- Email: [email protected]
Radon anomalies along faults in North of Jordan
Radiation Measurements 34 (2001) 397–400
www.elsevier.com/locate/radmeas
Radon anomalies along faults in North of Jordan M.H. Al-Tamimia; ∗ , K.M. Abumuradb a Department
of Earth and Environmental Sciences, Yarmouk University, PO Box 566, Irbid 211-63, Jordan of Physics, Yarmouk University, PO Box 566, Irbid 211-63, Jordan
b Department
Received 28 August 2000; received in revised form 27 November 2000; accepted 30 January 2001
Abstract Radon emanation was sampled in .ve locations in a limestone quarry area using SSNTDs CR-39. Radon levels in the soil air at four di3erent well-known traceable fault planes were measured along a traverse line perpendicular to each of these faults. Radon levels at the fault were higher by a factor of 3–10 than away from the faults. However, some sites have broader shoulders than the others. The method was applied along a .fth inferred fault zone. The results show anomalous radon level in the sampled station near the fault zone, which gave a radon value higher by three times than background. This study draws its importance from the fact that in Jordan many cities and villages have been established over an intensive faulted land. Also, our study has considerable implications for the future radon mapping. Moreover, radon gas is proved to be a good tool for c 2001 Elsevier Science Ltd. All rights reserved. fault zones detection. Keywords: Radon; Soil; Fault zones delineation; Plastic detectors
1. Introduction The use of radon as a geological tracer has been developed mainly in connection with uranium prospecting, environmental research, earthquake and volcanic prediction, thermoluminescence dating of ancient ceramics and fault zones con.rmation (King, 1980; Gingrich, 1984). Radon (222 R), an alpha emitting noble gas is produced in the radioactive decay series of uranium (238 U). It tends to migrate from its source mainly upwards. Its rate of migration and its soil-gas concentration are controlled by a large number of factors, such as the distribution of uranium in the soil and bed rock, soil porosity and humidity, microcracks, granulation, surface winds and so on. Durrani and Ili=c (1997) discussed the relation between geology and radon levels in groundwater, soil gas, and indoor air. Knowledge of the levels of radon in the soil gas and underground water or in the dwelling’s atmosphere is necessary to protect populations from the consequences of excessive exposure to radiation, for example from the risk of lung cancer (Nero, 1990). ∗ Corresponding author. Fax: +962-2-7274725. E-mail address: [email protected] (M.H. Al-Tamimi).
The amount of radon emitted from the earth crust into atmosphere is usually small. However unusual quantities of radon could be emitted above geological faults, geothermal sources, uranium deposits and volcanoes (Nishimura and Katsura, 1990). These anomalies of radon are subject to the emanation power of soils and rocks, to the mechanisms of migration and to the climate factors (Magro-Campero and Fleischer, 1977). In Jordan, radon emanations were measured in soils, rocks and indoor atmosphere in di3erent cities (Abumurad et al., 1997). Radium, the immediate precursor of radon gas, occurs virtually in all types of rocks and soils; its concentration varies from site to site and with the change of geological criteria. The present radon survey conducted in a quarry area located southwest of Irbid city in north Jordan, characterized by a homogenous lithology is expected to show similar radon emanation levels. However, the existence of fault zones in such locations would cause an increase in radon concentration along these faults. These fault zones are easily located and their attitudes can be measured through the quarry face. The color of the .lling materials along faulted zones becomes rosy to pale red due to the formation of di3erent iron oxides as a result of weathering
c 2001 Elsevier Science Ltd. All rights reserved. 1350-4487/01/$ - see front matter PII: S 1 3 5 0 - 4 4 8 7 ( 0 1 ) 0 0 1 9 3 - 7
398
M.H. Al-Tamimi, K.M. Abumurad / Radiation Measurements 34 (2001) 397–400
process of the crushed materials along these zones. The goals of the present work were to assure the suitability of this method to con.rm the existence of fault zones, to help in radon mapping and for epidemiological studies in Jordan.
