Effect of topography and subsurface inhomogeneity on seismic rayleigh waves     

Akira Ohtsuki  Hiroshi Yamahara  Kasaburo Harumi 《地震工程与结构动力学》1984,12(1):37-58

The effect of topography and subsurface inhomogeneity on surface motion is investigated in the case of Rayleigh waves. In the previous paper, the same effect was investigated in the case of SV waves. Several types of topography, such as cliffs both with and without a soft layer at the foot of the slope, are considered. Computations are made using a new hybrid method combining a particle model with a finite element method. In cases of harmonic Rayleigh waves, surface motions with amplitudes as large as 1.5 to 5 times the horizontal surface displacement of the incident Rayleigh waves are produced near the slope and the sloping interface. When a Rayleigh wave propagating through a hard single-layered ground encounters a sloping interface where hard ground and soft ground make contact with each other, Rayleigh waves having two different, phase velocities are produced and they correspond to the fundamental mode, and the first mode determined by Haskell's method. In addition, the transient response when Rayleigh waves propagate through the cliff is also simulated. Assuming the vertical component of the Tokachi-oki Earthquake (1968) measured on the surface to be a Rayleigh wave, the incident Rayleigh wave can be obtained by a Fourier synthesis of eigenfunctions of Rayleigh waves.  相似文献   

Paleoposition of Southwest Japan at 16 Ma: Implication from paleomagnetism of the Miocene Ichishi Group     

Akira Hayashida  Yoshihiko Ito 《Earth and Planetary Science Letters》1984,68(2):335-342

New paleomagnetic data from shallow-marine sediments of the Ichishi Group suggest a clockwise tectonic rotation of Southwest Japan in the Middle Miocene. Samples have been collected from mud or tuff layers at 17 sites. Stability of remanent magnetization has been examined by using alternating field and thermal demagnetization. The polarity sequence, composed of four normal and seven reversed polarity sites, is correlated to Polarity Epoch 16 (15.2–17.6 Ma), based on micropaleontological assignment of the upper Ichishi Group to Blow's Zone N8. The mean paleomagnetic direction of the 11 sites shows an anomalous declination toward the northeast. This result suggests that Southwest Japan was subjected to a clockwise rotation through 45° since 16 Ma. The clockwise rotation can be explained by the drift of Southwest Japan associated with the spreading of the Japan Sea during the Middle Miocene.  相似文献   

Garnet-ilmenite-perovskite transitions in the system Mg₄Si₄O₁₂-Mg₃Al₂Si₃O₁₂ at high pressures and high temperatures: phase equilibria, calorimetry and implications for mantle structure     

Masaki Akaogi  Akira TanakaEiji Ito 《Physics of the Earth and Planetary Interiors》2002,132(4):303-324

