アゾレス諸島は，ヨーロッパ大陸から1600km離れた北大西洋にある火山諸島（37°～40°N，25°～31°W）で，9つの島からなる．15世紀に移民が始まって以来，約30の噴火が記録されている．テルセイラ島はこのうち3番目に大きな島（402km2）で，島内にはカルデラ火山，溶岩ドーム，砕屑丘などがある． Algar do Carvãoはテルセイラ島中央部のスコリア丘にある溶岩洞窟である．この洞窟は火山の火道に相当する部分で，地上の穴の直径は地表部分で約20m，深さは約90mである．観光客はトンネルを通って深さ30mの位置（写真下部の人のいる場所）からこの溶岩洞窟に入る．階段を下りていくと，内部はいくつもの大きな部屋がつながっており，最下部には池がある．観光客は，まるで地底探検をしている気分を味わえる． （解説・写真：白尾元理）
We reconstruct the evolution of the active fault zone at Yokote Basin in northeast Japan based on new fission-track ages. The active fault zone consists of Obonai, Shiraiwa, and Senya faults. Fission-track dating was carried out from the late Pliocene to Pleistocene strata, developing along the active fault zone consisting of these faults. The number of samples was five. (1) Fission-track age of 1.5 ± 0.1 Ma (OB-03) was obtained from welded tuff in the Tazawa Formation around the Obonai fault. (2) Fission-track age of 1.85 ± 0.13 Ma (YG-01) was obtained from tuff in the Tazawa Formation around the south of the Obonai fault. (3) Fission-track age of 1.6 ± 0.3 Ma (FT-01) was obtained from the Kurisawa Formation around the Shiraiwa fault. (4, 5) Fission-track ages of 0.93 ± 0.14 Ma (FT-02) and 2.7 ± 0.4 Ma (FT-03) were obtained from tuffs in the Senya Formation around the Senya fault. YG-01 and FT-03 are likely to be young because of the possibility of reworked zircon crystals. As a result of making balanced and restored cross-sections across the active fault zone, the western boundary fault of the Mahiru mountains moves in the active fault zone after the frontal fault movements. Obonai and Shiraiwa faults were moved by the western boundary fault of the Mahiru mountains when the Senya fault began movement of the frontal fault.
We review seismic interferometry with an example of a numerical simulation. A cross-correlation of two seismic records at different receivers yields a virtual source record that corresponds to the seismic response observed at one receiver due to the source at another receiver location. By changing the combination of cross-correlations, as many virtual source records as the number of receivers used in an observation can be generated. Synthesized virtual source records have useful information for subsurface imaging or characterization of the Earth. Using this technique, we can use background seismic noise as a signal, and we can investigate the subsurface with controlled sources and an ingenious deployment of receivers adapted to the environment of a target field. By optimizing of data acquisition and processing method for the virtual source record, seismic interferometry can be widely applied to interesting problems in the Earth science.
The Daisekkei Valley (1600-2300 m ASL) is a late Pleistocene glaciated trough in the northern Japanese Alps, and its attractive landscape has enchanted many climbers. Even today, there is a late-lying snowpatch 2 km long at the bottom of the valley in midsummer. Unique natural conditions in and around the Daisekkei Valley (e.g., Quaternary rapid uplift, complex geology, humid climates, sparse vegetation cover) have been responsible for the occurrence of various geomorphic changes that threaten climbers. This study, using an image data-logger capable of capturing a JPG image with a fixed time-interval in the summer of 2007 reveals supranival debris movements, micro-weather conditions and the behavior of climbers in the Daisekkei Valley. Analysis of captured images indicates that the daily numbers of dangerous supranival debris movements gradually decreased from early June to early August and supranival debris movements were caused by rock fragments moving in from valley walls or tributaries to the snowpatch, as well as posture changes of rock fragments on the snow surface with rapid ablation. Besides, image-inspection allows us to consider the relationships among climber traffic, micro-weather, and holiday almanac. Using an image data-logger for monitoring geomorphic changes is considered to be effective for analyzing alpine environments.
Bulk organic carbon isotope (δ13Corg) analyses across the Cenomanian/Turonian boundary in Hokkaido, Japan, and high-resolution planktic foramiferal biostratigraphy indicate that the timing of the planktic foraminiferal disappearance in the northwestern Pacific was significantly earlier than that in the Atlantic region. δ13Corg shows a prominent ∼2‰ positive excursion, clear trough interval, steady plateau interval, and recovery interval, which can be used as very precise chemo-stratigraphic markers. Planktic foraminiferal biostratigraphy demonstrates a pair of diversity crisis at a horizon below the initial δ13Corg excursion and at the beginning of the plateau interval. This isolated double diversity crisis of planktic foraminifers has also been identified in the Western Interior region and northern Europe. The timings of this double diversity crisis in the Western Interior and Europe show quite good consistency on the basis of the δ13C chemo-stratigraphy. On the other hand, the double crisis in the northwestern Pacific is significantly earlier than those in the Western Interior and Europe. This offset indicates that expansion of the oxygen-depleted water mass in the northwestern Pacific preceded that in the Atlantic region.
