Metamorphic and cooling history of the Shimanto accretionary complex,Kyushu, Southwest Japan: Implications for the timing of out‐of‐sequence thrusting     

Hidetoshi Hara  Katsumi Kimura 《Island Arc》2008,17(4):546-559

Illite crystallinity, K–Ar dating of illite, and fission‐track dating of zircon are analyzed in the hanging wall (Sampodake unit) and footwall (Mikado unit) of a seismogenic out‐of‐sequence thrust (Nobeoka thrust) within the Shimanto accretionary complex of central Kyushu, southwest Japan. The obtained metamorphic temperatures, and timing of metamorphism and cooling, reveal the tectono‐metamorphic evolution of the complex, and related development of the Nobeoka thrust. Illite crystallinity data indicate that the Late Cretaceous Sampodake unit was metamorphosed at temperatures of around 300 to 310°C, while the Middle Eocene Mikado unit was metamorphosed at 260 to 300°C. Illite K–Ar ages and zircon fission‐track ages constrain the timing of metamorphism of the Sampodake unit to the early Middle Eocene (46 to 50 Ma, mean = 48 Ma). Metamorphism of the Mikado unit occurred no earlier than 40 Ma, which is the youngest depositional age of the unit. The Nobeoka thrust is inferred to have been active during about 40 to 48 Ma, as the Sampodake unit started its post metamorphic cooling after 48 Ma and was thrust over the Mikado unit at about 40 Ma along the Nobeoka thrust. These results indicate that the Nobeoka thrust was active for more than 10 million years.  相似文献   

Strong motion uncertainty determined from observed records by dense network in Japan   总被引：2，自引：1，他引：1  

Nobuyuki Morikawa  Tatsuo Kanno  Akira Narita  Hiroyuki Fujiwara  Toshihiko Okumura  Yoshimitsu Fukushima  Aybars Guerpinar 《Journal of Seismology》2008,12(4):529-546

The variation of ground motions at specific stations from events in six narrow areas was inspected by using K-NET and KiK-net records. A source-area factor for individual observation stations was calculated by averaging ratios between observed values for horizontal peak acceleration and velocity, as well as acceleration response spectra for 5% damping, and predicted values using a ground-motion model (usually known as an attenuation relation) by Kanno et al. (Bull Seismol Soc Am, 96:879–897, 2006). Standard deviations between observed and predicted amplitudes after the correction factor are less than 0.2 on the logarithmic scale and decrease down to around 0.15 in the short-period range. Intra-event standard deviation clearly increases with decreasing distance due to differing paths around near source area. Standard deviations may increase with amplitude or decrease with magnitude; however, both amplitude and magnitude of the data are strongly correlated with distance. The standard deviation calculated in this study is obviously much smaller than that of the original ground-motion model, as epistemic uncertainties are minimized by grouping ground motions at specific stations. This result indicates that the accuracy of strong ground motion prediction could be improved if ground-motion models for specified region are determined individually. For this to be possible, it is necessary to have dense strong-motion networks in high-seismicity regions, such as K-NET and KiK-net.  相似文献   

Improved Estimates of Wide-Ranging Sea Surface Temperature from GMS S-VISSR Data   总被引：1，自引：0，他引：1  

Shuichi Tanahashi  Hiroshi Kawamura  Toshihiko Matsuura  Tomoyuki Takahashi  Hiroyuki Yusa 《Journal of Oceanography》2000,56(3):345-358

We have developed an algorithm to estimate the wide-ranging Sea Surface Temperature (SST) data from the GMS-5 (Geostationary Meteorological Satellite) S-VISSR (Stretched-Visible Infrared Spin Scan Radiometer). Better SST estimates are realized by averaging the temporal variation of the VISSR calibration table and decreasing noise of the split-window terms using a spatial filter. The effects of the satellite zenith angle were examined in detail for better estimates, and VISSR-derived SSTs with root-mean-square (rms) error of 0.8 K were achieved using a new algorithm. The accuracy of SST estimates has been improved by using the temporal-spatial average of the split-window terms. Using the new techniques, we demonstrate that the hourly wide-ranging SST image data can be used to study the daily variations of SSTs in the Northern and Southern Pacific Oceans.  相似文献   

Simultaneous waveform inversion for three-dimensional Earth structure and earthquake source parameters considering a wide range of modal coupling     

Tatsuhiko Hara  & Robert J. Geller 《Geophysical Journal International》2000,142(2):539-550

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Landfill development in the urban fringe of Metro Manila     

Yuji Hara  Kazuhiko Takeuchi  Armando M. Palijon  Akinobu Murakami 《GeoJournal》2008,71(2-3):127-141

In low-lying areas of urban and suburban regions in Asia, the use of landfill has allowed urban land use to encroach onto watery landforms, such as back marshes, which were formerly used as rice fields. To improve understanding of the associations between land-use patterns and landfill development, we carried out a case study in the urban fringe of Metro Manila in the Philippines. We examined landfill volume derived from land-use change using GIS, and field surveyed qualitative aspects of the landfill used. We calculated the rate of application of landfill in low-lying housing development areas to be 5.0 × 10³ m³ km^?2 year^?1, most of which consisted of offsite disposal of construction waste or crushed rock produced by urban development and renewal on the adjoining uplands. The flow of fill material from offsite sources to onsite landfill development areas was on the basis of individual agreements between suppliers and developers.  相似文献   

