Evidence for 17th-century tsunamis generated on the Kuril–Kamchatka subduction zone, Lake Tokotan, Hokkaido, Japan     

Yuki Sawai   《Journal of Asian Earth Sciences》2002,20(8)

In the seventeenth century, two tsunamis that were generated by earthquakes on the Kuril–Kamchatka subduction zone inundated the eastern coast of Hokkaido, northern Japan. Stratigraphic evidence for these two tsunamis and related land-level change in coastal Hokkaido consists of two landward-thinning sand layers in the sediments of Lake Tokotan, a coastal lagoon on the Hokkaido coast. The marine origin of these sand layers is indicated by the presence of brackish–marine diatoms. The rarity and high degree of fragmentation of diatom valves suggests that the sands were transported in a short time over a considerable distance. Tsunamis at this site were probably generated by great earthquakes along the Kuril–Kamchatka Trench. Volcanic ash deposits lying just above the sands suggest that tsunamis occurred in the late 17th century. Tsunamis during the historic period are not recorded in Lake Tokotan, which suggests that the sand layers were deposited by tsunamis substantially larger than historic tsunamis.  相似文献   

Effects of structural walls on the elastic–plastic earthquake responses of frame–wall buildings     

Xhafer Kongoli  Tadao Minami  Yuki Sakai 《地震工程与结构动力学》1999,28(5):479-500

Effects of structural walls on the elastic–plastic earthquake response of short- to medium-height reinforced concrete buildings were investigated. The analytical model consists of independent lumped mass systems representing walls and frames connected at each floor. The wall structure undergoes flexural as well as shear deformation and fails in shear at relatively small story drifts, the frames deforming only in shear. As a measure of structural damage, the ductility factor responses of frame structures were calculated for different combinations of base shear coefficients for the frames and walls. In buildings with relatively weak frames, the installation of structural walls did not improve the large plastic response of the frames up to the point where the walls were unfailed in shear and the ductility factors of the frame structure were suddenly reduced to a very small number. For relatively strong frames, however, the response displacements decreased gradually as the number of walls increased, whether or not the walls failed. Empirical formulas for the required base shear coefficients of the walls and frames which gave a target ductility factor response also were derived for two particular groups of accelerograms. These equations should be of practical use in designing frame-wall type buildings and in retrofitting damaged buildings. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

The Brightness Temperature of the Quiet Solar Chromosphere at 2.6 mm     

Kazumasa Iwai  Masumi Shimojo  Shinichiro Asayama  Tetsuhiro Minamidani  Stephen White  Timothy Bastian  Masao Saito 《Solar physics》2017,292(1):22

The absolute brightness temperature of the Sun at millimeter wavelengths is an important diagnostic of the solar chromosphere. Because the Sun is so bright, measurement of this property usually involves the operation of telescopes under extreme conditions and requires a rigorous performance assessment of the telescope. In this study, we establish solar observation and calibration techniques at 2.6 mm wavelength for the Nobeyama 45 m telescope and accurately derive the absolute solar brightness temperature. We tune the superconductor–insulator–superconductor (SIS) receiver by inducing different bias voltages onto the SIS mixer to prevent saturation. Then, we examine the linearity of the receiver system by comparing outputs derived from different tuning conditions. Furthermore, we measure the lunar filled beam efficiency of the telescope using the New Moon, and then derive the absolute brightness temperature of the Sun. The derived solar brightness temperature is \(7700 \pm 310~\mbox{K}\) at 115 GHz. The telescope beam pattern is modeled as a summation of three Gaussian functions and derived using the solar limb. The real shape of the Sun is determined via deconvolution of the beam pattern from the observed map. Such well-calibrated single-dish observations are important for high-resolution chromospheric studies because they provide the absolute temperature scale that is lacking from interferometer observations.  相似文献   

Eccentric installation of splice plates for compressive strength improvement of rectangular hollow section braces     

Hiroshi Tagawa  Yuki Tanaka  Shohei Moriwake 《Bulletin of Earthquake Engineering》2018,16(11):5489-5502

Steel hollow section members are often applied as bracing in steel structures. Field-bolted connections of the slotted-in single splice plate and the gusset plate are popular because of their ease of construction. However, eccentricity between the splice and gusset plate axes reduces the compressive strength of the brace. This study proposes compressive strength improvement of rectangular hollow section braces using eccentrically installed splice plates such that the gusset plate axis coincides with the brace axis. To demonstrate the efficacy of the proposed concept, four compressive loading test results are examined in this study. Test results reveal the influences of splice plate eccentric installation on the brace compressive strength, the out-of-plane displacement, and the strain distribution. The proposed concept is effective for the brace with stiffened splice plates for inducing overall buckling with plastic hinges in the gusset plates. Variation of compressive strength is finally discussed based on the discrepancy between the brace axis and the axis of the plates in which the plastic hinges form at the overall buckling mode ends.  相似文献   

