IEG 환경지질연구정보센터

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(1)CSIRO PUBLISHING www.publish.csiro.au/journals/eg. Copublished paper, please cite all three:. Exploration Geophysics, 2010, 41, 61–68; Butsuri-Tansa, 2010, 63, 61–68; Jigu-Mulli-wa-Mulli-Tamsa, 2010, 13, 61–68. Magnetotelluric survey applied to geothermal exploration: An example at Seokmo Island, Korea* Tae Jong Lee1,3 Nuree Han2 Yoonho Song1 1. Korea Institute of Geoscience and Mineral Resources (KIGAM), Gajeong-dong 30, Yuseong-gu, Daejeon 305-350, Korea. 2 Seoul National University, 599 Gwanak-ro, Gwanak-gu, Seoul 151-742, Korea. 3 Corresponding author. Email: [email protected]. Abstract. A magnetotelluric (MT) survey has been performed to delineate deeply extended fracture systems at the geothermal field in Seokmo Island, Korea. To assist interpretation of the MT data, geological surveying and well logging of existing wells were also performed. The surface geology of the island shows Cretaceous and Jurassic granite in the north and Precambrian schist in the south. The geothermal regime has been found along the boundary between the schist and Cretaceous granite. Because of the deep circulation along the fracture system, geothermal gradient of the target area exceeds 45C/km, which is much higher than the average geothermal gradient in Korea. 2D and 3D inversions of MT data clearly showed a very conductive anomaly, which is interpreted as a fracture system bearing saline water that extends at least down to 1.5 km depth and is inclined eastwards. After drilling down to the depth of 1280 m, more than 4000 tons/day of geothermal water overflowed with temperature higher than 70C. This water showed very similar chemical composition and temperature to those from another existing well, so that they can be considered to have the same origin; i.e. from the same fracture system. A new geothermal project for combined heat and power generation was launched in 2009 in Seokmo Island, based on the survey. Additional geophysical investigations including MT surveys to cover a wider area, seismic reflection surveys, borehole surveys, and well logging of more than 20 existing boreholes will be conducted. Key words: fracture system, geothermal, magnetotelluric survey, Seokmo Island.. Introduction Korea does not have a high-temperature geothermal regime. There is no active volcano in Korea and there have been no volcanic or major tectonic activities for more than a thousand years. Historical literature says that the last volcanic activity was observed a thousand years ago (1007 AD) in Jeju Island, the only volcanic island in Korea (Lee, 1985). Nevertheless, there are many hot springs and people have used hot spring water for bathing for more than thousand years. However, the temperature of those hot springs is not high enough to be used for power generation or district heating; the highest one so far is only 78C in the Bugok hot spring, which is located in the south-eastern part of the Korean Peninsula. Most hot springs in Korea are closely related to deeply extended fracture systems in crystalline rock such as Cretaceous or Jurassic granite. The geothermal regime in Seokmo Island is no exception and was initially reported by hot-spring developers. They happened to find a geothermal anomaly there without detailed scientific investigations while drilling several hundred metres to develop hot water. From one of the wells (BH-1), a great amount of geothermal water at ~70C overflows, while the other well (BH-2) failed to strike geothermal water, although it reached a depth of 1200 m. The two wells are separated by only ~350 m from each other. To figure out the reason and to delineate the fracture systems as well as geological structures at depth, in this study, geological mapping of the island, geophysical surveys including magnetotelluric (MT), audio-frequency MT (AMT). surveys and well logging, and geochemical investigations have been performed. Geological settings The geology of Seokmo Island is characterised by outcrops of basement rocks, and consists mainly of Precambrian schist and granite gneiss, medium-grained Jurassic granites, and fineto medium-grained Cretaceous granites. Some parts of the island are covered by very thin (<20 m) Quaternary sediments (Figure 1). One can divide the island into three parts according to the geology; Jurassic granite is mainly found in the northern part (north rock body), Cretaceous granite in the south (south rock body), and Precambrian schist in the west and south of the island. Rb-Sr ages of the granites are 132 50 Ma for the south rock body and 207 70 Ma for the north rock body (Lee et al., 2006a). The main target area, where most of drill-wells are located in Figure 1, is along the boundary between the schist (Jangbong Schist) in the south and Cretaceous granite in the north. Note that the orientation of vertical joints, which has been analysed from outcrops over the islands and is displayed on the bottomright corner of Figure 1, is mainly in the direction of NNE and WNW. The distribution pattern of vertical joints will be related to deep seated-fracture systems, to the history of geological activity, and to the paleostress fields of the area. Note that a lineament that can be identified from the topography, marked by a. *Part of this paper was presented at the 9th SEGJ International Symposium (2009).. ASEG/SEGJ/KSEG 2010. 10.1071/EG10001. 0812-3985/10/010061.

