Geological prognosis ahead of a tunnel face     

Masahiro Hasegawa  Masaru Usui  Keinosuke Gotoh 《Engineering Geology》1993,35(3-4):229-235

The locations of a specific geological boundary and aquifer were predicted, prior to reaching them, by a reflection method and the measurement of geothermic temperature. The determination was performed during tunnelling work which passed through the Median Tectonic Line in central Japan. The reflection method procedure was as follows. A P-wave was produced on the tunnel face by a small blasting. The location of the velocity layer boundary was predicted by the travel time of the direct wave and the reflected wave. The geothermic temperature was measured by a thermocouple which was set in the borehole at the face. The location of the aquifer was predicted by the thermal deviation between the measured value and the theoretical value that was determined from a mean geothermal gradient. Also, a water quality survey is performed, discussing the quality of the fissure water. In addition, we were able to confirm, using the Seismic Tomography method, that the sheared zone found, was the layer including lens-shaped low-velocity zone. The methods considered proved to be simple and effective for geological prognosis from within the tunnel.  相似文献   

Early to Middle Miocene rotational tectonics of the Ou Backbone Range,northeast Japan          下载免费PDF全文

Jun Hosoi  Makoto Okada  Tomohiro Gokan  Kazuo Amano  Andrew James Martin 《Island Arc》2015,24(3):288-300

It is well known that a counterclockwise rotation occurred in the Miocene in northeast Japan. However, the detailed timing and mechanism of the rotation has been debated. Moreover, there has been no research about the relationship between rotational tectonics and the evolution of sedimentary basins. We carried out paleomagnetic and rock magnetic analyses in Nishiwaga Town, Iwate Prefecture, northeast Japan, where the stratigraphy and sedimentary basin formation have previously been clarified. We found that there was a counterclockwise rotational movement of about 45° at about 15 Ma. From our results and previous studies on the tectonics and sedimentary basin development, we are able to ascertain the following tectonic history and sedimentary basin evolution in this area: (i) before the rotational movement, sandstone and mudstone were deposited in a tranquil environment with no volcanic activity coupled with slow tectonic subsidence; (ii) between 16.4–15.1 Ma and 14 Ma, a counterclockwise rotation occurred with rapid tectonic subsidence and continuous explosive volcanism; (iii) at about 14 Ma, the counterclockwise rotation ended and there was a reduction in both subsidence and volcanism. This result shows the impact that rotational tectonics can have on sedimentary basin formation.  相似文献   

Multi-model ensemble estimation of volume transport through the straits of the East/Japan Sea     

Sooyeon Han  Naoki Hirose  Norihisa Usui  Yasumasa Miyazawa 《Ocean Dynamics》2016,66(1):59-76

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Flow behavior and microstructures of hydrous olivine aggregates at upper mantle pressures and temperatures     

Tomohiro?OhuchiEmail author  Takaaki?Kawazoe  Yuji?Higo  Akio?Suzuki 《Contributions to Mineralogy and Petrology》2017,172(8):65

Deformation experiments on olivine aggregates were performed under hydrous conditions using a deformation-DIA apparatus combined with synchrotron in situ X-ray observations at pressures of 1.5–9.8 GPa, temperatures of 1223–1800 K, and strain rates ranging from 0.8 × 10^?5 to 7.5 × 10^?5 s^?1. The pressure and strain rate dependencies of the plasticity of hydrous olivine may be described by an activation volume of 17 ± 6 cm³ mol^?1 and a stress exponent of 3.2 ± 0.6 at temperatures of 1323–1423 K. A comparison between previous data sets and our results at a normalized temperature and a strain rate showed that the creep strength of hydrous olivine deformed at 1323–1423 K is much weaker than that for the dislocation creep of water-saturated olivine and is similar to that for diffusional creep and dislocation-accommodated grain boundary sliding, while dislocation microstructures showing the [001] slip or the [001](100) slip system were developed. At temperatures of 1633–1800 K, a much stronger pressure effect on creep strength was observed for olivine with an activation volume of 27 ± 7 cm³ mol^?1 assuming a stress exponent of 3.5, water fugacity exponent of 1.2, and activation energy of 520 kJ mol^?1 (i.e., power-law dislocation creep of hydrous olivine). Because of the weak pressure dependence of the rheology of hydrous olivine at lower temperatures, water weakening of olivine could be effective in the deeper and colder part of Earth’s upper mantle.  相似文献   

Tectonic deformation buildup in folded mountain terrains in the October 23, 2004, Mid-Niigata earthquake     

Kazuo Konagai  Tomohiro Fujita  Takaaki Ikeda  Shigeki Takatsu 《Soil Dynamics and Earthquake Engineering》2009