Seismic subsidence near the source region of the 1662 Kanbun Hyuganada Sea earthquake: Geochemical,stratigraphical, chronological,and paleontological evidences in Miyazaki Plain,southwest Japan     

Masakazu Niwa  Takanobu Kamataki  Hideki Kurosawa  Yoko Saito‐Kokubu  Masafumi Ikuta 《Island Arc》2020,29(1)

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Estimating the thickness of a faulted mechanical layer based on fault spacing: An example from Miyako‐jima Island,southern Ryukyu Arc,Japan     

Sumire Maeda  Makoto Otsubo  Daisuke Asahina  Yuki Furuno 《Island Arc》2020,29(1)

The thickness of the mechanical layer that hosts a group of faults can be estimated from the spacing of saturated faults (i.e. the constant spacing between faults when the fault system is fully developed and has attained its final fault density). We measured fault spacing for a group of saturated active normal faults on Miyako‐jima Island (southern Ryukyu Arc, Japan) and estimated the thickness of the faulted mechanical layer. The measured fault spacing is 1.30 ±0.14 km, and the thickness of the mechanical layer is < 3 km, which is the upper limit of the seismogenic zone. This faulted mechanical layer corresponds to a sedimentary layer in which earthquakes cannot occur. Results indicate that the shallow (< 3 km depth) normal faults on Miyako‐jima Island do not have the potential to cause medium‐size earthquakes as individual faults. The origin of the shallow normal faults might be related to the presence of a larger‐scale, deeper fault. The results indicate that fault spacing provides important information on the potential magnitude of earthquakes associated with active faults.  相似文献   

Geochemical characteristics of zircons in the Ashizuri A‐type granitoids: An additional granite topology tool for detrital zircon studies          下载免费PDF全文

Yusuke Sawaki  Kazue Suzuki  Hisashi Asanuma  Satoki Okabayashi  Kentaro Hattori  Takuya Saito  Takafumi Hirata 《Island Arc》2017,26(6)

Zircon is resistant to alteration over a wide range of geological environments, and isotopic ratios within the mineral provide constraints on ages and their parental magmas. Trace element compositions in zircon are also expected to reflect those of their parent magmas, and have a potential as essential indicators for their host rocks. Because most detrital zircons that accumulate at river mouths are derived primarily from granitoids, the classification of zircon within granitoids is potentially meaningful. This study employs the conventional classification scheme of granites (I‐, S‐, M‐, and A‐types). To clarify geochemical characteristics of zircons in A‐type granites, trace element compositions of zircons extracted from the A‐type Ashizuri granitoids were examined. Zircons from the Ashizuri granitoids commonly show enrichments of heavy rare earth elements and positive Ce anomalies, indicating that these zircons were igneous in origin. In addition, zircons in these A‐type granites are characterized by enrichments of Nb, Y, Ta, Th, and U and strong negative Eu anomalies, which exhibit good positive correlations with those in their whole rocks. This fact indicates that these signatures in zircons reflect well those in their parental bodies and are useful in identifying zircons derived from A‐type granite. Based on compilations of available data, zircons from A‐type granites can be clearly discriminated from other‐types of granites within Nb/Sr–Eu anomaly, U/Sr–Eu anomaly, Nb/Sr–U/Sr, and Nb/Sr–Ta/Sr cross‐plots. All indices used in these diagrams were selected based on the geochemical features of both zircon and whole rock of A‐type granites. Application of these discrimination diagrams to detrital zircons will likely provide further insights. For example, some Hadean detrital zircons plot in similar fields to A‐type granites, implying the existence of A‐type magmatism in the Earth's earliest history.  相似文献   

Constraining sediment provenance for tsunami deposits using distributions of grain size and foraminifera from the Kujukuri coastline and shelf,Japan     

Jessica E. Pilarczyk  Yuki Sawai  Dan Matsumoto  Yuichi Namegaya  Naohisa Nishida  Ken Ikehara  Osamu Fujiwara  Chris Gouramanis  Tina Dura  Benjamin P. Horton 《Sedimentology》2020,67(3):1373-1392