(2) 62. Exploration Geophysics. T. J. Lee et al.. Fig. 1. Geological map of Seokmo Island. A rose diagram of vertical joint orientations, measured from outcrops, is displayed as well. The blue solid line indicates a lineament of interest (Modified from Park and Lee, 2007).. solid line in the figure, runs in the NNE direction and is identical in direction to the major orientation of joints of the area. Geophysical surveys More than 20 deep wells for developing hot spring water have been drilled so far within the island, especially near the south rock body, which was formed by the most recent intrusion during the Cretaceous period (Figure 1). A few of the wells can produce hot water with temperature ranging over 62–72C from depths. between 750 and 1000 m, but most of them failed to get enough flow. Figure 2 shows temperature logs for the boreholes BH-1 and BH-2 shown in Figure 1, natural gamma-ray logs, and a lithologic column for BH-2. The temperature profile for BH-1 shows higher than 65C from the surface, because of overflowing geothermal water. However, the temperature profile for well BH-2 shows a typical conductive regime. There is not enough flow. Note that temperature profile for BH-2 is perturbed slightly at the depth of 830 m, which indicates a permeable zone, where the boundary.

(3) Magnetotelluric survey at Seokmo Island. Exploration Geophysics. 63. Fig. 2. Temperature logs for the boreholes BH-1 and BH-2, and natural gamma-ray log of BH-2 compared with the lithologic column.. interpretation of this abnormal geothermal gradient would be deep circulation of sea water along deeply extended fracture systems, which is a most common feature in hot spring areas in Korea; i.e. convection of hot water from deeper parts heats up the formations near the surface.. 466 000. between an acid dyke and biotite granite is located. The geothermal gradient estimated from the BH-2 temperature log is greater than 45C/km. When compared with the average geothermal gradient in Korea (25.1C/km; Kim and Song, 2005), this is an abnormal value. The most likely. 301. 219. 464 000. 217 304 215. 112. D 3-. 305 111. in. 109. r te. 306 108. e pr t ta n io. Northing (m). 302. 101 309 102 110 209 311 107 103 312 106 207 104 313 105 115 205. 462 000. 203. 138 000. 116 113 118 114 117. BH-2. 119 315. 317. Li. ne. -Y. Li n. e-X. 201. MT sites Boreholes. BH-1. 307. 140 000. 142 000. 144 000. Easting (m) Fig. 3. Target area and site map of MT and AMT surveys. The locations of boreholes are superimposed..