The October 23, 2004, Mid-Niigata Earthquake jolted central Japan, causing serious damage in a mountainous region of Pliocene sedimentary rocks. Though aftershocks distribution showed a diffused pattern, it indicated that a blind-thrust fault having a NE–SW strike and inclined towards NW was the most causative. Tectonic deformation caused by this faulting was considered to be one of the causes of flooding that occurred about 8 months after the earthquake. Precise digital elevation models (DEMs) before and after the earthquake were obtained with stereoscopy for aerial photographs and laser imaging detection and ranging technology (LIDAR), respectively, and then compared to detect elevation changes and translations. Lastly, the changes of landforms due to landslides are excluded from the estimated deformations to obtain only the components of tectonic deformations of the ground surface.  相似文献   

Differences in the damage caused by hypoxia to the macrobenthic communities in source regions of hypoxic water and in regions with advected hypoxic water     

Shobu Ishimatsu  Tomohiro Komorita  Ryo Orita  Hiroaki Tsutsumi 《Journal of Oceanography》2018,74(6):607-617

The objective of this study was to determine the effects of transported hypoxic water on macrobenthic species composition in Isahaya Bay, Kyushu, Japan. To this end, we conducted a field survey of water quality, sediment quality, and the macrobenthic community across seasons. Hypoxic intensity, defined as the percentage of the time that a region exhibits hypoxic conditions [dissolved oxygen (DO) <?3.0 mg L^?1], was calculated for the summer period from July 1 to September 30, 2014 based on continuous monitoring data derived from six monitoring towers in the bay. Here, we discuss how the hypoxia-induced damage, defined as the change in the species compositions of the macrobenthic communities in the bay due to hypoxia, differs between the inner and middle regions of the bay (with muddy sediment) and the outer regions of the bay (with sandy sediment). A decrease in the density of macrobenthic species that was correlated to the period of lowest DO concentration (<?1.0 mg L^?1) was observed in the inner region of the bay. A large number of species disappeared from the macrobenthic community in the outer region after the DO concentration had dropped to its lowest level, even though this region presented the lowest hypoxic intensity (6.6%). The species that disappeared, including crustaceans and some polychaetes, were presumed to be sensitive to, and to have escaped from, hypoxia. Fewer species disappeared from the inner and intermediate regions of the bay, which had high hypoxic intensities of 14.0 and 26.7%, respectively, than from the outer region. The reason for this appeared to be a predominance of hypoxia-tolerant species in the inner and intermediate regions but not in the outer region. Our study suggests that estimating the effect of hypoxia in a spatially heterogeneous environment must be done with caution.  相似文献   

A partial melting study of an ordinary (H) chondrite composition with application to the unique achondrite Graves Nunataks 06128 and 06129          下载免费PDF全文

Tomohiro Usui  John H. Jones  David W. Mittlefehldt 《Meteoritics & planetary science》2015,50(4):759-781

Melting experiments of a synthesized, alkali‐bearing, H‐chondrite composition were conducted at ambient pressure with three distinct oxygen fugacity conditions (IW‐1, IW, and IW+2). Oxygen fugacity conditions significantly influence the compositions of partial melts. Partial melts at IW‐1 are distinctly enriched in SiO₂ relative to those of IW and IW+2 melts. The silica‐enriched, reduced (IW‐1) melts are characterized by high alkali contents and have silica‐oversaturated compositions. In contrast, the silica‐depleted, oxidized (≥IW) melts, which are also enriched in alkali contents, have distinctly silica‐undersaturated compositions. These experimental results suggest that alkali‐rich, felsic, asteroidal crusts as represented by paired achondrites Graves Nunataks 06128 and 06129 should originate from a low‐degree, relatively reduced partial melt from a parent body having near‐chondritic compositions. Based on recent chronological constraints and numerical considerations as well as our experimental results, we propose that such felsic magmatism should have occurred in a parent body that is smaller in size and commenced accreting later than those highly differentiated asteroids having basaltic crusts and metallic cores.  相似文献   

Seismic resistance capacity of beam–column connections in high‐rise buildings: E‐Defense shaking table test     

Yu‐Lin Chung  Takuya Nagae  Tomohiro Matsumiya  Masayoshi Nakashima 《地震工程与结构动力学》2011,40(6):605-622

