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| index | Vol. 51 | 1 | 2/3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | Japanese Index | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
A new groundwater observation well constructed on the Suzuka-toen fault zone - the Hokusei well
Tsutomu SATO(Earthquake Research Department, GSJ), Makoto TAKAHASHI(Earthquake Research Department, GSJ), Eikichi TSUKUDA(Earthquake Research Department, GSJ), Hisashi UEMURA(Nittetsu Mining Consultants Co., Ltd.) and Toyomatsu SUGAWARA(Nittetsu Mining Consultants Co., Ltd.)
2000
vol. 51 (1) P. 1-16
8 figs., 5 tables
Keywords: groundwater, Hokusei, Fumotomura fault, Suzuka-toen fault zone, Earthquake prediction
Abstract: A new observation well, the Hokusei well, was constructed on the Suzuka-toen fault zone for earthquake prediction and monitoring the activity of faults. As for the geology at the Hokusei well, a syncline of the Quaternary formation is reported in addition to an active fault, the Fumotomura fault. To monitor two kinds of groundwater contained in such geologic structures, syncline and active fault, the Hokusei well have double casing pipes that are arranged concentrically. The depth of the wells are 290 m and 500 m of the outer and inner pipes, respectively. In the inner pipe, there is a sequence of the screen near the axis of the syncline. In the outer pipe, there are three sequences of the screens near the Fumotomura fault. The depth of the Fumotomura fault at the point of the well is assumed to be 170 - 190 m based on the core sample observation. The groundwater obtained from the fault depth is characterized to be rich in Si and Fe. The transmissivities of all aquifers are estimated to be about 10-6 m2/s by pumping tests.
Late Cenozoic ore deposits and their sulfur isotopic ratios of the northeastern Hokkaido, Japan
Shunso ISHIHARA(Geological Survey of Japan), Masahiro YAHATA(Geological Survey of Hokkaido), Yukitoshi URASHIMA and Yasushi WATANABE(Geological Survey of Japan)
2000
vol. 51 (1) P. 17-28
4 figs., 3 tables
Keywords: Late Cenozoic, Kitami province, volcanogenic, base metal deposit, gold-silver deposit, mercury deposit, 34S value, ilmenite series, magnetite series
Abstract: Sulfur isotopic ratio (34S) was determined on sulfide minerals and ores from base metal deposits (23 samples), gold-silver deposits (29 samples) and mercury deposits (9 samples), and a large number of negative 34S values were discovered. Together with the previously reported data, the base metal deposits have two groups of 34S values: -12.9 to -9.8 and -2.7 to +6.2 permil. The first group is considered genetically related to ilmenite-series granitoids, which have -6.3 permil on an average 34S value of the rock sulfur. The second group is essentially formed with magnetite-series volcanic and subvolcanic activities (Motokura-Jotoku), but locally contaminated with sedimentary sulfur from the wall rocks (Kitami). Gold-silver deposits have a wide range of -9.0 to +9.0 permil34S. The values are especially low (-9.0 `-0.7) in those of the Omu-Sanru graben and the northernmost part of the Monbetsu-Kamishihoro graben, where important ore deposits of Konomai, Hokuryu, Numano-ue and Sanru are distributed. These negative 34S values may indicate the existence of reduced-series volcanic rocks in these regions. A regional N-S variation in the 34S values of the gold-silver deposits seen in the northeastern Hokkaido is considered to reflect essentially the regional difference in the ilmenite/magnetite-series volcanic activities. Mercury deposits have the most negative values (-14.2 to +0.4 ) among the three commodity groups, and could also be related to ilmenite-series volcanism.
Recent surface faulting of the North Anatolian fault along the 1943 Ladik earthquake ruptures
Toshikazu YOSHIOKA(Earthquake Research Department, GSJ), Koji OKUMURA(Hiroshima University), Ismail KUSCU(General Directorate of Mineral Research and Exploration of Turkey) and Omer EMRE(General Directorate of Mineral Research and Exploration of Turkey)
2000
vol. 51 (1) P. 29-35
6 figs., 1 table
Keywords: North Anatolian fault, Turkey, active fault, paleoseismology, trench, Ladik earthquake
Abstract: We excavated the North Anatolian fault on the surface rupture of the 1943 Ladik earthquake in order to specify the recent faulting history of the segment. A trench was opened across the fault on an alluvial fan surface northwest of Havza. The sediments exposed on the trench walls consist of massive pebbly silt and gravel bearing pottery fragments of the Roman period. A few fault strands cut through these sediments. One strand of the faults cuts the sediments up to just below the ground surface. This strand was presumed to be formed during the last event of 1943. We recognized at least three faulting events including the 1943 event. The radiocarbon ages of charcoal pieces and animal bones indicate that the penultimate event was likely to have occurred after the 11th century and before the 14th century. The estimated interval of 600 to 900 year recurrence time is much longer than the estimates from trench studies on the North Anatolian fault in Gerede and Erzincan are 280 km west and 380 km east of this site, respectively.
Refined magnetostratigraphy of the Early Miocene sequence in the Yatsuo area, central Japan
Yasuto ITOH(Osaka Prefecture University) and Mahito WATANABE(Mineral and Fuel Resources Department, GSJ)
2000
vol. 51 (1) P. 37-45
7 figs., 2 tables
Keywords: Yatsuo, Toyama, Japan, magnetostratigraphy, Miocene, Neogene
Abstract: We have refined magnetostratigraphy of the Early Miocene sequence in the Yatsuo area, central Japan. On the basis of progressive alternating field and thermal demagnetization tests for samples from the Iwaine, Iozen and Kurosedani Formations, primary remanent magnetization of the normal polarity was suggested for the Iwaine Formation although correction for tectonic tilting is not applicable. On the other hand, stable remanent magnetization of samples from the Iozen and Kurosedani Formations show the reversed polarity. Untilted characteristic directions of the Kurosedani Formation do not have significant deflection in magnetic declinations, which is concordant with previous studies. Together with biostratigraphic and chronological framework, the present result indicates that the Iwaine / lower Iozen Formations and upper Iozen / Kurosedani Formations are assigned to the Chron C5Cn and C5Br of the standard geomagnetic polarity time-scale, respectively.
