{"title":"Pictorial 2: Results of the Laser Scanner and the CSAMT Surveys Carried out in the Kamou Area, Tokamachi City, Niigata Prefecture","authors":"Koichi Suzuki, Shingo Tokuyasu, Sakae Mukoyama, Kazuhiro Tanaka","doi":"10.5026/jgeography.118.xiv","DOIUrl":"https://doi.org/10.5026/jgeography.118.xiv","url":null,"abstract":"","PeriodicalId":356213,"journal":{"name":"Chigaku Zasshi (jounal of Geography)","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-07-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133690255","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2009-04-25DOI: 10.5026/jgeography.118.309
T. Kanamaru
In August 2008, I visited some rift zones, volcanoes, and glaciers in Iceland, and was impressed with Iceland's nature and Icelandic activities for harnessing it. I would like to introduce you to some of the geological tourist attractions in Iceland.
{"title":"Geological Resources for Tourism in North and South Iceland","authors":"T. Kanamaru","doi":"10.5026/jgeography.118.309","DOIUrl":"https://doi.org/10.5026/jgeography.118.309","url":null,"abstract":"In August 2008, I visited some rift zones, volcanoes, and glaciers in Iceland, and was impressed with Iceland's nature and Icelandic activities for harnessing it. I would like to introduce you to some of the geological tourist attractions in Iceland.","PeriodicalId":356213,"journal":{"name":"Chigaku Zasshi (jounal of Geography)","volume":"425 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122813018","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We analyzed core samples from two sites in the Tokyo lowland to clarify paleoenvironmental changes that occurred during the Holocene in the northern Tokyo Bay area. The samples are from (1) Core HK, which was bored at Hibiya Park, Chiyoda Ward, Tokyo, and from (2) Core DK, which was bored at Civil Engineering Center Tokyo Metropolitan Government in Koto Ward, Tokyo. Both cores belong to Civil Engineering Center Tokyo Metropolitan Government. Analyses of both lithofacies and diatom assemblages of the cored samples found the following paleoenvironmental changes. The first distinct regression occurred in the early Holocene (11,450-10,600 cal. yrBP) and was followed by one in the high-stand relative sea-level stage at 7,300-6,250 cal. yrBP. Subsequently, two small-scale regressions occurred at 3,600-1,200 cal. yrBP and 1,000 cal. yrBP, respectively. These two regressions were documented by temporal variations in diatom assemblages from marine to brackish-water diatoms to brackish and fresh-water diatoms. During the high-stand stage (7,300-6,250 cal. yrBP), the Hibiya embayment area was inundated with seawater and became part of Paleo-Okutokyo Bay. The marine transgressions and regressions inferred from diatom assemblages in both cores might be correlated with small-scale sea-level fluctuations at one- or two-thousand-year intervals during the Holocene, such as a minor regression during the middle Jomon period, Yayoi regression, and Heian transgression.
{"title":"Reconstruction of the Holocene Environments in the Tokyo Lowland, Inferred from Diatom Assemblages","authors":"Ishikawa Satoshi, 智 石川, Suzuki Takehiko, 毅彦 鈴木, 俊雄 中山, Nakayama Toshio, K. Kaoru, 薫 鹿島","doi":"10.5026/JGEOGRAPHY.118.245","DOIUrl":"https://doi.org/10.5026/JGEOGRAPHY.118.245","url":null,"abstract":"We analyzed core samples from two sites in the Tokyo lowland to clarify paleoenvironmental changes that occurred during the Holocene in the northern Tokyo Bay area. The samples are from (1) Core HK, which was bored at Hibiya Park, Chiyoda Ward, Tokyo, and from (2) Core DK, which was bored at Civil Engineering Center Tokyo Metropolitan Government in Koto Ward, Tokyo. Both cores belong to Civil Engineering Center Tokyo Metropolitan Government. Analyses of both lithofacies and diatom assemblages of the cored samples found the following paleoenvironmental changes. The first distinct regression occurred in the early Holocene (11,450-10,600 cal. yrBP) and was followed by one in the high-stand relative sea-level stage at 7,300-6,250 cal. yrBP. Subsequently, two small-scale regressions occurred at 3,600-1,200 cal. yrBP and 1,000 cal. yrBP, respectively. These two regressions were documented by temporal variations in diatom assemblages from marine to brackish-water