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Matsukawa M.,Tokyo Gakugei University | Obata I.,Fukada Geological Institute
Cretaceous Research | Year: 2015

The Lower Cretaceous ammonite fauna of Japan was influenced by the Tethyan, Boreal and North Pacific realms with their oceanic current patterns and ammonite distributions. The hypothesis of oceanic circulation can be utilized to interpret the existence of the "Bering Strait" and the changing position of the "Boreal front," that is the contact region of warm and cold-water masses. To understand such a system fully, a comprehensive understanding of the geographical distribution of ammonite faunas is required. The occurrence of twenty-five ammonite species, belonging to twenty genera, is confirmed in the Barremian to Albian of Japan. Of these, 24 species are described in this paper, including Barremites macroumbilicus sp. nov. The fauna can be divided into three associations, lower, middle, and upper, indicating late Barremian, late Aptian, and late Albian of the European standard zonation. The faunal characters suggest that the habitats of these ammonite faunas may have changed during later Early Cretaceous, with faunas characterizing three different environments, i.e., nearshore, intermediate, and distal shelf to upper slope setting. Ammonites of the lower association (late Barremian) are related to those of the Tethys, Boreal European, and circum-Pacific regions, and suggest that the Early Cretaceous Katsuuragawa Basin was deposited under the influence of currents from both high latitude and equatorial areas. The occurrence of Crioceratites (Paracrioceras) suggests that the Boreal European elements, including Simbirskites and Crioceratites (Paracrioceras), transited between Northwest Europe and Japan through the Arctic Sea, indicating that the Pacific Ocean was connected with the Arctic Sea at that time. The second association (late Aptian) is composed of ammonites of the Tethyan and circum-Pacific regions. As European Boreal ammonite taxa are absent in this association, it is concluded that the Pacific Ocean probably was not connected with the Arctic Sea at the time. Consequently, the "Boreal Front," marking the contact between warm and cold water masses, was located at mid-latitude in the "Bering Strait" region during Barremian and subsequently moved northward during Albian. The uppermost ammonite association (late Albian) also consists of Tethyan and circum-Pacific taxa. Desmoceras (Pseudouhligella) poronaicum expanded its range with northward and eastward circulation of oceanic currents, suggesting the current must have represented a warm water-mass from the equator. The species subsequently migrated from the southern Katsuuragawa Basin to the Hokkaido area during late to latest Albian. © 2014 Elsevier Ltd.

Kawamura K.,Fukada Geological Institute | Kawamura K.,Japan Agency for Marine - Earth Science and Technology | Sasaki T.,University of Tokyo | Sasaki T.,Ocean Engineering and Development Co. | And 3 more authors.
Geophysical Research Letters | Year: 2012

We describe in detail possible large submarine landslides, several tens of kilometers in length and width, on the trench landward slope of the Japan Trench on the basis of high-resolution topographic surveys and detailed seafloor observations. These slides stopped at the toe of the trench slope. After initial movement of the toe along a basal decollement or thrust of the trench landward slope wedge during an earthquake, the basal frictional condition(s) might change drastically from static to dynamic, thus reducing the frictional strength. As a result, rapid submarine landsliding push downward on the toe, generating large horizontal displacements for tsunamis. This hypothesis should explain suitably the relation between large displacement of the thrust fault and tsunami generation by the 2011 Tohoku earthquake as well as tsunami generation by the 1896 Tohoku earthquake. Copyright 2012 by the American Geophysical Union.

Haraguchi S.,University of Tokyo | Ishii T.,Fukada Geological Institute | Kimura J.-I.,Japan Agency for Marine - Earth Science and Technology | Kato Y.,University of Tokyo
Contributions to Mineralogy and Petrology | Year: 2012

The northern Kyushu-Palau Ridge (KPR), remnant conjugate arc of the Izu-Ogasawara (Bonin)-Mariana (IBM) active arc, is dominated by basalt-andesite except for the Komahashi-Daini Seamount where acidic plutonic rocks of 38 Ma were recovered. These mafic to intermediate volcanics are produced by the rifting volcanism in the proto-IBM arc associated with spreading of the Shikoku Basin. The HFSE and HREE contents and ratios of these volcanics indicate enriched source mantle composition compared to recent volcanic front. The LILE ratios exhibit similar characteristics to reararc volcanism of the recent Izu arc, and some enriched volcanics exhibit high abundance of sediment melt inputs. Based on these observations and compilations of the published data set, the replacement event of the wedge mantle under the IBM arc occurred two times. The first event occurred between 45 and 38 Ma, with Pacific type mantle being replaced by depleted Indian type mantle. The second event occurred between 36 and 25 Ma, enriched mantle flowed from reararc side. The slab component during the proto-IBM arc rifting was a similar characteristic to recent reararc volcanism of the Izu arc, and sediment melt added in a local area. © 2011 Springer-Verlag.