(4) 64. Exploration Geophysics. T. J. Lee et al.. (a). (b) 103 Rx-207. Rx-205. 10. App. Res. (Ω.m). App. Res. (Ω.m). 103 Zxy Zyx. 2. 101 100. Zxy Zyx. 101 100 10–1 180. Phase (degree). 10–1 180. Phase (degree). 10. 2. 90 0 –90. 90 0. –90. –180. –180 105. 103. 101. 105. 10–1. 103. Frequency (Hz) (c). 103. 102. Rx-313. App. Res. (Ω.m). Rx-209. App. Res. (Ω.m). 10–1. (d ). 103 Zxy Zyx. 101 100. Zxy Zyx. 102 101 100 10–1 180. Phase (degree). 10–1 180. Phase (degree). 101. Frequency (Hz). 90 0 –90 –180. 90 0. –90. –180 104. 102. 100. 104. 102. Frequency (Hz). 100. 10–2. Frequency (Hz). Fig. 4. AMT and MT sounding curves for the sites (a) 205, (b) 207, (c) 209, and (d) 313.. To understand the fracture system that possibly acts as a conduit of the geothermal water, a MT survey and an AMT survey have been carried out in conjunction with each other. The use of AMT data in MT interpretation can greatly improve the resolution of the shallow part of the survey area, and thus can help in resolving deeper parts as well (Lee et al., 2006b). MT measurement sites are shown in Figure 3. A total of 39 measurements were made using Phoenix MTU-5A systems. Since it is not easy to access the mountains carrying heavy MT equipment, most measurements have been made in rice fields, where the topography is almost flat. Unfortunately, however, the survey area is extremely noisy. There are a lot of electromagnetic noise sources; power lines cover the whole rice field area, on/off noises from groundwater pumps and from houses very near to the sites, and cars. The overall noise level is too high, so that low frequency MT data below 1 Hz could not be obtained even though remote reference processing (Gamble et al., 1979) has been applied. Data from a permanent monitoring station in Esashi, Japan, which is more than 1500 km distant from the sites, are used for remote reference processing for MT data. The remote reference for AMT processing is the data obtained from the other field site at the same time. Figure 4 shows example of typical sounding curves. Here x points to the north. Note that splits between apparent resistivity. 340. 350. 0. 10. 20. 330. 30. 320. 40. 310. 50. 300. 60. 290. 70. 280. 80. 270. 90 0. 10. 20. 30. 40. 50. 260. 100. 250. 110. 240. 120 230. 130 220. 140 210. 150 200. 190. 180. 170. 160. Fig. 5. Rose diagram for strike directions estimated from MT impedance tensors..

(5) Magnetotelluric survey at Seokmo Island. Exploration Geophysics. the figure that N30E and N40–50W are dominant over the survey region. In theory, the estimated direction has intrinsic rotational ambiguity of 90 degrees (Geotools Corporation, 1997). Major strike direction of the basement rocks can therefore be either N30E or N60W, which is consistent with the orientation of vertical joints observed on the surface as shown in Figure 1. Considering the major direction of the lineament distribution described in Figure 1, and the estimated strike direction shown in Figure 5, 2D interpretations for the two survey lines (Line-X and. curves in orthogonal directions, electric field to the north (Zxy) and to the east (Zyx), indicate 2D or 3D structures beneath the area. Note also that the data suffers severe static shifts; the apparent resistivity at site 209 at the highest frequency, for example, is almost 10 times higher than the others. Figure 5 shows a frequency diagram of estimated strike direction from measured MT impedance tensors, which is the angle that maximizes the difference between impedances in the two directional components (Zxy versus Zyx). One observes from. 1000. Rx207. 1000. Rx305. Rx307. Rx311 10 000. 100. 100. 100. 1000. 10 10. 10 100. 1. 0.1. 1. 10. 100. 1000. 10. 