diatoms to brackish and fresh-water diatoms. During the high-stand stage (7,300-6,250 cal. yrBP), the Hibiya embayment area was inundated with seawater and became part of Paleo-Okutokyo Bay. The marine transgressions and regressions inferred from diatom assemblages in both cores might be correlated with small-scale sea-level fluctuations at one- or two-thousand-year intervals during the Holocene, such as a minor regression during the middle Jomon period, Yayoi regression, and Heian transgression.","PeriodicalId":356213,"journal":{"name":"Chigaku Zasshi (jounal of Geography)","volume":"386 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-04-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"123391275","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2009-04-07DOI: 10.5026/JGEOGRAPHY.118.969
H. Nakagawa, Maki Suzuki, E. Takeuchi, R. Matsumoto
Plantonic and benthic foraminifera are analyzed with 11 sediment cores recovered from the Umitaka Spur area of the Joetsu Basin off Joetsu, Niigata Prefecture. The area is characterized by active methane seeps and methane hydrates. We recognize 12 foraminiferal biozones (Biozone I to XII in descending order) in the last 32000 years based on three selected cores (two well-dated and one longest), and apply them to another 8 cores for correlation. Sediment cores are divided into five lithologic units as massive to bioturbated mud (lithologic unit 1), thinly laminated mud (unit 2), gray massive mud (unit 3), thinly laminated dark mud (unit 4), and bioturbated mud (unit 5) from upper to lower. Lithologic units 2 and 4 correspond to basin-wide thinly laminated layers, previously reported as TL-1 and TL-2, respectively. The Japan Sea became a closed inland basin during the lowest sea level period of the last glacial maximum (LGM) at 27-26cal kyr BP (Biozone VIII). The surface water reached the lowest salinity level, while the bottom water was strongly anoxic due to reduced vertical circulation. An expulsion of a large amount of methane occurred on the Umitaka Spur during the LGM due to a massive dissociation of subsurface methane hydrate. Biozones VIII, VII, and VI at around 27-17 cal kyr BP with planktonic foraminiferal maximum and benthic foraminiferal minimum are found in a dark layer of TL-2, which was formed during the period of the lowest sea level in the LGM. Biozone IV, 12-11 cal kyr BP, is characterized by low oxygen tolerant benthic species of Bolivina pacifica, and correlates with dark layer TL-1, which implies that the deep circulation of Japan Sea was severely reduced for a short period during (or soon after) the Younger Dryas Cooling Event. B III represents the planktonic foraminiferal minimum zone, which marks the transition from cool water species to warm water species in planktonic foraminifera. Foraminiferal stratigraphy reveals that the sedimentation rate of the Umitaka spur sediments varied significantly depending on topography such as pockmarks or mounds.
{"title":"Lithofacies and Foraminiferal Stratigraphy for the Last 32000 Years in the Methane Seep Area of Umitaka Spur, off Joetsu","authors":"H. Nakagawa, Maki Suzuki, E. Takeuchi, R. Matsumoto","doi":"10.5026/JGEOGRAPHY.118.969","DOIUrl":"https://doi.org/10.5026/JGEOGRAPHY.118.969","url":null,"abstract":"Plantonic and benthic foraminifera are analyzed with 11 sediment cores recovered from the Umitaka Spur area of the Joetsu Basin off Joetsu, Niigata Prefecture. The area is characterized by active methane seeps and methane hydrates. We recognize 12 foraminiferal biozones (Biozone I to XII in descending order) in the last 32000 years based on three selected cores (two well-dated and one longest), and apply them to another 8 cores for correlation. Sediment cores are divided into five lithologic units as massive to bioturbated mud (lithologic unit 1), thinly laminated mud (unit 2), gray massive mud (unit 3), thinly laminated dark mud (unit 4), and bioturbated mud (unit 5) from upper to lower. Lithologic units 2 and 4 correspond to basin-wide thinly laminated layers, previously reported as TL-1 and TL-2, respectively. The Japan Sea became a closed inland basin during the lowest sea level period of the last glacial maximum (LGM) at 27-26cal kyr BP (Biozone VIII). The surface water reached the lowest salinity level, while the bottom