Kitahashi T.,University of Tokyo | Kawamura K.,Fukada Geological Institute | Kawamura K.,Yamaguchi University | Kojima S.,University of Tokyo | Shimanaga M.,Kumamoto University
Deep-Sea Research Part I: Oceanographic Research Papers | Year: 2013

We investigated the genus diversity and community composition of harpacticoid copepods and their relationship with environmental factors around the Kuril Trench (490-7090. m). Harpacticoid densities did not decrease with water depth and were highest at 1000. m water depth. Diversity values based on the number of genera, Shannon diversity and the expected number of genera (rarefaction) indicated unimodal patterns with water depth, with peaks at intermediate depth; genus evenness increased with water depth and slightly decreased at hadal depths. This result suggested that the general relationship between water depth and diversity described for macrofauna and megafauna could be extended to meiofauna across all depth ranges. However, the regulating factor that affects harpacticoid diversity could not be identified. The community composition of harpacticoids gradually changed with water depth (from bathyal to hadal depths). In addition, comparison of assemblages between the trench slope, trench floor and abyssal plain suggested that the community found at hadal depth was largely different from those found on the trench slope and abyssal plain. Multivariate analyses suggested that water depth, or certain factors associated with water depth, affects harpacticoid assemblages around the Kuril Trench. © 2013 Elsevier Ltd.

Chigira M.,Kyoto University | Tsou C.-Y.,Kyoto University | Matsushi Y.,Kyoto University | Hiraishi N.,Fukada Geological Institute | And 2 more authors.
Geomorphology | Year: 2013

Typhoon Talas crossed the Japanese Islands between 2 and 5 September 2011, causing more than 70 deep-seated catastrophic landslides in a Jurassic to Paleogene-lower Miocene accretion complex. Detailed examination of the topographic features of 10 large landslides before the event, recorded on 1-m DEMs based on airborne laser scanner surveys, showed that all landslides had small scarps near their future crowns prior to the slide, and one landslide had linear depressions along its future crown as precursor topographic features. These scarps and linear depressions were caused by gravitational slope deformation that preceded the catastrophic failure. Although the scarps may have been enlarged by degradation, their sizes relative to the whole slopes suggest that minimal slope deformation had occurred in the period immediately before the catastrophic failure. The scarp ratio, defined as the ratio of length of a scarp to that of the whole slope both measured along the slope line, ranged from 5% to 21%. Careful examination of aerial photographs from another four large landslides, for which no high-resolution DEMs were available, suggested that they also developed scarps at their heads beforehand. Twelve of the 14 landslides we surveyed in the field had sliding surfaces with wedge-shaped discontinuities that consisted of faults and bedding, suggesting that the buildup of pore pressure occurs readily on wedge-shaped discontinuities in a gravitationally deformed rock body. Most of the faults were undulatory and were probably thrust faults that formed during accretion. Other types of gravitational deformation were also active; e.g., flexural toppling and buckling were observed to have preceded one landslide. © 2013 Elsevier B.V.

Kamemura K.,Fukada Geological Institute
ISRM International Symposium - 8th Asian Rock Mechanics Symposium, ARMS 2014 | Year: 2014

In Japan, a lot of underground structures have been constructed in spite of complex and poor geological conditions and are now in use. On the other hand, an aseismic design to prevent the severe accident of structures is very important in Japan. Though, an aseismic design of structures constructed in rock has not been well discussed up to now. This is because we have had a tacit understanding that a seismic vibration is small enough in the deep underground and underground structures do not respond like structures which have been constructed on the ground surface. However, in the recent earthquakes which had caused a lot of structural damage, some cases where tunnel structures had been damaged had been also reported. So, the aseismic design for the structures constructed in rock mass should be discussed as an important and urgent problem, especially for the new structures which are going to utilise various properties of rock mass. They are high-level radio-active waste disposal facility, and underground storage facility for oil and gas. If these underground facilities are damaged and lose their functions by great earthquake, a social influence is too serious. In this paper, the present situation of static and aseismic design for underground structures ranging from cut-and-cover tunnel in a shallow ground to mountain tunnel in the deep rock mass is reviewed. And problems that should be discussed to establish a proper method of aseismic design are presented. © 2014 by Japanese Committee for Rock Mechanics.

Kamemura K.,Fukada Geological Institute
46th US Rock Mechanics / Geomechanics Symposium 2012 | Year: 2012

In the design of rock structures such as tunnels and underground caverns, a continuity analysis considering the nonlinearity of rock has been used in many cases. On the other hand, the mechanical and hydraulic behavior of hard rock is governed by discontinuities of various sizes and numbers contained in rock mass. Therefore, the EDZ (excavation disturbed zone) assumed based on the result of the continuity analysis may differ from that of obtained by the analysis considering discontinuities explicitly. This means that the performance evaluation result of rock structures may change by evaluating discontinuity explicitly or not. In the performance evaluation of the high-level radioactive-wastes disposal facility and of the water-sealing type underground storage facility for gas and oil, it is necessary to examine a stress-fluid coupled behavior, because the requested performance to these facilities is greatly depending on the quality of sealing and water-tightness. In such examination, not only a mechanical stability but also a hydraulic performance such as extremely low permeability for long period is examined in detail. Here, the techniques concerning to stress-fluid coupling analysis which has been adopted up to now is reviewed and problems in the performance evaluation to important and highly reliable rock structures are examined. Copyright 2012 ARMA, American Rock Mechanics Association.