The emplacement temperature of the AD915 Towada pyroclastic flow (To-a pyroclastic surge) is estimated from the emplacement temperature of crusts (pumices and a lithic fragment) within the surge deposits. The measured emplacement temperature of the pyroclastic surge varies vertically in the surge deposits. The lower part of the deposits shows low temperatures (300-500°C) because due to cooling by the cold ground surface. The middle part of the surge deposits, which was sandwiched by the lower and upper parts of the surge, shows high temperatures (350-680°C, mostly 620-650°C). The upper part of the surge deposits which was probably cooled by the atmosphere, shows moderate temperatures (less than 620°C, mostly 500-620°C).
A geomagnetic and topographic survey of the Main Crater Lake (MCL) on Volcano Island, Taal volcano, the Philippines, was conducted to identify the eruption mechanism of the volcano. A mound at the lake bottom was found near the northern part of MCL, which was not present at the 1986 survey. Called mound M, it was formed between 1986 and 2008 during a period of new fumarole activity, which started on the northeastern shore of MCL in the early 1990's. A geomagnetic survey found no Total Magnetic Field (TMF) anomaly corresponding to the mound, which implies that mound M is non-magnetic. The site coincides with the location of a high-temperature area detected by the ASTER satellite during the early 2005 volcanic crisis. The mound M might contain chemicals (chloride or sulphide?) deposited from volcanic gas. Two continuously-recording proton magnetometers were set up at two geothermal areas on Volcano Island. Recordings of TMF variations obtained over six months on Volcano Island showed excellent stability and precision for monitoring the volcanic activity.
We studied the morphogenetic movements associated with the formation of the Sekita Mountains and Iiyama Basin situated at the boundary between the Niigata and Nagano prefectures in central Japan. As a result, we obtained following conclusions. (1) The morphogenetic movement of the Sekita Mountains is a semicylindrical upwarping originating from faulting at both sides of the mountains. The origin was an inclined thrust of a basal block. In addition, it is assumed that the upheaval of the mountains due to a change in isostasy caused by erosion resulted in the four-thousand meter thick strata that constitutes the mountains, and erosion originated from a fold in the strata occurring in the middle Pleistocene. (2) The morphogenetic movement constituting the Iiyama Basin is a reverse fault, which originated from tilting and drawing of the basal crust as a result of a semicylindrical upwarping of the Kato Mountains situated at the east side of the Iiyama Basin. The upwarping was caused by magma ascending from a deep part of the crust. Therefore, the Iiyama Basin was formed as a fault-angle basin. The mountain body of Kenasi Volcano tilted toward the west through the process of forming the Iiyama Basin. We think the Iiyama Basin continued to subside at the rate of about one millimeter a year in the Holocene, based on radiocarbon dating of drilling core samples collected from sediments in the alluvial lowlands.
To better understand and update knowledge of the stratigraphy and foraminiferal and conodont faunal successions of Bashkirian-Moscovian (Pennsylvanian/Upper Carboniferous) boundary intervals in the Donets Basin of Ukraine, we studied the C21 to C26 suites (Limestones F to L) of the following eight stratigraphic sections located in the eastern part of the basin. These are the Karaguz, Volnukhino, Kriven'ky Yar, Rudnya, Zolotaya, and Malonikolaevka sections in Lugansk county and the Soroch'ya and Kholodnaya sections in Donetsk county. Among them, the Malonikolaevka section, which is located about 35km southwest of Lugansk and is documented for the first time in this study, provides important data on the faunal successions of the Bashkirian-Moscovian boundary interval, ranging from Limestones I2 to K3. Both the conodont and fusuline faunas record the appearances in the basal part of the C25 (K) Suite of several new taxa that are more characteristic of the early Moscovian. These forms include Declinognathodus donetzianus at the top of K1 in conodonts and Eofusulina triangula, E. trianguliformis, and a large Neostaffella species (N. vozhgalica) at K2 in fusulines. Thus, the K1-K2 interval is very promising as the potential position of the formal Bashkirian-Moscovian boundary in the Donets Basin. The data from the Malonikolaevka section, together with those from other sections in the present study, would be significant for future investigations of the Task Group to establish a GSSP close to the existing Bashkirian-Moscovian Boundary organized in IUGS Subcommission on Carboniferous Stratigraphy (SCCS).
The international symposium “Quaternary Environmental Changes and Humans in Asia and the Western Pacific” was held successfully in Tsukuba, Ibaraki Prefecture on November 19-22, 2007. The Japan Association for Quaternary Research jointly planned this symposium with National Institute of Advanced Industrial Science and Technology to commemorate the 50th anniversary of the establishment of the Japan Association for Quaternary Research and the 125th anniversary of the establishment of the Geological Survey of Japan. The purposes of the symposium were to communicate scientific results of Quaternary research in Japan to the rest of the world and promote international cooperation on Quaternary studies in the East Asian region. The symposium was held over three days and included four keynote lectures by leading international researchers, and 36 oral and 61 poster presentations during six sector sessions, which covered relationships between environmental change and human migration. One hundred and forty three participants, including 35 from foreign countries, discussed recent topics in Quaternary research. Moreover, agreement to hold a regular Quaternary International workshop in Asia (Asian Conference on Quaternary Research) was obtained as a result of discussions among representatives of Asian countries.