A series of E‐Defense shaking table tests are conducted on a large‐scale test specimen that represents a high‐rise steel building. Two types of connections featuring the connection details commonly used in 1970s, in the early days of high‐rise construction in Japan, are adopted: the field‐welded connection consisting of welded unreinforced flanges and a bolted web type, and the shop‐welded connection in which the flanges and web are all‐welded to the column flange in the shop. To examine the seismic capacity of a total of 24 beam‐to‐column connections of the specimen, particularly when it is subjected to long‐period ground motion characterized not so much by large amplitude as by very many cycles of repeated loading, the test specimen is shaken repeatedly until the connections fractured. The test results indicate that a few of the field‐welded connections fractured from the bottom flange weld boundary in a relatively small cumulative rotation primarily due to the difficulties in ensuring the welding and inspection performance in the actual field welding. The shop‐welded connections are able to sustain many cycles of plastic rotation, with an averaged cumulative plastic rotation of 0.86 rad. Two shop‐welded connections exhibit ductile fractures but only after experiencing many cycles. The presence of RC floor slabs promotes the strain concentration at the toe of the weld access hole in the bottom flange by at least twice compared with the case without the slab, which had resulted in a decrease in the cumulative plastic rotation by about 50%. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Strength of single-crystal orthopyroxene under lithospheric conditions     

Tomohiro Ohuchi  Shun-ichiro Karato  Kiyoshi Fujino 《Contributions to Mineralogy and Petrology》2011,161(6):961-975

Creep strength of oriented orthopyroxene single crystals was investigated via shear deformation experiments under lithospheric conditions [P (pressure) = 1.3 GPa and T (temperature) = 973–1,373 K]. For the A-orientation (shear direction [001] on (100) plane), the samples have transformed completely to clinoenstatite and much of the deformation occurred after transformation. In contrast, for the B-orientation (shear direction [001] on (010) plane), samples remained orthoenstatite and deformation occurred through dislocation motion in orthoenstatite. The strength of orthopyroxene with these orientations is smaller than for olivine aggregates under all experimental conditions. Flow of the B-orientation samples is described by a power-law, and the pre-exponential constant, the apparent activation energy, and the stress exponent are determined to be A = 10^−9.5 s⁻¹·MPa^−4.2, Q = 114 kJ/mol and n = 4.2. However, for the A-orientation, the results cannot be fit by a single flow law and we obtained the following: A = 10^8.9 s⁻¹·MPa^−3.0, Q = 459 kJ/mol and n = 3.0 at high temperatures (≥1,173 K), and A = 10^−27.4 s⁻¹·MPa^−14.3, Q = 296 kJ/mol and n = 14.3 at low temperatures (<1,173 K). The stress exponent for the low-temperature regime is high, suggesting that deformation involves some processes where the activation energy decreases with stress such as the Peierls mechanism. Our study shows that orthopyroxene with these orientations is significantly weaker than olivine under the lithospheric conditions suggesting that orthopyroxene may reduce the strength of the lithosphere, although the extent to which orthopyroxene weakens the lithosphere depends on its orientation and connectivity.  相似文献   

Great earthquake at 7.3 ka inferred from tsunami deposits in the Sukumo Bay area,Southwestern Japan     

Futoshi Nanayama  Tomohiro Tsuji  Tatsuhiko Yamaguchi  Yasuo Kondo  Michiharu Ikeda  Toshimichi Nakanishi  Michiko Miwa  Chuki Hongo  Akira Furusawa  Mitsuhiro Kuwahata 《Island Arc》2021,30(1):e12422

Tsunami deposits in Kyushu Island, Southwestern Japan, have been attributed to the 7.3 ka Kikai caldera eruption, but their origin has not been confirmed. We analyzed an 83-cm-thick Holocene event deposit in the SKM core, obtained from incised valley fill in the coastal lowlands near Sukumo Bay, Southwestern Shikoku Island. We confirmed that the event deposit contains K-Ah volcanic ash from the 7.3 ka eruption. The base of the event deposit erodes the underlying inner-bay mud, and the deposit contains material from outside the local terrestrial and marine environment, including angular quartz porphyry from a small inland exposure, oyster shell debris, and a coral fragment. Benthic foraminifers and ostracods in the deposit indicate various habitats, some of which are outside Sukumo Bay. The sand matrix contains low-silica volcanic glass from the late stage of the Kikai caldera eruption. We also documented the same glass in an event deposit in the MIK1 core, from the incised Oyodo River valley in the Miyazaki Plain on Southeastern Kyushu. These two 7.3 ka tsunami deposits join other documented examples that are widely distributed in Southwestern Japan including the Bungo Channel and Beppu Bay in Eastern Kyushu, Tachibana Bay in Western Kyushu, and Zasa Pond on the Kii Peninsula as well as around the caldera itself. The tsunami deposits near the caldera have been divided into older and younger 7.3 ka tsunami deposits, the younger ones matching the set of widespread deposits. We attribute the younger 7.3 ka tsunami deposits to a large tsunami generated by a great interplate earthquake in the Northern part of the Ryukyu Trench and (or) the Western Nankai Trough just after the late stage of the Kikai caldera eruption and the older 7.3 ka tsunami deposits to a small tsunami generated by an interplate earthquake or Kikai caldera eruption.  相似文献