1. 0.1. 1. 1. 10. 100. 1000. 0.1. 1. 10. 100. 1000. 90. 90. 90. 90. 60. 60. 60. 60. 30. 30. 30. 30. 0. 0 0.1. 1. 10. 100. Rx315. 10. 100. 1000. 0.1. Rx102. 100. 1. 10. 100. 1000. Rx104. 1000. 10. 0.1. 1. 10. 100. 1000. 0.1. 1. 10. 100. 1000. 0.1. 1. 10. 100. 1000. 0.1. 1. 10. 100. 1000. 0. 0 1. 1000. Rx106. 1000. 1000. 100. 100. 10. 10. 100 1 0.1. 10 0.1. 1. 10. 100. 1000. 1. 1 0.1. 1. 10. 100. 1000. 0.1. 1. 10. 100. 1000. 90. 90. 90. 90. 60. 60. 60. 60. 30. 30. 30. 30. 0. 0 0.1. 1. 10. 100. 1000. Rx108. 1. 10. 100. 1000. 100. 10. 10. 1 1. 10. 100. 1000. 1. 10. 100. Rx113. Rx115 100. 100. 10. 10. 1. 1 0.1. 1000. 1000. 1 0.1. 0.1. Rx110. 100. 0. 0 0.1. 1. 10. 100. 1000. 1. 10. 100. 0.1 1000 1. 90. 90. 90. 90. 60. 60. 60. 60. 30. 30. 30. 30. 0. 0 0.1. 1. 10. 100. 1000. Rx117. 1. 10. 100. 1000. 10. 100. 1000. 10. 100. 1000. 0. 0 0.1. 1. 10. 100. 1000. 1. Rx119. 100. 100. 10 10 1. Zxy mode: observed Zyx mode: observed. 0.1. 1 1. 10. 100. 1000. 90. 90. 60. 60. 30. 30. 0. Zxy mode: calculated 1. 10. 100. 1000. 1. 10. 100. 1000. Zyx mode: calculated. 0 1. 10. 100. 1000. 65. Fig. 6. Fit between measured data (symbols) and 3D inversion model responses at final iteration (lines)..

(6) Exploration Geophysics. T. J. Lee et al.. Line-Y) were performed using a damped least-square inversion scheme based on a finite element forward code (Uchida, 1993). For the 2D inversion, 52 frequencies from 0.293 to 4400 Hz at logarithmic spacing were used. Data with high measurement error were excluded for the inversion, so that very few sites have data at frequency below 1 Hz. For Line-X, for example, only one site (site 203) has data at the lowest frequency (0.293 Hz); data from the other sites are discarded because of large measurement error. A 3D inversion with static shift parameterization (Han et al., 2008) was also performed for the area surrounded by a rectangle in Figure 3. For the 3D inversion, 11 frequencies from 0.43 to 229 Hz at logarithmic spacing were used. Topography was not considered in either the 2D or 3D inversions, but the 3D inversion does incorporate static shifts compensation (Han et al., 2008).. BH–2. Depth (m). –500. Line-Y(TM). West 301. 215 217219. –500. –1000. –1000. –1500. –1500. East. 302 304 305 306 307 309 311312 313 315 317. 0. BH–1. 201 203 205 207 209309. 0. North. BH–2. Line-X(TM). South. Unlike the 2D inversion, the 3D inversion incorporates static shifts into the inversion and so it can be assumed that static shifts have been compensated during the inversion. Very strong static shift, which exceeded several times at several sites, were removed during the inversion. Because of the strong electromagnetic noise, the 3D inversion does not converge adequately. The root-meansquare (rms) misfit decreased to 3.66 at the final (10th) iteration from an initial rms value of 12.89. Figure 6 shows the model curve fits at alternate sites among the 28 measurement sites. The inversion generally seems to experience more difficulty in fitting the phase than the apparent resistivity, although the same weights between the two are applied in the inversion. Figure 7 compares the inversion results. In Line-X (TM), a boundary in the shallow part (<500 m) can be seen to divide. BH–1. 66. –2000. –2000 0. 500. 1000. 1500. 2000. 0. 2500. 500. 1000. 1500. Distance (m). 2000. 2500. 3000. 3500. 4000. Distance (m). Line-Y(3D). 0. 1. 2. 3. BH–2. –500. BH–1. 0. –1000. Log resistivity (Ω.m) –1500 –2000. Fig. 7. Resistivity images from 2D (TM mode) and 3D inversion of MT data for survey lines, Line-X and Line-Y, and the area surrounded by a rectangle, respectively, in Fig. 3.. Fig. 8. Drilling rig (left) and overflowing geothermal water from BH-2 (right)..