Phase relations in the system Mg₄Si₄O₁₂-Mg₃Al₂Si₃O₁₂ were examined at pressures of 19-27 GPa and relatively low temperatures of 800-1000 °C using a multianvil apparatus to clarify phase transitions of pyroxene-garnet assemblages in the mantle. Both of glass and crystalline starting materials were used for the experiments. At 1000 °C, garnet solid solution (s.s.) transforms to aluminous ilmenite s.s. at 20-26 GPa which is stable in the whole compositional range in the system. In Mg₄Si₄O₁₂-rich composition, ilmenite s.s. transforms to a single-phase aluminous perovskite s.s., while Mg₃Al₂Si₃O₁₂-rich ilmenite s.s. dissociates into perovskite s.s. and corundum s.s. These newly determined phase relations at 1000 °C supersede preliminary phase relations determined at about 900 °C in the previous study. The phase relations at 1000 °C are quite different from those reported previously at 1600 °C where garnet s.s. transforms directly to perovskite s.s. and ilmenite is stable only very close to Mg₄Si₄O₁₂. The stability field of Mg₃Al₂Si₃O₁₂ ilmenite was determined at 800-1000 °C and 25-27 GPa by reversed phase boundaries. In ilmenite s.s., the a-axis slightly increases but the c-axis and molar volume decrease substantially with increasing Al₂O₃ content. Enthalpies of ilmenite s.s. were measured by differential drop-solution calorimetry method using a high-temperature calorimeter. The excess enthalpy of mixing of ilmenite s.s. was almost zero within the errors. The measured enthalpies of garnet-ilmenite and ilmenite-perovskite transitions at 298 K were 105.2±10.4 and 168.6±8.2 kJ/mol, respectively, for Mg₄Si₄O₁₂, and 150.2±15.9 and 98.7±27.3 kJ/mol, respectively, for Mg₃Al₂Si₃O₁₂. Thermodynamic calculations using these data give rise to phase relations in the system Mg₄Si₄O₁₂-Mg₃Al₂Si₃O₁₂ at 1000 and 1600 °C that are generally consistent with those determined experimentally, and confirm that the single-phase field of ilmenite expands from Mg₄Si₄O₁₂ to Mg₃Al₂Si₃O₁₂ with decreasing temperature. The earlier mentioned phase relations in the simplified system as well as those in the Mg₂SiO₄-Fe₂SiO₄ system are applied to estimate mineral proportions in pyrolite as a function of depth along two different geotherms: one is a horizontally-averaged temperature distribution in a normal mantle, and the other being 600 °C lower than the former as a possible representative geotherm in subducting slabs. Based on the previously described estimated mineral proportions versus depth along the two geotherms, density and compressional and shear wave velocities are calculated as functions of depth, using available mineral physics data. Along a normal mantle geotherm, jumps of density and velocities at about 660 km corresponding to the post-spinel transition are followed by steep gradients due to the garnet-perovskite transition between 660 and 710 km. In contrast, along a low-temperature geotherm, the first steep gradients of density and velocities are due to the garnet-ilmenite transition between 610 and 690 km. This is followed by abrupt jumps at about 690 km for the post-spinel transition, and steep gradients between 700 and 740 km that correspond to the ilmenite-perovskite transition. In the latter profile along the low-temperature geotherm, density and velocity increases for garnet-ilmenite and ilmenite-perovskite transitions are similar in magnitude to those for the post-spinel transition. The likely presence of ilmenite in cooler regions of subducting slabs is suggested by the fact that the calculated velocity profiles along the low-temperature geotherm are compatible with recent seismic observations indicating three discontinuities or steep velocity gradients at around 600-750 km depth in the regions of subducting slabs.  相似文献   

The Meteoritical Bulletin,No. 92, 2007 September     

Harold C. Connolly  Caroline Smith  Gretchen Benedix  Luigi Folco  Kevin Righter  Jutta Zipfel  Akira Yamaguchi  Hasnaa Chennaoui Aoudjehane 《Meteoritics & planetary science》2007,42(9):1647-1694

Abstract— In this edition of The Meteoritical Bulletin, 1394 recognized meteorites are reported, 27 from specific locations within Africa, 133 from Northwest Africa, 1227 from Antarctica (from ANSMET, PNRA, and PRIC expeditions), and 7 from Asia. The Meteoritical Bulletin announces the approval of four new names series by the Nomenclature Committee of the Meteoritical Society, two from Africa and one from Asia, including Al Haggounia, from Al Haggounia, Morocco, which is projected to be on the order of 3 metric tons of material related to enstatite chondrites and aubrites. Approved are two falls from Africa, Bassikounou (Mauritania) and Gashua (Nigeria). Approved from areas other than Antarctica are one lunar, two Martian, 32 other achondrites, three mesosiderites, two pallasites, one CM, two CK, one CR2, two CV3, one CR2, and four R chondrites. The Nomenclature Committee of the Meteoritical Society announces 48 newly approved relict meteorites from two new name series, Österplana and Gullhögen (both from Sweden).  相似文献   

Geology of the Gorny Altai subduction–accretion complex, southern Siberia: Tectonic evolution of an Ediacaran–Cambrian intra-oceanic arc-trench system   总被引：1，自引：0，他引：1  