water was strongly anoxic due to reduced vertical circulation. An expulsion of a large amount of methane occurred on the Umitaka Spur during the LGM due to a massive dissociation of subsurface methane hydrate. Biozones VIII, VII, and VI at around 27-17 cal kyr BP with planktonic foraminiferal maximum and benthic foraminiferal minimum are found in a dark layer of TL-2, which was formed during the period of the lowest sea level in the LGM. Biozone IV, 12-11 cal kyr BP, is characterized by low oxygen tolerant benthic species of Bolivina pacifica, and correlates with dark layer TL-1, which implies that the deep circulation of Japan Sea was severely reduced for a short period during (or soon after) the Younger Dryas Cooling Event. B III represents the planktonic foraminiferal minimum zone, which marks the transition from cool water species to warm water species in planktonic foraminifera. Foraminiferal stratigraphy reveals that the sedimentation rate of the Umitaka spur sediments varied significantly depending on topography such as pockmarks or mounds.","PeriodicalId":356213,"journal":{"name":"Chigaku Zasshi (jounal of Geography)","volume":"4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132744158","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2009-02-25DOI: 10.5026/JGEOGRAPHY.118.128
成騎 荻原, 理 石崎, 良 松本
The Umitaka spur and the Joetsu knoll in the eastern margin of the Japan Sea off Naoetsu are characterized by a high methane flux accompanied by the formation of methane hydrates. Several sediment cores were obtained from this region during the “Natsushima” NT-06-19 cruise. Various geochemistry analyses were carried out on these samples. ANME-1 and ANME-2 groups of archaea were distinguished by biomarkers. ANME-1 was found from the sediment sample covered by a bacterial mat with the maximum concentration of dissolved methane in pore water. The samples in which ANME was detected are characterized by a remarkably high sulphur content.
{"title":"なつしまNT-06-19航海（直江津沖海鷹海脚および上越海丘）によって採取された堆積物柱状試料の有機地球化学分析","authors":"成騎 荻原, 理 石崎, 良 松本","doi":"10.5026/JGEOGRAPHY.118.128","DOIUrl":"https://doi.org/10.5026/JGEOGRAPHY.118.128","url":null,"abstract":"The Umitaka spur and the Joetsu knoll in the eastern margin of the Japan Sea off Naoetsu are characterized by a high methane flux accompanied by the formation of methane hydrates. Several sediment cores were obtained from this region during the “Natsushima” NT-06-19 cruise. Various geochemistry analyses were carried out on these samples. ANME-1 and ANME-2 groups of archaea were distinguished by biomarkers. ANME-1 was found from the sediment sample covered by a bacterial mat with the maximum concentration of dissolved methane in pore water. The samples in which ANME was detected are characterized by a remarkably high sulphur content.","PeriodicalId":356213,"journal":{"name":"Chigaku Zasshi (jounal of Geography)","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-02-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122620074","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2009-02-25DOI: 10.5026/JGEOGRAPHY.118.72
正人 上嶋, 清和 西村, 清行 岸本, 峰男 弘松, 幹夫 佐藤, 良 松本
A remarkable reflection record of a deeper part (> 200 m) appeared on the fish finder. Gas bubbling was confirmed directly by the ROV (Hyper-Dolphin/Natsushima) diving off Joetsu in the eastern part of the Sea of Japan. Visualization, using geographical feature mapping and side-scan sonar images of the topography, was useful for investigating methane hydrate and associated carbonates at the sea bottom. Besides, a sub-bottom profiling study produced useful information for detecting buried methane hydrate and carbonates, because some of them had been identified previously by piston core sampling studies. DAI-PACK (Deep sea Acoustic Imaging Package) was set on the ROV (Hyper-Dolphin) and the survey extended to a length of approximately 20 km and covered a total area of 900,000. A detailed distribution of patch-shaped rough geographical features, some fault-like lineaments and sub-bottom profile records (about a maximum of 15 m deep), were obtained by five dives during the NT07-20 and the NT08-09 cruises. The round-shaped patches of rough geographical features are thought to have been formed by gas supplied to the surface through fault systems.