four di3erent quarries. A .fth location was chosen where geomorphological criteria and geological map indicate an inferred fault. 3. Methodology
2. Geological setting The study area has a uniform thin soil cover. The underlying bedrock is characterized by uniform geophysical and geochemical properties such as porosity, mineral composition and almost homogenous thickness distribution (Bender, 1968, 1974). Moreover the bedrock in this area possesses a uniform lithology (Fig. 1) and belongs to one rock unit, which is called Wadi um Ghudran (WG) Formation (Massri, 1963). This rock unit consists of few meters of intercalations of soft white chalk and chalky limestone, which overlies a thick sequence of massive white hard limestone, that was called by Massri (1963) as Wadi Es-sir Formation. Fortunately, large number of limestone quarries in the area enabled us to easily locate fault zones and de.ne their attitudes in quarry face. However, the area under investigation is full of traceable and inferred faults. Four easily traceable, almost vertical faults were chosen from
Square pieces (1:5 cm × 1:5 cm) of solid-state nuclear track detectors (SSNTDs) CR-39 were mounted on the bottom of cylindrical plastic cans (Abumurad et al., 1994). The lid of each can is punched with few holes; these holes are then covered with thin (0:5 cm) pieces of sponge to .lter out 220 Rn. The resulted detectors were previously calibrated. Five holes of 50 cm depth were dug in each selected site and arranged in a line perpendicular to the fault trace: one hole, the third, lies on the fault zone, while two holes were located on the right- and on the left-hand side of the fault trace. The distance between adjacent holes was about 10 m. Furthermore, two detectors were put together upside down in each hole and then buried again. Planting of detectors was done with care so as not to disturb the soil cover in all sites. This work was carried out during August 1999. After 2 weeks the detectors were collected and chemically etched ◦ using 6N KOH at 70 C for 8:5 h. The density of alpha
Fig. 1. Map of the study area of Irbid city showing its geological criteria and locations of all sampled sites.
M.H. Al-Tamimi, K.M. Abumurad / Radiation Measurements 34 (2001) 397–400
tracks in the plastic detectors was counted using an optical microscope.
4. Results and discussions We assume that radon concentration should be similar in all measured holes as long as the depth of the detectors is constant, the type of soil is homogenous and the type of bed rock is the same all over the study area. Therefore, unusual increase in measured radon concentration should be related mainly to the existence of the fault zones. The rock along these zones are highly deformed and crushed to a great depth, which allows pathways for radon to migrate and di3use. The collected data from all sites and holes (samples) are displayed in Fig. 2. The radon concentration measured at two ends (i.e. No. 1, which is −20 m away from a fault and No. 5, which is 20 m on the other side of the fault) of each traverse is considered as background. The highest radon concentration value was recorded in the central sample (i.e. hole No. 3, which is 0 m from the fault), which is located almost over the fault zone. For example radon level increases as one goes along the traverse line from sample No. 1 to No. 2 to reach the maximum over sample No. 3 and then decreases again towards the other end of the traverse. The maximum value of radon level for a given site ranges from three to 10 times the minimum value of that site. In the .fth site of the inferred fault, radon concentrations have similar trend as in other sites. These radon concentration anomalies can be related to the expected changes of the properties of the rocks along
399
these fault zones. The rocks are crushed during faulting process. Therefore, faulting is usually accompanied with certain changes in its geological characteristics, such as a large increase in the porosity and permeability of the deformed rocks along these zones. Through this porous and permeable medium radon migrates upwards more easily (King, 1980; Kresl et al., 1993a, b). Besides, the crushed rocks along fault zones are also characterized by grain size reduction, which will a3ect also uranium-bearing minerals found in the rock body. This process will cause an increase in radon emanation (Gundersen and Linda, 1991). Furthermore oxidation of iron during faulting deformation and subsequent weathering, results in distinctive iron-staining nature of many fault zones. Iron oxides and other metal oxides scavenge uranium and radium available through the weathering processes. These processes increase the radon emanation from rocks and soils, and make radon readily available to local groundwater (Choubey and Ramola, 1997). Moreover, shoulders (i.e., radon levels in the samples just o3 the fault zone) of site 4 are broad, while that of site 5 are thin. This variation in shoulders among sites may be due to the thickness variations of fault zones. 5. Conclusion Radon sampling across faults has added to our understanding of how they vary spatially. This study is the .rst in Jordan to use “radon tool” to study the existence of fault zones in such locality. Highly localized variations in the radon levels on scale of several meters have been observed. Radon anomalies, of up to several thousands Bq=m3 , are not supported by local uranium. Radon levels over the fault zones are up to 10 times the background values. Using this tool with shorter distance between measuring samples (holes) one can estimate the width of the deformed fault zone just beneath thin soil layer covering this structure. This study draws its importance from the fact that in Jordan many cities and villages have been established over the western part of Jordan, which is an intensively faulted area located adjacent to the active transform Araba-Jordan rift. Moreover, applying this method will provide more information about faulted areas in Jordan and its radon distribution. It has been reported (Varley and Flowers, 1998) that levels as low as 10 kBq=m3 in the soil gas could produce an indoor radon concentration above the UK action level of 200 Bq=m3 . However, it is known that each 1 Bq=m3 of radon level means about 0:015 mSv=y (ICRP, 1993). So our results have considerable implications for the future of radon mapping and for epidemiological studies in Jordan.