The seventh international symposium, “Cephalopods—Present and Past” was held at the International Conference Hall, Hokkaido University, Sapporo, Japan, during the period September 14-16, 2007; it was the first symposium to be held in Asia. This symposium was co-organized by the Organizing Committee of the symposium and the 21st Century Center of Excellence Program of the Faculty of Science, Hokkaido University, entitled “Neo-Science of Natural History” and was sponsored by the Palaeontological Society of Japan, the Malacological Society of Japan, and Mikasa City and Nakagawa Town, Hokkaido. A total of 97 experts on modern and fossil cephalopods from 14 countries attended the symposium, and 42 oral and 34 poster presentations were given during the seven sessions, viz. (1) Paleobiological aspects of fossil cephalopods, (2) Biological aspects of modern Coleoidea, (3) Cephalopod taphonomy and new techniques,(4) Paleobiology and systematics of Mesozoic Ammonoidea and Coleoidea, (5) Biostratigraphic and paleobiogeographic aspects of Ammonoidea, (6) New approaches to cephalopod biology and paleobiology, and (7) Paleoecology, biostratigraphy and extinction of Ammonoidea. In particular, interesting talks were given on the developmental biology and molecular systematics of living cephalopods and the comparative anatomy of exceptionally well-preserved fossil cephalopods with soft tissue remains. We sincerely appreciate the financial support provided by the Tokyo Geographical Society, which was used to invite key-note speakers from overseas.
The fifth conference of Cities on Volcanoes was held in Shimabara, Nagasaki, during the period November 19-23, 2007, under the sponsorship of the Shimabara City and the Volcanological Society of Japan. The conference, Cites on Volcanoes, is an international forum that has been organized every two years since 1998 by the Cities and Volcanoes Commission of IAVCEI, in which volcanologists and non-volcanologists, including city-planners, engineers, members of the mass media, and citizens discuss reducing risks from volcanic eruptions and related phenomena. Six hundred participants registered to attend the conference from 31 countries and regions. It was the first conference to be held in Asia. The main theme of the conference this time was “Coexisting with Volcanoes”, and the aim was sufficiently achieved with the supports of citizens, students, and volunteers from Shimabara City and its surrounding areas. Five hundred fifty-one papers were presented at ten sessions of three symposiums (knowing volcanoes, volcanoes and cities, and living with volcanoes). In addition to 10 scientific sessions, the organizing committee prepared several forums and outreach activities to which citizens, students, members of authorities and mass media could attend. In addition to registered participants, about 2,100 persons attended both scientific sessions and these forums. The statement of the conference was presented as the Heisei-shinzan appeal in the closing ceremony.
The present study represents an attempt to determine the sources of vermilion found in ancient Japanese burial mounds prior to the emergence of the ancient Yamato dynasty. For this purpose, cinnabar ores were collected from Chinese and Japanese mines, and samples of vermilion were also collected from ancient tombs. When the vermilion collected from the tombs was studied morphologically, different particle sizes were observed. However, the particle size of the artificial vermilion was found almost same. The metal contents of cinnabar ores were different for each Japanese mine: Niu (Mie Pref.), Yamato Mercury (Nara Pref.), Sui (Tokushima Pref.), and Itomuka (Hokkaido Pref.) mines. Arsenic (As) content was highest in cinnabar ore from Niu mine; Mn and Fe contents were highest in Yamato Mercury mine; and, the Ba, Ca, Co, Cr, and Sr contents were highest in Sui mine. When analyzing the metal contents of vermilion collected from ancient tombs in Nara Prefecture, vermilion collected from Kurozuka, Kamotsuba, and Tomio-Maruyama tombs showed a high As content, and vermilion from Tenjinyama tomb showed a high Mn content. Thus, the possibility was suggested of identifying the original vermilion mine from the metal contents. However, it is difficult to set borderlines for the metal contents of vermilion to identify the source mine. So, the ratios of sulfur isotope (δ34S) in ores and vermilion were compared. A high δ34S value of +22.6 ± 3.6‰ was found for the ore of Wanshan of Guizhou and from +6 to +10.6‰ for Xunyang of Shaanxi in China, as opposed to low values ranging from -7.3 ± 1.9 to -2.1 ± 1.6‰ for Japanese mines. It is thought that δ34S values are suitable for determining the sources of vermilion found in ancient tombs. In addition, high ratios from +7.4 to +22.8‰ were found in 1st- and 2nd-century burial sites in northern Kyushu and San'in, and lower ratios from -8.4 to -2.0‰ were found in burial sites of the 2nd through 6th centuries in central Japan. Therefore, powerful local chiefs living in northern Kyushu and San'in areas might have obtained vermilion through relations with China, but chiefs living in central Japan might have used vermilion collected from Japanese mines. In conclusion, the sources of vermilion collected in ancient tombs can be determined by measuring δ34S values. An additional analysis of a lead isotope ratio, for example, might also be necessary to determine the source of vermilion.