Tsunami deposits preserved in the geological record provide a more comprehensive understanding of their patterns of frequency and intensity over longer timescales; but recognizing tsunami deposits can prove challenging due to post-depositional changes, lack of contrast between the deposits and surrounding sedimentary layers, and differentiating between tsunami and storm deposition. Modern baseline studies address these challenges by providing insight into modern spatial distributions that can be compared with palaeotsunami deposits. This study documents the spatial fingerprint of grain size and foraminifera from Hasunuma Beach and the Kujukuri shelf to provide a basis from which tsunami deposits can be interpreted. At Hasunuma Beach, approximately 50 km east of Tokyo, the spatial distribution of three common proxies (foraminiferal taxonomy, foraminiferal taphonomy and sediment grain size) for tsunami identification were mapped and clustered using Partitioning Around Medoids cluster analysis. Partitioning Around Medoids cluster analysis objectively discriminated two coastal zones corresponding to onshore and offshore sample locations. Results show that onshore samples are characterized by coarser grain sizes (medium to coarse sand) and higher abundances of Pararotalia nipponica (27 to 63%) than offshore samples, which are characterized by finer grain sizes (fine to medium sand), lower abundances of Pararotalia nipponica (2 to 19%) and Ammonia parkinsoniana (0 to 10%), higher abundances of planktonics (15 to 58%) and species with fragile tests including Uvigerinella glabra. When compared to grain-size and foraminiferal taxonomy, foraminiferal taphonomy; i.e. surface condition of foraminifera, a proxy not commonly used to identify tsunami deposits, was most effective in discriminating modern coastal zones (identified supratidal, intertidal and offshore environments) and determining sediment provenance for tsunami deposits at Kujukuri. This modern baseline study assists the interpretation of tsunami deposits in the geological record because it provides a basis for sediment provenance to be determined.  相似文献   

Recent and historical tsunami deposits from Lake Tokotan,eastern Hokkaido,Japan, inferred from nondestructive,grain size,and radioactive cesium analyses     

Shinozaki  Tetsuya  Sawai  Yuki  Ito  Kazumi  Hara  Junko  Matsumoto  Dan  Tanigawa  Koichiro  Pilarczyk  Jessica E. 《Natural Hazards》2020,103(1):713-730

Geological evidence of recent tsunamis from sediment samples collected from Lake Tokotan, a coastal lagoon in eastern Hokkaido, northern Japan, was detected using computed tomography (CT) and soft X-ray images, grain size, and radionuclide profiles. Initial field observations revealed that sediments had no discernable sedimentary structures at the top of the core. However, results of CT imaging, soft X-ray, and grain size analyses show evidence for three invisible sand layers that are intercalated with mud layers. These sand layers exhibit trends of landward fining and thinning. Furthermore, the distribution of sand layers was limited to the center and seaward parts of the lake. Vertical profiles of cesium and lead concentrations in combination with recent eyewitness accounts indicated that these sand layers are correlated with the 1973 Nemuro-oki, 1960 Chilean, and 1952 Tokachi-oki tsunami events. The deeper part of the sediment cores includes three volcanic ash layers and three prehistoric coarse sand layers. The prehistoric layers are correlated with unusually large tsunamis that were geologically identified in previous studies from eastern Hokkaido. These findings suggest that nondestructive techniques, in combination with radionuclide analysis, allow for detection of frequent but faint tsunami deposits. This technique allows for an improved understanding of the history of tsunami inundation in Lake Tokotan and of other locations for which stratigraphic evidence for faint tsunamis layers is not readily apparent from field assessments.

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Influence of non-photosynthetic pigments on light absorption and quantum yield of photosynthesis in the western equatorial Pacific and the Subarctic North Pacific     

Anil Kumar Vijayan  Takashi Yoshikawa  Shigeki Watanabe  Hiroaki Sasaki  Kazuhiko Matsumoto  Sei-Ichi Saito  Shigenobu Takeda  Ken Furuya 《Journal of Oceanography》2009,65(2):245-258

Regional variations in the contribution of non-photosynthetic pigments (ā _np^*) to the total light absorption of phytoplankton (ā _ph^*) and its influence on the maximum quantum yield of photosynthesis (φ _m) were investigated. In the western equatorial Pacific, the surface ā _np^* : ā _ph^* ratio was higher in the western warm pool than that in the upwelling region. This difference appears to be attributable to severe nitrate depletion and higher percentage of prokaryotes, which can accumulate very high concentrations of zeaxanthin in the western warm pool. In the subarctic North Pacific, the ā _np^* : ā _ph^* ratio was expected to be higher in the Alaskan Gyre where the thermocline is sharper and iron limitation may possibly be more severe than in the Western Subarctic Gyre. However, the ratio was actually higher in the Western Subarctic Gyre, contradictory to our expectations. This east-west variation appears to be attributable to changes in the taxonomic composition; cyanobacteria were more abundant in the Western Subarctic Gyre. The values of ā _np^* : ā _ph^* and its vertical variations were relatively small in the subarctic North Pacific compared to those in the western equatorial Pacific. These inter-regional variations appear to be attributable to the lower solar radiation intensity, smaller percentage of cyanobacteria, and relatively strong vertical mixing in the subarctic North Pacific. The spatial variations in ā _np^* : ā _ph^* significantly influence φ _m. In comparison with φ _m based on the total light absorption (φ _{m ph}), the values corrected for the contribution of non-photosynthetic pigments (φ _{m ps}) showed an increase in both the western equatorial Pacific and the subarctic North Pacific.  相似文献