(7) Magnetotelluric survey at Seokmo Island. Exploration Geophysics. Table 1. Comparison of chemical composition of geothermal waters from BH-1 and BH-2. Major elements. Concentrations in mg/L BH-1 BH-2. K Na Cl Mg SiO2 SO4 Sr Ca. 85.6 4815 12 100 251 54.4 970 76.39 3489. 80.0 4441 12 100 233 48.6 970 72.30 3240. conductive south from resistive north. Basement is found at the surface in the northern part of Line-X, while shallow fracture systems, with seawater intrusion, are to be expected in the southern part of Line-X. At depth, a conductive discontinuity can be seen beneath stations 207 and 209. The two boreholes are in the margin of this discontinuity. In Line-Y (TM), one can find a very strong conductive anomaly at 500–1500 m depths and extending deeper. This could be the fracture system that carries geothermal water in BH-1. Geothermal water produced from BH-1 is saline water with conductivity of 49 000 mS/cm. Saline water along a fracture system is assumed to form such a strong conductivity anomaly and BH-2 is projected to meet the fracture system in the resistivity image. This is much clearer when comparing the two conductivity images from 2D and 3D inversions in Figure 7. In Line-Y (3D), the boundary between conductive and resistive zones appears more clearly and one can see that the boundary inclines to the east. If this boundary is related to the fracture system that carries geothermal water to BH-1, then BH-2 is already very close to the depth of the fracture system. With these promising interpretations, additional drilling for BH-2 was decided, and it eventually met the fracture system after drilling 80 m more. More than 4000 tons/day of geothermal water at a temperature of 70C now overflows from BH-2 (Figure 8). Chemical composition of geothermal water from BH-1 and BH-2 is almost the same (Table 1). Geothermal