References Fig. 2. Measured radon concentration values in soil gas.
Abumurad, K.M., Al-Bataina, B., Ismail, A., Kullab, M.K., Al-Eloosy, A., 1997. Survey of radon levels in Jordanian
400
M.H. Al-Tamimi, K.M. Abumurad / Radiation Measurements 34 (2001) 397–400
dwellings during an autumn season. Radiat. Prot. Dos. 69 (3), 221–226. Abumurad, K.M., Kullab, M.K., Al-Bataina, B.A., Ismail, A.M., Lehlooh, A.D., 1994. Estimation of radon concentrations inside houses in some Jordanian regions. Mu’tah J. Res. Stud. 9, 9–21. Bender, F., 1968. Geological map of Jordan. Bundesanst. Bodenforschung, Hannover. Bender, F., 1974. Geology of Jordan. Borntraeger, Stuttgart, p. 196. Choubey, V., Ramola, R., 1997. Correlation between geology and radon levels in groundwater, soil and indoor air in Bhilangana Valley, Garhwal Himalaya India. Environ. Geol. 32 (4), 258–268. Durrani, S.A., Ili=c, R. (Eds.), 1997. Radon Measurements by Etched Track Detectors: Application to Radiation Protection, Earth Sciences and the Environment. World Scienti.c, Singapore. Gingrich, J.E., 1984. Radon as geochemical exploration tool. J. Geophys. Explor. 21, 19–39. Gundersen, L.C.S., Linda, C.S., 1991. Radon in sheared igneous and metamorphic rocks. In: Gundersen, L.C.S., Wanty, R.B. (Eds.), Field Studies of Radon in Rocks, Soil and Water, US Geol. Survey Bull. 1991, 39 –50. ICRP, 1993. Protection against radon at home and at work. Ann. ICRP 65 (4), 5.
King, C., 1980. Episodic radon changes in subsurface soil gas along active fault and possible relation to earthquakes. J. Geophys. Res. 85 (B6), 3065–3078. Kresl, M., Vakova, V., Klecka, M., 1993a. Radon in soils overlaying several tectonic zones of the south Bohemian Moldanubicum. Jb. Geol. B. A. 136, Hf4, 799–808. Kresl, M., Vakova, V., Klecka, M., 1993b. Distribution of radon anomalies over the Choustnik fault zone (Central Bohemia). J. Czech Geol. Soc. 38, 225–233. Magro-Campero, A., Fleischer, R.L., 1977. Subterrestrial Muid convection: a hypothesis for long-distance migration of radon within the earth. Earth Plan. Sci. Lett. 34, 321–325. Massri, M., 1963. Report on the geology of the Amman-Zarqa area. Central Water Authority, Amman, pp. 1–74 (unpublished). Nero, A., 1990. Les contrˆoles de la pollution des logements. Pour la Sci. 129, 24–31. Nishimura, S., Katsura, I., 1990. Radon in soil gas: application in exploration and earthquake prediction In: Durrance, E.M. (Ed.), Geochemistry of Gaseous Elements and Compounds. The Ophrastus Publication, S.A. Athens, pp. 497–533. Varley, N.R., Flowers, A.G., 1998. Indoor radon prediction from soil-gas measurements. Health Phys. 74, 714–718.
