot Reşadiye-cold Kurşunlu-hot Kurşunlu-cold -125,0 GMWL -14,0 -11,5 -9,0 -6,5 δ18 O‰

Figure 3: δ18O vs. δD diagram. Data plotted represent the mean values of the measurements throughout the monitoring period from March-April 2002 to October-November 2003; GMWL: Global Meteoric Water Line from Craig et al. (1961).

5 Güleç et al.

02 r r 03 02 r 02 r 03 02 e 3 2 e 03 3 e 02 b l 0 03 be ch 0 b il 0 b ly to o r ly to arch u c pri uly ct ar uly cto p u c M J O A J O M J O A J O -10 -8 Efteni-Gölyaka-1a -9 Efteni-Gölyaka-1b -11 Ya l ova - 2a O ‰

O ‰ -10 Ya l ova - 2b 18 18

δ -12 Ya l ova - 2c δ -11

-13 -12

2 3 0 0 02 r r 02 03 03 3 e r r h 02 l 0 02 2 e 03 3 e c tobe ri ly tob 0 l 0 b ar uly c p u c rch ly tob ri to M J O A J O a u c p uly c M J O A J O -8 21.10.2002 Bolu-Center M:2.6 1.11.2002 Mudurnu-Bolu M:3.4 -8 -9 -9 Mudurnu-4a -10 -10 Mudurnu-4b O ‰ -11 O ‰ Mudurnu-4c 18 -11 18

δ Mudurnu-4d -12 δ -12 -13 Bol u-3a -13 Bol u-3b

02 2 3 r r 03 r 0 r 0 02 03 3 e 02 e 3 e ch 02 be l 0 r ly o ly 02 l 0 03 a u ct pr i u ctob arch ctob pr i ctob M J O A J O M July O A July O -8 -8 -9 Seben- 5a -9 -10 Hamamözü-6a Seben- -10 O ‰ -11 O ‰ Hamamözü-6b 5b -11 18 -12 18

δ Seben- δ -12 -13 5c -14 Seben- -13 5d

2 0 02 r 3 r 03 h be c 02 o l 0 03 3 ly ri ly tobe 02 2 e... 0 3 e... ar u ct p u c h 0 l 0 M J O A J O rc ly tob ly tob a u c pr i u c -8 M J O A J O -9 -11 Re şadiye 8a -10 O ‰ -12 Re şadiye 8b 18 -11O ‰ Gözl ek-7a

δ -13 18 -12 Gözl ek-7b -13δ -14

2 3 0 r r 0 02 e 3 e 02 l 03 0 b rch ly o a ctob pr i u ct M July O A J O -8 -9

-10O ‰

18 Kurşunlu-9a -11δ Kurşunlu-9b -12 Kurşunlu-9c

Figure 4: Temporal variations in oxygen-isotope compositions. Red symbols represent the hot, blue symbols represent the cold waters.

6 Güleç et al.

02 r 02 r 03 2 r 02 2 e e 3 er 03 h 0 l 03 b h 0 02 l 03 b rc y tobe y 03 to ri y 0 a ul c pri ul c arc ctob p cto M J O A J O M July O A Jul O -77 -50 Yalova-2a -79 -60 Yalova-2b -81 -70 D ‰ D ‰

δ δ Yalova-2c -83 Efteni-Gölyaka-1a -80 -85 Efteni-Gölyaka-1b -90

2 2 r 0 r 03 0 er 02 r 03 02 e h 02 l 03 03 02 b l 03 03 y tob ri y o arc c p l ctobe arch uly ct pri uly ctobe M Jul O A Ju O M J O A J O -60 21.10.2002 Bolu-Center M: 2.6 -65 Mudurnu-4a -70 1.11.2002 Mudurnu-Bolu M: 2.4 -70 -75 Mudurnu-4b -80 D ‰ D ‰ -80

δ δ Mudurnu-4c -90 Bolu-3a -85 Mudurnu-4d -100 Bolu-3b -90

2 r 02 r 03 2 0 0 r 3 r 03 h 02 l 03 l 03 0 rc y 02 y 03 y 02 tobe i a ul ctobe pri ul ctobe arch c pr ly ctobe M J O A J O M Jul O A Ju O -60 -60 Seben-5a -70 -70 Seben-5b Hamamözü-6a -80 -80 D ‰ D ‰ Hamamözü-6b

δ Seben-5c δ -90 -90 Seben-5d -100 -100

2 3 3 r 0 r 0 2 r 02 0 2 3 0 2 3 r h 02 0 be l 0 l 03 y o y 03 y 0 ri y 0 arc ul ct pri ul ctobe arch ctobe p l ctobe M J O A J O M Jul O A Ju O -60 -80 -70 Reşadiye-8a Gözl ek -7a -85 -80 Reşadiye-8b D ‰ D ‰

δ Gözl ek -7b δ -90 -90 -100 -95

02 2 r 02 er 03 0 l 03 b rch y 03 to a ctobe pri l c M July O A Ju O Kurşunlu-9a -70 Kurşunlu-9b -75 Kurşunlu-9c -80

D ‰ -85 δ -90 -95

Figure 5: Temporal variations in hydrogen-isotope compositions. Red symbols represent the hot, blue symbols represent the cold waters.