Tsutomu Ota  Atsushi Utsunomiya  Yuko Uchio  Yukio Isozaki  Mikhail M. Buslov  Akira Ishikawa  Shigenori Maruyama  Koki Kitajima  Yoshiyuki Kaneko  Hiroshi Yamamoto  Ikuo Katayama   《Journal of Asian Earth Sciences》2007,30(5-6):666-695

The Gorny Altai region in southern Siberia is one of the key areas in reconstructing the tectonic evolution of the western segment of the Central Asian Orogenic Belt (CAOB). This region features various orogenic elements of Late Neoproterozoic–Early Paleozoic age, such as an accretionary complex (AC), high-P/T metamorphic (HP) rocks, and ophiolite (OP), all formed by ancient subduction–accretion processes. This study investigated the detailed geology of the Upper Neoproterozoic to Lower Paleozoic rocks in a traverse between Gorno-Altaisk city and Lake Teletskoy in the northern part of the region, and in the Kurai to Chagan-Uzun area in the southern part. The tectonic units of the studied areas consist of (1) the Ediacaran (=Vendian)–Early Cambrian AC, (2) ca. 630 Ma HP complex, (3) the Ediacaran–Early Cambrian OP complex, (4) the Cryogenian–Cambrian island arc complex, and (5) the Middle Paleozoic fore-arc sedimentary rocks. The AC consists mostly of paleo-atoll limestone and underlying oceanic island basalt with minor amount of chert and serpentinite. The basaltic lavas show petrochemistry similar to modern oceanic plateau basalt. The 630 Ma HP complex records a maximum peak metamorphism at 660 °C and 2.0 GPa that corresponds to 60 km-deep burial in a subduction zone, and exhumation at ca. 570 Ma. The Cryogenian island arc complex includes boninitic rocks that suggest an incipient stage of arc development. The Upper Neoproterozoic–Lower Paleozoic complexes in the Gorno-Altaisk city to Lake Teletskoy and the Kurai to Chagan-Uzun areas are totally involved in a subhorizontal piled-nappe structure, and overprinted by Late Paleozoic strike-slip faulting. The HP complex occurs as a nappe tectonically sandwiched between the non- to weakly metamorphosed AC and the OP complex. These lithologic assemblages and geologic structure newly documented in the Gorny Altai region are essentially similar to those of the circum-Pacific (Miyashiro-type) orogenic belts, such as the Japan Islands in East Asia and the Cordillera in western North America. The Cryogenian boninite-bearing arc volcanism indicates that the initial stage of arc development occurred in a transient setting from a transform zone to an incipient subduction zone. The less abundant of terrigenous clastics from mature continental crust and thick deep-sea chert in the Ediacaran–Early Cambrian AC may suggest that the southern Gorny Altai region evolved in an intra-oceanic arc-trench setting like the modern Mariana arc, rather than along the continental arc of a major continental margin. Based on geological, petrochemical, and geochronological data, we synthesize the Late Neoproterozoic to Early Paleozoic tectonic history of the Gorny Altai region in the western CAOB.  相似文献   

Simplified seismic design approach for steel portal frame piers with hysteretic dampers     

Zhiyi Chen  Hanbin Ge  Akira Kasai  Tsutomu Usami 《地震工程与结构动力学》2007,36(4):541-562

A simplified seismic design procedure for steel portal frame piers installed with hysteretic dampers is proposed, which falls into the scope of performance‐based design philosophy. The fundamental goal of this approach is to design a suite of hysteretic damping devices for existing and new bridge piers, which will assure a pre‐defined target performance against future severe earthquakes. The proposed procedure is applicable to multi‐degree‐of‐freedom systems, utilizing an equivalent single‐degree‐of‐freedom methodology with nonlinear response spectra (referred to as strength‐demanded spectra) and a set of formulae of close‐form expressions for the distribution of strength and stiffness produced in the structure by the designed hysteretic damping devices. As an illustrative example, the proposed procedure is applied to a design of a simple steel bridge pier of portal frame type with buckling‐restrained braces (one of several types of hysteretic dampers). For the steel portal frame piers, an attempt is made to utilize not only the displacement‐based index but also the strain‐based index as pre‐determined target performance at the beginning of design. To validate this procedure, dynamic inelastic time‐history analyses are performed using the general‐purpose finite element program ABAQUS. The results confirm that the proposed simplified design procedure attains the expected performance level as specified by both displacement‐based and strain‐based indices with sufficient accuracy. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Spatial gradient analysis of urban green spaces combined with landscape metrics in Jinan City of China     