water from the two boreholes shows similar temperature and chemical composition, so that they can be considered to have the same origin; i.e. from the same fracture system. Note from Table 1 that the geothermal water contains a large amount of sodium and chlorine. Conclusions Preliminary geological and geophysical surveys have been carried out for deep geothermal development in Seokmo Island, Korea. Basement rocks, mainly Precambrian schist and Jurassic or Cretaceous granites can be found close to or even at the surface. In these crystalline formations, the most likely scenario is that the geothermal regime can be attributed to deep circulation of seawater along the fracture systems. MT surveys, geophysical well logs, and drilling results support this scenario.. 67. The MT method can be a very useful tool for mapping subsurface fracture systems as well as geoelectrical structures at depth. Unfortunately at this site, however, artificial electrical noise level is too high due to residences nearby, power lines, and groundwater pumps, so that MT data below 1 Hz cannot be obtained. Using MT and AMT data for frequencies above 1 Hz, 2D and 3D inversions give reasonable images of subsurface conductivity structures down to roughly 2 km. In 2009, Korea Institute of Geoscience and Mineral Resources (KIGAM) have launched a new geothermal project in Seokmo Island. The purpose of the project is to develop deep geothermal water of over 95C within 3 km depth and to utilise the geothermal water for combined heat and power generation. This year, the first year of the project, additional geophysical investigations will be carried out to get detailed information on deep geological structures. These investigations include additional MT surveys to cover a wider area, and seismic reflection surveys, borehole surveys, and well logging in