7 Güleç et al.

Efteni-Gölyaka-1a 14 03.7.2002 & 13.7.2002 Yalova-2a Armutlu-Yalova Efteni-Gölyaka-1b 12 M: 3. 1 Yalova-2b 6 10 Yalova-2c 4 8 TU TU 2 6 4 0 2 2 0 03 03 02 r 02 y r 03 0 rch uly pril ul a J A J M ctobe ctobe O O 2 3 3 02 02 0 0 03 0 y y r h l r l e rc u pril u b a J A J M ctobe cto O O

16 18 Mudurnu-4a 16 14 Bolu-3a 14 Mudurnu-4b 12 Bolu-3b 12 Mudurnu-4c 10 10 Mudurnu-4d 8 TU TU 8 6 6 4 4 2 2 0 0

2 2 2 3 3 2 2 3 0 0 0 0 0 0 03 03 0 r 0 il r 03 ly r 02 r ly e r u uly e rch Ju p July J pril J a A arch A tob M ctob ctobe M ctobe c O O O O

12 14 10 12 10 8 Seben-5a 8 6 Seben-5b TU TU Seben-5d 6 Hamamözü-6a 4 Seben-5c 4 Hamamözü-6b 2 2 0 0

3 2 03 3 02 02 03 0 02 03 0 02 y r l 0 y r 03 h r 02 ly r l e i l e u e u pr u July pril J b arch J b A J arc A M tob M ctobe cto cto c O O O O

12 10 9 10 8 8 7 Gözl ek-7a 6 6 Reşadiye-8a

TU 5 Gözl ek-7b TU 4 4 Reşadiye-8b 3 2 2 1 0 0

2 2 3 02 0 0 0 03 2 r il r 03 02 03 ch uly e uly 0 r 02 il 03 r 03 r J pr J ch e ly a A r July pr Ju M ctob ctobe a tob A O O M c ctobe O O

Seismicity with increasing 18 frequency since Apr. 2002 M: 2.1-4.0 16 14 12 10 Kurşunlu-9a

TU 8 Kurşunlu-9b 6 Kurşunlu-9c 4 2 0

2 3 02 03 0 02 r 0 il r 03 rch uly be pr uly a J A J M cto ctobe O O

Figure 6: Temporal variations in tritium concentrations Red symbols represent the hot, blue symbols represent the cold waters.

8 Güleç et al.

8. CARBON ISOTOPE COMPOSITIONS Yığılca-Düzce (M:3.1; 11.10.2002) and Sungurlu-Çorum (M: 3.3; 20.10.2002) earthquakes, and the earthquake δ13 The C values of the CO2 gas in the geothermal fluids are swarm in Hendek-Sakarya (M: 2.5-2.9; 27.10.2002). These shown in Figure 7. As can be seen from the figure, except decreases in δ13C values may indicate gas release from the for the Yalova and – to some extent - Kurşunlu fields, the mantle and/or marine carbonates in these geothermal fields δ13 values are mostly below 0‰ and indicate mantle [ C : (- which may have been induced by the above mentioned δ13 3‰)–(-8‰)] and/or marine carbonate [ C : (-1‰)– earthquakes. (+2‰)] contributions to the CO2 gas. Regarding the Yalova δ 13 sample, although C values are below 0 ‰ in almost all 9. CO2 CONCENTRATIONS AND CO2/He GAS sampling periods, an anomalous value (+ 5.79‰) is RATIOS recorded in March 2002. Such a high value can probably be attributed to the thermo-metamorphic decay of carbonates. CO2 concentrations in geothermal fluids range between 3 4 It is worth to note here that the sampling in Yalova was 0.02 – 3.02 cm STP/g H2O, and the CO2/ He ratios fall rd 3 8 performed on the 23 of March 2002, on the same day as between 3.85 x 10 - 3.72 x 10 (Figure 8). Low CO2 4 the seismic activity (M: 4.7) recorded in the Sea of concentrations tend to be associated with low CO2/ He and 13 4 Marmara. This seismic activity may be the triggering high δ C values. In Yalova, however, the high CO2/ He mechanism of the thermo-metamorphic process. ratio in March 2002 period is associated with high δ13C ratio which may be correlated with the seismic activity (M: Another important point to note is the 0.5 – 2 ‰ drop in 4.7) recorded on 23rd March 2003 in the Sea of Marmara. 13 δ C values at the Seben, Mudurnu, Hamamözü and Gözlek The seismic activity, as discussed in section 8, might have fields in October 2002, which is one of the most seismically induced CO2 gas escape from crustal levels (probably in active months of the monitoring programme including the connection with thermo-metamorphic processes). 8 23.3.2002 Sea of Marmara M: 4.7 6 11.10.2002 Yığılca-Düzce M: 3.1 20.10.2002 Sungurlu-Çorum M: 3.3 18-Nov-01 4 27.10.2002 Hendek-Sakarya M: 2.5-2.9 1.11.2002 Mudurnu-Bolu M: 3.4 24.Mar.02 2 9-Jul-02 C