Progressive change of microfabrics of deep-sea sediments during early diagenesis was analyzed using two drill cores collected from the Sites U1305 and U1306 of the Integrated Ocean Drilling Program Expedition 303 in the Labrador Sea in the northwest Atlantic Ocean. Microfabrics were analyzed by scanning electron microscope and deduced from anisotropy of magnetic susceptibility. Different microfabrics in three layers were distinguished in both cores: Surface layer with general void ratio >2.5, subjacent layer with void ratio 2.5-1.5, and deep layer with void ratio <1.5. Microfabrics of the sediments change downward (toward deeper part), as well as magnetic susceptibility anisotropy. Microfabrics in the surface layer are non-directional and characterized by the presence of many macropores larger than 10 μm in diameter. Clay platelets in this layer are linked to each other with edge-to-edge or high-angle edge-toface (EF) contact. In the underlying layer, contact relations of clay platelets change to low angle EF type. Coarse siliciclastic fractions of this layer show horizontal preferred orientation, most probably due to overloading of the surface layer. Sizes of macropores decrease to several mm in diameter. In the lowest layer, clay platelets take horizontal preferred orientation according to further burial consolidation. Thus, the microfabrics of the sediments are developed from non-directional to preferred horizontal orientation with burial consolidation by following processes; 1) rotation of coarse grains in the layer with the void ratio>2.5 and 2) change of clay microfabrics in the layer with the void ratio <2.5.

Kawamura K.,Fukada Geological Institute
Geomechanics and Geotechnics: From Micro to Macro - Proceedings of the International Symposium on Geomechanics and Geotechnics: From Micro to Macro, IS-Shanghai 2010 | Year: 2011

Detailed three dimensional microfabric images of deep-sea sediments were revealed from Anisotropy of Magnetic Susceptibility (AMS) measurements, Scanning Electron Microscope (SEM) observations and micro X-ray CT analyses. Studied specimens of -300 meter composite depth (mcd) were collected from Sites U1302, 04, 05, 06, 07, and 08, in the North Atlantic during the Integrated Ocean Drilling Program (IODP) Expedition 303. The sediments from Sites U1302, 05, 06 and 07 were mainly composed of silty clay, those from Sites U1304 and 08 were composed of mainly pelagic sediments. The microfabric observation indicates that the sedimentary particles of silty clay re-arrange gradually from non-directional orientation to preferred horizontally orientation due to burial consolidation. In contrast, the sedimentary particles of pelagic sediments does not re-arrange well throughout the cores. The AMS and X-ray CT results are supported by detailed microfabric observations. Thus, the silty clay from the North Atlantic develops gradually into a shaly structure during burial, whereas similar fabrics in the pelagic sediments are not well developed. © 2011 Taylor & Francis Group.

Takahashi T.,Fukada Geological Institute | Tanaka S.,Fukada Geological Institute
Exploration Geophysics | Year: 2013

Estimating the strength, especially compressive strength, of rocks is one of the major problems in many civil engineering applications. Compressive strength of a rock is usually measured in a laboratory test of rock specimens obtained in boreholes drilled in the investigation site. If seismic velocity can be used for estimating rock strength, the seismic method can be employed effectively for profiling strength of a large rock mass because it is capable of determining subsurface seismic properties over a large area. Rock strength is often estimated from seismic velocity using correlations between data of each property, measured in the specific rock mass, or by using existing empirical relations. These techniques, however, have problems in accuracy and reliability of their estimates, because the correlations between measured data generally are made with a small number of data, and empirical relations are restricted for applicable rock types. In this study, a rock physics model is studied to estimate the compressive strength from seismic velocity more accurately and reliably. The confined compressive strength-seismic velocity relationship is modelled by combining two effective-medium models for (1) the confined compressive strength v. porosity and (2) seismic velocity v. porosity. The model is applied to S-wave velocity log data in soft sedimentary rocks, and the model predictions are compared with confined compressive strength, measured with the triaxial compression test on rock cores sampled in the same borehole as that used for the velocity logging. The model is also applied to ultrasonic P-wave velocity and confined compressive strength data measured in the laboratory, using core samples of sedimentary rocks collected from various sites in Japan. Good agreement between model-calculated and measured data in the confined compressive strength-seismic velocity relationships in these cases reveals that the confined compressive strength can be estimated from seismic velocity using a rock physics model. © 2013 ASEG.

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