Climate change at the monsoon/Westerly boundary in Northern Mexico   总被引：1，自引：0，他引：1  

S. E. Metcalfe  A. Bimpson  A. J. Courtice  S. L. O‘Hara  D. M. Taylor 《Journal of Paleolimnology》1997,17(2):155-171

Northern Mexico lies close to the present day boundary between mid-latitude (Westerly) and tropical (monsoonal) sources of moisture. Studies from the adjacent southwest USA have shown major changes in lake levels and vegetation distributions over the late Quaternary which have been interpreted in terms of significant variations in the relative strengths and positions of these climate systems. Palaeoclimatic data from this area have, however, left a number of unresolved questions which can only be answered by extending work into northern Mexico, closer to the major source of summer (monsoonal) rain, the Gulf of Mexico. Studies of palaeolake sediments from a series of hydrologically closed lake basins across a range of altitudes (1280 to 2200 m a.s.l.) in northern Chihuahua are in progress using geochemical, mineral magnetic, diatom and plant microfossil analyses. Preliminary results are presented from the Alta Babícora and Encinillas basins. The sites provide records of lacustrine deposition between >11000 and about 2500 yr BP. The diatom record from Babíora provides clear evidence for a deep water lake in this basin in the late glacial which persisted into the early Holocene. A dry episode coinciding with the timing of the Younger Dryas is recorded in Alta Babícora. Conditions wetter than present are indicated up to at least 7000 yr BP.  相似文献   

Compositional variations in spinel-hosted pargasite inclusions in the olivine-rich rock from the oceanic crust–mantle boundary zone     

Akihiro Tamura  Tomoaki Morishita  Satoko Ishimaru  Kaori Hara  Alessio Sanfilippo  Shoji Arai 《Contributions to Mineralogy and Petrology》2016,171(5):39

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Ocean bottom tiltmeter with acoustic data retrieval system implanted by a submersible     

Hideki Shimamura  Toshihiko Kanazawa 《Marine Geophysical Researches》1988,9(3):237-254

Sensitive Ocean Bottom Implanted Tiltmeters (OBITs) with a sophisticated data retrieval system have been developed in order to observe directly the subduction of oceanic lithosphere. The OBIT is the first long-term geophysical instrument which was designed to be deployed by a manned deep-sea submersible. When the OBIT is put on oceanic lithosphere which is bending and is about to subduct under a deep sea trench, the OBIT records the subduction by observing the tilt of the surface of the lithosphere. The OBIT system has a sensitivity of 10^-8 radian, which is enough to detect the ongoing subduction in months or years. The OBIT may give an answer to the question whether there are fluctuations in the subduction rate.Two OBITs were successfully deployed on a seaward slope of the Kuril Trench by the newly built French deep submersible, Nautile. The OBITs were installed on the northwest shoulder of Erimo seamount, at a depth of 3930 m, in the Kuril Trench. In order to attain stable long-term observations of crustal deformations, the sensing unit was cemented onto bare rock by mortar. We have not yet had an opportunity to recover the data.The life of the instruments is expected to be more than five years. An acoustic data transmission system has been developed for the OBIT data recovery. The stored data can be retrieved at any moment during the observation period, with no need to retrieve the instruments nor to interrupt the observation, by use of the acoustic system. The acoustic system has a high data transmission rate as well as extremely low power consumption. This will be the first long-term crustal deformation measurement on the sea floor.  相似文献   

Testing of a towed CTD     

Yukio Fujinawa  Yoshinobu Tsuji  Isao Watabe  Ken Sasaki  Masao Nomoto  Toshiaki Hara  Yoshito Tsuji 《Journal of Oceanography》1980,36(5):253-258

The results of laboratory and field experiments on a CTD measuring unit attached to a controllable towed body is described. It was verified that the three-dimensional distribution of salinity and temperature could be observed with sufficient accuracy (to 0.03 in salinity and to 0.01°C in temperature if proper correction is adopted) while cruising at up to 4 knots. A double integrated A/D converter is used to compensate for effects of extraneous environmental changes.  相似文献   

Current measurements with surface and subsurface drifters     

Keisuke Taira  Toshihiko Teramoto  Nobuyuki Shikama  Kensuke Takeuchi 《Journal of Oceanography》1978,34(2):73-77

An examination of behaviors of a subsurface drogue and a subsequent examination of current measurement with a drifter comprising the drogue as its important part are made in the channel between Oshima and Izu Peninsula. The drogue submerged to the anticipated depth of 300 m within 10 minutes after launching. Since then the drogue kept its depth and operated normally. From the comparison with the velocity measurement by the use of a currentmeter moored at a station in the vicinity of the drifter's track, it is verified that the drifter's motion well reflects the motion of a water parcel around the drogue.  相似文献