www.elsevier.com/locate/radmeas
Radon anomalies along faults in North of Jordan M.H. Al-Tamimia; ∗ , K.M. Abumuradb a Department
of Earth and Environmental Sciences, Yarmouk University, PO Box 566, Irbid 211-63, Jordan of Physics, Yarmouk University, PO Box 566, Irbid 211-63, Jordan
b Department
Received 28 August 2000; received in revised form 27 November 2000; accepted 30 January 2001
Abstract Radon emanation was sampled in .ve locations in a limestone quarry area using SSNTDs CR-39. Radon levels in the soil air at four di3erent well-known traceable fault planes were measured along a traverse line perpendicular to each of these faults. Radon levels at the fault were higher by a factor of 3–10 than away from the faults. However, some sites have broader shoulders than the others. The method was applied along a .fth inferred fault zone. The results show anomalous radon level in the sampled station near the fault zone, which gave a radon value higher by three times than background. This study draws its importance from the fact that in Jordan many cities and villages have been established over an intensive faulted land. Also, our study has considerable implications for the future radon mapping. Moreover, radon gas is proved to be a good tool for c 2001 Elsevier Science Ltd. All rights reserved. fault zones detection. Keywords: Radon; Soil; Fault zones delineation; Plastic detectors
1. Introduction The use of radon as a geological tracer has been developed mainly in connection with uranium prospecting, environmental research, earthquake and volcanic prediction, thermoluminescence dating of ancient ceramics and fault zones con.rmation (King, 1980; Gingrich, 1984). Radon (222 R), an alpha emitting noble gas is produced in the radioactive decay series of uranium (238 U). It tends to migrate from its source mainly upwards. Its rate of migration and its soil-gas concentration are controlled by a large number of factors, such as the distribution of uranium in the soil and bed rock, soil porosity and humidity, microcracks, granulation, surface winds and so on. Durrani and Ili=c (1997) discussed the relation between geology and radon levels in groundwater, soil gas, and indoor air. Knowledge of the levels of radon in the soil gas and underground water or in the dwelling’s atmosphere is necessary to protect populations from the consequences of excessive exposure to radiation, for example from the risk of lung cancer (Nero, 1990). ∗ Corresponding author. Fax: +962-2-7274725. E-mail address: [email protected] (M.H. Al-Tamimi).
The amount of radon emitted from the earth crust into atmosphere is usually small. However unusual quantities of radon could be emitted above geological faults, geothermal sources, uranium deposits and volcanoes (Nishimura and Katsura, 1990). These anomalies of radon are subject to the emanation power of soils and rocks, to the mechanisms of migration and to the climate factors (Magro-Campero and Fleischer, 1977). In Jordan, radon emanations were measured in soils, rocks and indoor atmosphere in di3erent cities (Abumurad et al., 1997). Radium, the immediate precursor of radon gas, occurs virtually in all types of rocks and soils; its concentration varies from site to site and with the change of geological criteria. The present radon survey conducted in a quarry area located southwest of Irbid city in north Jordan, characterized by a homogenous lithology is expected to show similar radon emanation levels. However, the existence of fault zones in such locations would cause an increase in radon concentration along these faults. These fault zones are easily located and their attitudes can be measured through the quarry face. The color of the .lling materials along faulted zones becomes rosy to pale red due to the formation of di3erent iron oxides as a result of weathering
c 2001 Elsevier Science Ltd. All rights reserved. 1350-4487/01/$ - see front matter PII: S 1 3 5 0 - 4 4 8 7 ( 0 1 ) 0 0 1 9 3 - 7
398
M.H. Al-Tamimi, K.M. Abumurad / Radiation Measurements 34 (2001) 397–400
process of the crushed materials along these zones. The goals of the present work were to assure the suitability of this method to con.rm the existence of fault zones, to help in radon mapping and for epidemiological studies in Jordan.