13 29-Oct-02 δ 0 9-Apr-03 10-Jul-03 -2

-4

-6

u ü k e va e y o ol en l l B z di unlu Efteni a eb ö a ş Y S G ş Mudurnu amamöz Re Kur H

13 13 Figure 7: δ C vs. Locality diagram depicting temporal variations in δ C values of CO2 gas. Since the Cu-tubes leaked, no measurements could be performed for sample no. 9a from the Kurşunlu field for the March 2002 period, and for sample no. 2a from Yalova for the July 2002 period.

1,00E+09

1,00E+08 23.3.2002 Sea of Marmara M: 4.7 1,00E+07 He 4 1,00E+06

Nov 01 CO2/ 1,00E+05 Mar-02 July 02 1,00E+04 Oct 02 Apr 03 July 03 1,00E+03

) ) ) ) ) ) ) ) ) 3 (5 (6 8 9 ni(1 ü e va(2 olu( nu(4 en z ft o r b nlu ( E al B e mö özlek(7 adiye( u Y du S G ş ş u e ur M ama R K H

4 4 Figure 8: CO2 / He vs. Locality diagram depicting temporal variations in CO2 / He ratios. Since the Cu-tubes leaked, no measurements could be performed for sample no. 9a from Kurşunlu field for March 2002 period.

9 Güleç et al.

10. CONCLUSIONS Bitirme Raporu, MTA Report, No. 8714, Ankara (1989). 1. The geothermal waters associated with NAFZ are dominantly Na-HCO3, whereas the cold waters are Ca- Güleç, N., Hilton, D. R., and Mutlu, H.: Helium and Heat HCO3 in character. Distribution in Turkey: Relations to Tectonic Provinces, Volcanism and Recent Seismic Activities, 2. The oxygen- and hydrogen-isotope compositions point Chem. Geol., 187, 129-142, 2002. to a meteoric origin for both the hot and the cold waters. The slightly higher δ18O- δD values and tritium Hilton, D. R.: The Helium and Carbon Isotope Systematics contents of cold waters suggest the recharge of cold of a Continental Geothermal System: Results from water aquifers from higher altitudes with more recent Monitoring Studies at Long Valley Caldera precipitation. (California, U.S.A.), Chem. Geol., 127, 269-295, 1996. 3. 13C/12C ratios of geothermal fluids suggest mantle Koçak, A.: Çavundur (Kurşunlu-Çankırı) Kaplıca and/or marine carbonate contributions to the CO2 gas Bölgesinin Hidrojeoloji Etüdü Raporu, MTA Report, in geothermal fluids. High δ13C values tend to be No.6373, Ankara (1974). associated with low CO concentrations and low 2 Koçyiğit, A., Bozkurt, E., Cihan, M., Özacar, A., and CO /4He ratios. 2 Teksöz, B.:. Neotectonic Framework of Turkey: A 4. Temporal variations in chemical and isotopic Special Emphasis on the 17 August 1999 Gölcük- compositions of geothermal fluids appear to correlate Arifiye Earthquake (NE Marmara, Turkey). with the seismic activities recorded during the course Proceedings, International Conference on Earthquake of the monitoring period from late 2001 to late 2003. Hazard and Risk in the Mediterranean Region, Near 13 4 δ C values, CO2/ He gas ratios, Cl and tritium East University, Cyprus (1999 a). contents seem to be the most sensitive parameters, and Koçyiğit, A., Bozkurt, E., Cihan, M., Özacar, A., and Yalova geothermal field deserves particular attention Teksöz, B.: 12 Kasım 1999 Dağdibi (Düzce-Bolu) in this respect. Depremi. Geological Reconnaissance Report, 5. The temporal variations in geothermal fluids’ Department of Geological Engineering, Middle East compositions probably reflect the effects of seismicity- Technical University, Ankara (1999 b). induced changes in hot/cold water ratios in subsurface Mc Kenzie, D.P.: Active Tectonics of the Mediterranean mixing processes, and the balance between mantle- Region. Geophys. J. R. Astron. Soc., 30, 109-185, derived and crustal volatiles. Continuing monitoring of 1972. compositions should lead to a better understanding of the relation to seismic activities. Müftüoğlu, E., and Akıncı, K.: Bolu-Seben Kesenözü Kaplıcası ve Çevresi Jotermal Enerji Aramaları Sismik REFERENCES Etüd Raporu, MTA Report, No. 8856, Ankara (1989).

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