more than 20 existing boreholes. Acknowledgments This work was supported by Basic Research Project of Korea Institute of Geoscience and Mineral Resources (KIGAM) and the Ministry of Land, Transport and Maritime Affairs through the project “Development of Marine Hydrothermal Mineral Deposits”. We thank the Geomagnetic Survey Institute (GSI) of Japan for providing the magnetotelluric monitoring data.. References Gamble, T. D., Goubau, W. M., and Clarke, J., 1979, Magnetotelluric with remote reference: Geophysics, 44, 53–68. Geotools Corporation, 1997, Geotools MT user’s guide – A complete system for magnetotelluric interpretation: Geotools Corporation. Han, N., Nam, M. J., Kim, H. J., Lee, T. J., Song, Y., and Suh, J. H., 2008, Efficient three-dimensional inversion of magnetotelluric data using approximate sensitivities: Geophysical Journal International, 175, 477–485. doi:10.1111/j.1365-246X.2008.03894.x Kim, H.-C., and Song, Y., 2005, Characteristics of Geothermal Anomaly in South Korea: Proceedings, World Geothermal Congress, Antalya, Turkey, 24–29 April. Lee, M. W., 1985, Jeju volcanic Island: Journal of Korean Earth Science Society, 6, 49–53. Lee, S.-G., Kim, T.-K., Lee, J.-S., and Song, Y., 2006a, Rb-Sr Isotope geochemistry in Seokmodo granitoids and hot spring, Ganghwa: An application of Sr isotope for clarifying the source of hot spring: Journal of Petroleum Society of Korea, 15, 60–71. Lee, T. J., Lee, S. K., Song, Y., and Uchida, T., 2006b, Use of Audio-band on the interpretation of magnetotelluric data: Mulli-Tamsa, 9, 261–270. Park, D.-W., and Lee, C.-B., 2007, Characteristics of micro-crack orientations in Mesozoic granites and granite dyke rocks from Seokmo-do, Ganghwagun: Journal of Petroleum Society of Korea, 16, 1–15. Uchida, T., 1993, Smooth 2-D inversion for magnetotelluric data based on statistical criterion ABIC: Journal of Geomagnetism and Geoelectricity, 45, 841–898.. Manuscript received 23 November 2009; accepted 14 December 2009..