{"title":"上越沖, 海底表層メタンハイドレート賦存域での深海底構造・微地形調査について","authors":"正人 上嶋, 清和 西村, 清行 岸本, 峰男 弘松, 幹夫 佐藤, 良 松本","doi":"10.5026/JGEOGRAPHY.118.72","DOIUrl":"https://doi.org/10.5026/JGEOGRAPHY.118.72","url":null,"abstract":"A remarkable reflection record of a deeper part (> 200 m) appeared on the fish finder. Gas bubbling was confirmed directly by the ROV (Hyper-Dolphin/Natsushima) diving off Joetsu in the eastern part of the Sea of Japan. Visualization, using geographical feature mapping and side-scan sonar images of the topography, was useful for investigating methane hydrate and associated carbonates at the sea bottom. Besides, a sub-bottom profiling study produced useful information for detecting buried methane hydrate and carbonates, because some of them had been identified previously by piston core sampling studies. DAI-PACK (Deep sea Acoustic Imaging Package) was set on the ROV (Hyper-Dolphin) and the survey extended to a length of approximately 20 km and covered a total area of 900,000. A detailed distribution of patch-shaped rough geographical features, some fault-like lineaments and sub-bottom profile records (about a maximum of 15 m deep), were obtained by five dives during the NT07-20 and the NT08-09 cruises. The round-shaped patches of rough geographical features are thought to have been formed by gas supplied to the surface through fault systems.","PeriodicalId":356213,"journal":{"name":"Chigaku Zasshi (jounal of Geography)","volume":"35 2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2009-02-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125820187","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2008-12-25DOI: 10.5026/jgeography.117.1029
Hirohiko Kashiwagi, Y. Ogawa, N. Shikazono
The global carbon cycle controls the climate change in the Earth's environment on a geological timescale and is mainly associated with greenhouse effects produced by atmospheric carbon dioxide (CO2) and methane (CH4). This paper reviews the relationship between the global carbon cycle and presumed climate events during the Cenozoic. The global carbon cycle is primarily regulated by the balance between weathering and metamorphism-volcanism. Moreover, the organic carbon subcycle involving oxidative weathering and burial is of secondary importance. The balance of these geochemical processes results in variations of atmospheric CO2. The past climate on a geological time scale is reconstructed by several geochemical and paleontological methods or proxies. For example, sea-surface and deep-water temperature are deduced from oxygen isotope ratio and Mg/Ca ratio of foraminiferal tests. Terrestrial atmospheric temperature is estimated from leaf fossil and paleovegetation. Atmospheric CO2 level is calculated from carbon isotope ratios of phytoplankton and soil carbonate, stomatal density of leaf fossil, boron isotope ratio of foraminiferal test, Ce anomaly, and global carbon cycle modeling. It is important to consider their advantages and disadvantages in order to evaluate the paleoclimate adequately. Next, we discuss climate change based on these proxies. As a general trend, the Cenozoic climate change is characterized by a transition from ice-free to ice-covered conditions across the Eocene/Oligocene boundary. The Earth's surface environment was significantly warmed from the Paleocene to the Eocene by high levels of atmospheric CO2. Thereafter, it gradually cooled towards the present, which is possibly attributed to changes in ocean currents and other marine environments accompanying continental drift. This trend has been punctuated by several short-term climate events. The Paleocene-Eocene Thermal Maximum (PETM) was a remarkable warming event at the Paleocene/Eocene boundary, possibly attributed to the release of methane from hydrates into the atmosphere. Rapid cooling occurred at the Eocene/Oligocene boundary to form extensive continental ice sheets including the Antarctica, which seems to have been caused by atmospheric CO2 and change of oceanographic circulation and marine environment. After a moderate period from the late Oligocene to the early Miocene, there was a transient but significant warming in the middle Miocene. Since then, the Earth's environment has gradually cooled towards the present accompanied by the evolution of glaciations and marine environmental changes but a causal link between cooling and global carbon cycle has recently been pointed out. Although the carbon cycle including atmospheric CO2 and CH4 cannot explain all of the global climate changes in Cenozoic, it has undoubtedly played a dominant role on the Earth's climate.