four di3erent quarries. A .fth location was chosen where geomorphological criteria and geological map indicate an inferred fault. 3. Methodology
2. Geological setting The study area has a uniform thin soil cover. The underlying bedrock is characterized by uniform geophysical and geochemical properties such as porosity, mineral composition and almost homogenous thickness distribution (Bender, 1968, 1974). Moreover the bedrock in this area possesses a uniform lithology (Fig. 1) and belongs to one rock unit, which is called Wadi um Ghudran (WG) Formation (Massri, 1963). This rock unit consists of few meters of intercalations of soft white chalk and chalky limestone, which overlies a thick sequence of massive white hard limestone, that was called by Massri (1963) as Wadi Es-sir Formation. Fortunately, large number of limestone quarries in the area enabled us to easily locate fault zones and de.ne their attitudes in quarry face. However, the area under investigation is full of traceable and inferred faults. Four easily traceable, almost vertical faults were chosen from
Square pieces (1:5 cm × 1:5 cm) of solid-state nuclear track detectors (SSNTDs) CR-39 were mounted on the bottom of cylindrical plastic cans (Abumurad et al., 1994). The lid of each can is punched with few holes; these holes are then covered with thin (0:5 cm) pieces of sponge to .lter out 220 Rn. The resulted detectors were previously calibrated. Five holes of 50 cm depth were dug in each selected site and arranged in a line perpendicular to the fault trace: one hole, the third, lies on the fault zone, while two holes were located on the right- and on the left-hand side of the fault trace. The distance between adjacent holes was about 10 m. Furthermore, two detectors were put together upside down in each hole and then buried again. Planting of detectors was done with care so as not to disturb the soil cover in all sites. This work was carried out during August 1999. After 2 weeks the detectors were collected and chemically etched ◦ using 6N KOH at 70 C for 8:5 h. The density of alpha
Fig. 1. Map of the study area of Irbid city showing its geological criteria and locations of all sampled sites.
M.H. Al-Tamimi, K.M. Abumurad / Radiation Measurements 34 (2001) 397–400
tracks in the plastic detectors was counted using an optical microscope.
4. Results and discussions We assume that radon concentration should be similar in all measured holes as long as the depth of the detectors is constant, the type of soil is homogenous and the type of bed rock is the same all over the study area. Therefore, unusual increase in measured radon concentration should be related mainly to the existence of the fault zones. The rock along these zones are highly deformed and crushed to a great depth, which allows pathways for radon to migrate and di3use. The collected data from all sites and holes (samples) are displayed in Fig. 2. The radon concentration measured at two ends (i.e. No. 1, which is −20 m away from a fault and No. 5, which is 20 m on the other side of the fault) of each traverse is considered as background. The highest radon concentration value was recorded in the central sample (i.e. hole No. 3, which is 0 m from the fault), which is located almost over the fault zone. For example radon level increases as one goes along the traverse line from sample No. 1 to No. 2 to reach the maximum over sample No. 3 and then decreases again towards the other end of the traverse. The maximum value of radon level for a given site ranges from three to 10 times the minimum value of that site. In the .fth site of the inferred fault, radon concentrations have similar trend as in other sites. These radon concentration anomalies can be related to the expected changes of the properties of the rocks along
399
these fault zones. The rocks are crushed during faulting process. Therefore, faulting is usually accompanied with certain changes in its geological characteristics, such as a large increase in the porosity and permeability of the deformed rocks along these zones. Through this porous and permeable medium radon migrates upwards more easily (King, 1980; Kresl et al., 1993a, b). Besides, the crushed rocks along fault zones are also characterized by grain size reduction, which will a3ect also uranium-bearing minerals found in the rock body. This process will cause an increase in radon emanation (Gundersen and Linda, 1991). Furthermore oxidation of iron during faulting deformation and subsequent weathering, results in distinctive iron-staining nature of many fault zones. Iron oxides and other metal oxides scavenge uranium and radium available through the weathering processes. These processes increase the radon emanation from rocks and soils, and make radon readily available to local groundwater (Choubey and Ramola, 1997). Moreover, shoulders (i.e., radon levels in the samples just o3 the fault zone) of site 4 are broad, while that of site 5 are thin. This variation in shoulders among sites may be due to the thickness variations of fault zones. 5. Conclusion Radon sampling across faults has added to our understanding of how they vary spatially. This study is the .rst in Jordan to use “radon tool” to study the existence of fault zones in such locality. Highly localized variations in the radon levels on scale of several meters have been observed. Radon anomalies, of up to several thousands Bq=m3 , are not supported by local uranium. Radon levels over the fault zones are up to 10 times the background values. Using this tool with shorter distance between measuring samples (holes) one can estimate the width of the deformed fault zone just beneath thin soil layer covering this structure. This study draws its importance from the fact that in Jordan many cities and villages have been established over the western part of Jordan, which is an intensively faulted area located adjacent to the active transform Araba-Jordan rift. Moreover, applying this method will provide more information about faulted areas in Jordan and its radon distribution. It has been reported (Varley and Flowers, 1998) that levels as low as 10 kBq=m3 in the soil gas could produce an indoor radon concentration above the UK action level of 200 Bq=m3 . However, it is known that each 1 Bq=m3 of radon level means about 0:015 mSv=y (ICRP, 1993). So our results have considerable implications for the future of radon mapping and for epidemiological studies in Jordan.