(8) 68. Exploration Geophysics. T. J. Lee et al.. 沖匶滆洊幞憛汊͑ 決殯穢͑ 昣微壊櫖昢汞͑ 滆櫺沖毖͑ 痖斲͑ 㧊䌲㫛1, 䞲⑚Ⰲ2, ㏷㥺䢎 1 1 䞲ῃ㰖㰞㧦㤦㡆ῂ㤦G 2 ㍲㤎╖䞯ᾦ . 殚͑ 檃౐G Ⱂㄶ❶ Ⴏ㫮ሊ ▷ὂᡞ⯲ ⹚⪎⩪ᖢ⹚ Ⴖ₶⯞ ⮞㧲⪆ ➆√ 㞦♞រ 㨎▷⯞ ⮞㧶 MT 㕪╆Ḗ ⚲㨣㧲⪚᝾. ᪪㧶, MT 㕪╆Ⱚᵦ⯲ 㨎▷⯞ ⮞㨎▶, ⹚⹢ⴊ╆⫚ ➆√❶㈮ᆏ ῖṆᄚ㋏⯞ 㨂፲ ⚲㨣㧲⪚᝾. ▷ὂᡞ⯲ ⹚⹢⯚ ∛⽗⩪ᜮ ⃋⧟ዊ⫚ ⸆ᰖዊ⩪ ᆚⰟᢶ 㫮Ⴏ⧮Ⰾ, ᕂ⽗⩪ᜮ ►㌞⊦Ṇ⧞ዊ⯲ 㡒⧮ᷲႚ ∞㢆㧶᝾. Ⰾ ⹚⪇⩪▶ ⹚⪎⹯㭞ᜮ 㡒⧮ᷲ⫚ ⃋⧟ዊ⯲ 㫮Ⴏ⧮⯲ ᅗᅞ√⩪▶ ₶ᅆᢲ⩢᝾. ➆√㞦♞រḖ ᧊Ḓ ⪎⚲⯲ ⚶㫲⩪ ⯲㨎 រ╛⹚⪇⯲ ⹚⫂⸷ႚ⯂⯚ 45°C/km Ⰾ╛⯖ᳶ រ㧶ₖሇ 㡣ቺ↎᝾ 㮂⧆ ᘬᄦ ᔲ㕚ᕆ᝾. MT 㕪╆Ⱚᵦ⯲ 2ヂ⭪ ₩ 3ヂ⭪ 㨎▷ ᅊᆖ, ⲞዊⲞᡞᡞႚ Ṿ⭊ ᘬ⯚ Ⰾ╛រႚ ᡳ⽗⯖ᳶ ᅗ╆Ⳓ▶ ⹚㧲 1.5 km ዤⰎዦ⹚ ∞㢆㧲ᜮ ᄝ⯖ᳶ ᔲ㕚ᕆ⯖Ἂ Ⰾᜮ 㨎⚲ᳶ マ⭦⹞ 㞦♞រᳶ 㨎▷ᢲ⩢᝾. Ⰾ Ⰾ╛រḖ ὃ㣶ᳶ ❶㈮㧶 ᅊᆖ1280 m➆ᡞ⩪▶ ⰖⰖ 4000 ton Ⰾ╛, ⫂ᡞ 70°C Ⰾ╛⯲ Ṩ⯚ ⨫⯲ ⹚⪎⚲Ḗ Ⴖ₶㧲ᜮ᠊ ○ᆏ㧲⪚᝾. Ⰾ ⹚⪎⚲⯲ 㫮㧳ⲛⰒ ○∞⯚ ዊⴎ ❶㈮ᆏ⩪▶ ₶ᅆᢶ ⹚⪎⚲⯲ 㫮㧳○∞ᆖ Ṿ⭊ ⮺╆㧲⪆ ᡳⰖ㧶 ⹚⪎Ⲛᷲ㋏, ⸣, ᡳⰖ㧶 ⹚⪎Ⲛᷲ㋏⩪▶ ╷╊ᢲᜮ ᄝ⯖ᳶ ႞ⶖ㧺 ⚲ Ⱒ⯞ ᄝ⯖ᳶ 㞪គ㧲⪚᝾. Ⰾᲆ㧶㕪╆ᅊᆖḖ ዊㆢᳶ 2009ᗞ√㗊㧶ሇ⹚⹢Ⱚ⭪⪊ሆ⭪⩪▶ᜮ ⹚⪎ ⪎Ⅻ㨃 ₶Ⲟ⯞ ⮞㧶 ╢ᳶ⭎ ⹚⪎Ⴖ₶ 㦞ᳶⲷ㝒Ḗ ❶Ⱛ㧲⪚ᅺ ㈮ႚⲛⰒ MT 㕪╆⫚ 㕞○㞦 ₲╆ℯ 㕪╆, Ⰾₒ ሎッᢲ⩎ Ⱒᜮ 20⪆Ⴖ⯲ ➆√ ❶㈮ᆏ⩪ រ㧲⪆ ῖṆᄚ㋏⯞ 㢆㨂㧶 ႛⴟ ❶㈮ᆏ ⴊ╆ ᦋⰎ ⚲㨣 ⶫⰎ᝾. 渂殚檺౐㰖㡊SG 㧦₆㰖㩚⮮䌦㌂SG 䕢㐚╖SG ㍳⳾☚G G. /6 ᴺߩ࿾ᾲ⾗Ḯតᩏ߳ߩㆡ↪̆㖧࿖ᏨᲫፉߦ߅ߌࠆ଀ ᧘ ᵏ㎠1࡮㖧 ࠿࡝2࡮ቡ మ㎼1 1 㖧࿖࿾⾰⾗Ḯ⎇ⓥ㒮 2 ࠰࠙࡞࿖┙ᄢቇᩞ . ⷐ ᣦ㧦㖧࿖ᏨᲫፉ㧔࠰ࡕࡦ࠼㧕ߩ࿾ᾲ࿾ၞ߅޿ߡᷓㇱߩᢿⵚ♽ࠍᛠីߔࠆߚ߼ߦ‫ޔ‬MT ᴺ⺞ᩏࠍታᣉߒߚ‫⚿ߦࠄߐޕ‬ᨐߩ ⸃㉼ߩߚ߼ߦ‫ޔ‬࿾⴫࿾⾰⺞ᩏߣᣢሽဒ੗ߢߩᬌጀ߽ታᣉߒߚ‫ޕ‬ᏨᲫፉߩ⴫ጀ࿾⾰ߪ‫ޔ‬ർㇱߢߪ⊕੝♿߅ࠃ߮ࠫࡘ࡜♿ߩ⧎ፘጤ‫ޔ‬ ධㇱߢవࠞࡦࡉ࡝ࠕ♿ߩ ጤ߆ࠄ᭴ᚑߐࠇߡ޿ࠆ‫ޕ‬࿾ᾲ♽ߪ ጤߣ⊕੝♿ߩ⧎ፘጤߣߩႺ⇇ߦᴪߞߡ⷗ߟ߆ߞߡ޿ࠆ‫ޕ‬ᢿⵚ♽ ߦᴪߞߚᷓㇱ߆ࠄߩᾲ᳓ᓴⅣߩߚ߼‫ޔ‬ኻ⽎ࠛ࡝ࠕߢߪ᷷ᐲ൨㈩߇‫ޔ‬㖧࿖ߦ߅ߌࠆᐔဋ᷷ᐲ൨㈩ࠃࠅ߆ߥࠅᄢ߈޿ 45͠/km ߣߥ ߞߡ޿ࠆ‫ޕ‬MT ᴺ࠺࡯࠲ߩ㧞ᰴర߅ࠃ߮㧟ᰴరㅒ⸃ᨆ⚿ᨐߦߪ‫ޔ‬᣿⍎ߥ㜞㔚᳇વዉᐲ⇣Ᏹ߇᛽಴ߐࠇ‫ߪࠇߘޔ‬Ⴎ᳓ߢḩߚߐࠇ ߚᢿⵚ♽ߣ⸃㉼ߐࠇࠆ‫⇣ߩߘޕ‬Ᏹߪዋߥߊߣ߽ᷓᐲ 1.5km ߹ߢਅᣇߦᑧ߮‫᧲ޔ‬஥ߦ௑޿ߡ޿ࠆ‫ޕ‬ᷓᐲ 1280m ߹ߢߩࡏ࡯࡝ࡦ ࠣជ೥ߩ⚿ᨐ‫ޔ‬㧝ᣣ޽ߚࠅ 4000 ࠻ࡦએ਄ߩ 70͠એ਄ߩ࿾ᾲᵹ૕߇⥄ྃߒߚ‫ߩߎޕ‬࿾ᾲᵹ૕ߩൻቇ⚵ᚑ߿᷷ᐲߪ‫ߩઁޔ‬ᣢሽဒ ੗ߣ㕖Ᏹߦ㘃ૃߒߡ޿ࠆߩߢ‫ߪࠄࠇߘޔ‬ห৻⿠Ḯ‫ߜࠊߥߔޔ‬ห৻ߩᢿⵚ♽⿠Ḯߢ޽ࠆߣ⠨߃ࠄࠇࠆ‫⺞ߩߘޕ‬ᩏ⚿ᨐࠍ߽ߣߦ‫ޔ‬ ᏨᲫፉߢߪ‫ޔ‬2009 ᐕߦᾲߣ⊒㔚ࠍ⚿วߒߚᣂⷙ࿾ᾲࡊࡠࠫࠚࠢ࠻߇ᆎ߹ߞߚ‫ࠅࠃޕ‬ᐢ▸࿐ߥ࿾ၞࠍᛠីߔࠆߚ߼ߩ MT ᴺ⺞ ᩏ‫ޔ‬෻኿ᴺ࿾㔡តᩏ‫ޔ‬ဒ੗⺞ᩏ‫ޔ‬20 ᧄએ਄ߩᣢሽဒ੗ߢߩᬌጀࠍ฽ࠎߛㅊടߩ‛ℂតᩏ⺞ᩏ߇ታᣉߐࠇࠆ੍ቯߢ޽ࠆ‫ޕ‬ ࠠ࡯ࡢ࡯࠼㧦ᢿⵚ♽࿾ᾲ/6 ᴺ⺞ᩏᏨᲫፉ. http://www.publish.csiro.au/journals/eg.

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