{"title":"The Global Climate Change over the Cenozoic Considered from the Carbon Cycle","authors":"Hirohiko Kashiwagi, Y. Ogawa, N. Shikazono","doi":"10.5026/jgeography.117.1029","DOIUrl":"https://doi.org/10.5026/jgeography.117.1029","url":null,"abstract":"The global carbon cycle controls the climate change in the Earth's environment on a geological timescale and is mainly associated with greenhouse effects produced by atmospheric carbon dioxide (CO2) and methane (CH4). This paper reviews the relationship between the global carbon cycle and presumed climate events during the Cenozoic. The global carbon cycle is primarily regulated by the balance between weathering and metamorphism-volcanism. Moreover, the organic carbon subcycle involving oxidative weathering and burial is of secondary importance. The balance of these geochemical processes results in variations of atmospheric CO2. The past climate on a geological time scale is reconstructed by several geochemical and paleontological methods or proxies. For example, sea-surface and deep-water temperature are deduced from oxygen isotope ratio and Mg/Ca ratio of foraminiferal tests. Terrestrial atmospheric temperature is estimated from leaf fossil and paleovegetation. Atmospheric CO2 level is calculated from carbon isotope ratios of phytoplankton and soil carbonate, stomatal density of leaf fossil, boron isotope ratio of foraminiferal test, Ce anomaly, and global carbon cycle modeling. It is important to consider their advantages and disadvantages in order to evaluate the paleoclimate adequately. Next, we discuss climate change based on these proxies. As a general trend, the Cenozoic climate change is characterized by a transition from ice-free to ice-covered conditions across the Eocene/Oligocene boundary. The Earth's surface environment was significantly warmed from the Paleocene to the Eocene by high levels of atmospheric CO2. Thereafter, it gradually cooled towards the present, which is possibly attributed to changes in ocean currents and other marine environments accompanying continental drift. This trend has been punctuated by several short-term climate events. The Paleocene-Eocene Thermal Maximum (PETM) was a remarkable warming event at the Paleocene/Eocene boundary, possibly attributed to the release of methane from hydrates into the atmosphere. Rapid cooling occurred at the Eocene/Oligocene boundary to form extensive continental ice sheets including the Antarctica, which seems to have been caused by atmospheric CO2 and change of oceanographic circulation and marine environment. After a moderate period from the late Oligocene to the early Miocene, there was a transient but significant warming in the middle Miocene. Since then, the Earth's environment has gradually cooled towards the present accompanied by the evolution of glaciations and marine environmental changes but a causal link between cooling and global carbon cycle has recently been pointed out. Although the carbon cycle including atmospheric CO2 and CH4 cannot explain all of the global climate changes in Cenozoic, it has undoubtedly played a dominant role on the Earth's climate.","PeriodicalId":356213,"journal":{"name":"Chigaku Zasshi (jounal of Geography)","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-12-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129460396","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2008-12-25DOI: 10.5026/JGEOGRAPHY.117.997
忠徳 後藤, 均 三ケ田
Electromagnetic (EM) methods have been developed for estimating the apparent resistivity or conductivity of material composing subsurface structure depending on survey objectives, while seismic methods are applied mainly to understand geological structure or stratigraphy. Magnetotelluric subsurface sounding (MT) methods are proven tools detect high-conductivity anomalies in the Earth's interior; controlled source EM (CSEM) methods detect high-conductivity anomalies; and, nuclear magnetic resonance (NMR) methods estimate “the mean free path” of hydrogen atoms in various molecules composing underground materials. Regarding methodologies, EM methods frequently applied in practice are: (1) natural source MT methods, (2) artificial source MT or EM methods, and (3) borehole EM methods. The fundamental principles of these methods can be summarized as measuring the induction effects of a survey target using a natural or artificial electromagnetic source. Finally, we investigate examples of recent EM approaches in connection with seismic methods and discuss the integration of survey data from both methods as a key to exploring underground structures not only in terms of stratigraphic interpretation but also for estimating material physical properties.
{"title":"電磁気法探査（EM法探査）技術の現状と展望","authors":"忠徳 後藤, 均 三ケ田","doi":"10.5026/JGEOGRAPHY.117.997","DOIUrl":"https://doi.org/10.5026/JGEOGRAPHY.117.997","url":null,"abstract":"Electromagnetic (EM) methods have been developed for estimating the apparent resistivity or conductivity of material composing subsurface structure depending on survey objectives, while seismic methods are applied mainly to understand geological structure or stratigraphy. Magnetotelluric subsurface sounding (MT) methods are proven tools detect high-conductivity anomalies in the Earth's interior; controlled source EM (CSEM) methods detect high-conductivity anomalies; and, nuclear magnetic resonance (NMR) methods estimate “the mean free path” of hydrogen atoms in various molecules composing underground materials. Regarding methodologies, EM methods frequently applied in practice are: (1) natural source MT methods, (2) artificial source MT or EM methods, and (3) borehole EM methods. The fundamental principles of these methods can be summarized as measuring the induction effects of a survey target using a natural or artificial electromagnetic source. Finally, we investigate examples of recent EM approaches in connection with seismic methods and discuss the integration of survey data from both methods as a key to exploring underground structures not only in terms of stratigraphic interpretation but also for estimating material physical properties.","PeriodicalId":356213,"journal":{"name":"Chigaku Zasshi (jounal of Geography)","volume":"2014 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2008-12-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127421206","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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