References Fig. 2. Measured radon concentration values in soil gas.
Abumurad, K.M., Al-Bataina, B., Ismail, A., Kullab, M.K., Al-Eloosy, A., 1997. Survey of radon levels in Jordanian
400
M.H. Al-Tamimi, K.M. Abumurad / Radiation Measurements 34 (2001) 397–400
dwellings during an autumn season. Radiat. Prot. Dos. 69 (3), 221–226. Abumurad, K.M., Kullab, M.K., Al-Bataina, B.A., Ismail, A.M., Lehlooh, A.D., 1994. Estimation of radon concentrations inside houses in some Jordanian regions. Mu’tah J. Res. Stud. 9, 9–21. Bender, F., 1968. Geological map of Jordan. Bundesanst. Bodenforschung, Hannover. Bender, F., 1974. Geology of Jordan. Borntraeger, Stuttgart, p. 196. Choubey, V., Ramola, R., 1997. Correlation between geology and radon levels in groundwater, soil and indoor air in Bhilangana Valley, Garhwal Himalaya India. Environ. Geol. 32 (4), 258–268. Durrani, S.A., Ili=c, R. (Eds.), 1997. Radon Measurements by Etched Track Detectors: Application to Radiation Protection, Earth Sciences and the Environment. World Scienti.c, Singapore. Gingrich, J.E., 1984. Radon as geochemical exploration tool. J. Geophys. Explor. 21, 19–39. Gundersen, L.C.S., Linda, C.S., 1991. Radon in sheared igneous and metamorphic rocks. In: Gundersen, L.C.S., Wanty, R.B. (Eds.), Field Studies of Radon in Rocks, Soil and Water, US Geol. Survey Bull. 1991, 39 –50. ICRP, 1993. Protection against radon at home and at work. Ann. ICRP 65 (4), 5.
King, C., 1980. Episodic radon changes in subsurface soil gas along active fault and possible relation to earthquakes. J. Geophys. Res. 85 (B6), 3065–3078. Kresl, M., Vakova, V., Klecka, M., 1993a. Radon in soils overlaying several tectonic zones of the south Bohemian Moldanubicum. Jb. Geol. B. A. 136, Hf4, 799–808. Kresl, M., Vakova, V., Klecka, M., 1993b. Distribution of radon anomalies over the Choustnik fault zone (Central Bohemia). J. Czech Geol. Soc. 38, 225–233. Magro-Campero, A., Fleischer, R.L., 1977. Subterrestrial Muid convection: a hypothesis for long-distance migration of radon within the earth. Earth Plan. Sci. Lett. 34, 321–325. Massri, M., 1963. Report on the geology of the Amman-Zarqa area. Central Water Authority, Amman, pp. 1–74 (unpublished). Nero, A., 1990. Les contrˆoles de la pollution des logements. Pour la Sci. 129, 24–31. Nishimura, S., Katsura, I., 1990. Radon in soil gas: application in exploration and earthquake prediction In: Durrance, E.M. (Ed.), Geochemistry of Gaseous Elements and Compounds. The Ophrastus Publication, S.A. Athens, pp. 497–533. Varley, N.R., Flowers, A.G., 1998. Indoor radon prediction from soil-gas measurements. Health Phys. 74, 714–718.