KONG Fan-hua Nobukazu NAKAGOSHI YIN Hai-wei Akira KIKUCHI 《中国地理科学(英文版)》2005,15(3):254-261

1IN T R O D U C T IO NUrban green spaces can be consideredas the outdoorplacesintheurban covered with significanatmounts ofvegetation,naturalor manmade,as opposed to areasthatare paved or having buildingon them(JIM andC HEN,2003;SHIVANAND and SUZANA,2005)…  相似文献   

Geneses of High Chlorine and Silver–Lead–Zinc–Mineralized Granitoids in Tsushima, Japan     

Shunso ISHIHARA  Akira IMAI 《Resource Geology》2000,50(3):169-178

Abstract: Miocene granitoids of the Tsushima Islands have unique characteristics that cannot be seen in other major granitic plutons in the Japanese Islands as follows: (1) They are granitic in composition but contain synplutonic mafic dikes, abundant mafic enclaves, and intermediate facies between granite and mafic enclaves. (2) They are mixture of magnetite‐bearing and –free facies, but generally magnetite‐free in the marginal part. (3) They are high in K₂O content (K₆₅=3. 1) and intermediate in normative corundum (C₆₅=0. 1) and δ¹⁸O value (+9% at SiO₂ 70 %), which may be comparable with those of the Miocene Outer Zone granitoids. (4) Yet the initial Sr ratio is low as 0. 7037. (5) They are high in Cl and S, which occur in fluid inclusions and as pyrrhotite>pyrite, respectively. Two genetic models are considered for the source of the unique granitoid magmas: the continental crust or the upper mantle fertilized with Si, K and ¹⁸O. The latter may be the case for the Tsushima granitoids, because of the low initial Sr ratio. The age of the granitoids (16 Ma) indicates the magmatism related to the opening of the Sea of Japan. It is suggested that both basaltic and granitic magmas were generated in the continental lithosphere under an extensional tectonic setting; the two magmas could have been partly mingled. The mingled magma was originally an oxidized type, but reduced during the emplacement by repeated inflow of S and C‐bearing gases from the pelitic wall rocks. Because of the reduction, SO₃ sulfur is almost nil in the rock‐forming apatite, and most of sulfur remained in fluid phase of the magma as reduced species. Cl content was high in the original magma and concentrated in the fluid phase of the residual system which dissolved silver, lead and zinc metals. Such a fluid migrated into the Taishu fracture systems, as the magma crystallized, and formed the silver–lead–zinc deposits.  相似文献   

Sulfur Isotope Study and Re-examination of Ore Mineral Assemblage of the Hol Kol and the Tul Mi Chung Skarn-type Copper–Gold Deposits of the Suan Mining District, Korean Peninsula     

Akira Imai  Shinichi Anan 《Resource Geology》2000,50(4):213-228

Abstract: Ore specimens collected by the late Professor Takeo Watanabe from the Hol Kol and the Tul Mi Chung deposits, Suan mining district, Korean peninsula, were examined. In addition, measurements of sulfur isotopic ratio of ores and preliminary fluid inclusion microthermometry were carried out. Ores from the New orebody of the Hol Kol deposit consist mainly of bornite, wittichenite and chalcopyrite presently, which exhibit lamellae intergrowth texture, associated with native bismuth and electrum. Bismuthian bornite solid solution is considered to be a principal initial phases, while native bismuth was nucleated as molten bismuth melt initially. The occurrence of cubanite, miharaite, carrollite, siegenite, hessite and geikielite are recognized from the New orebody. Ores from the Eastern orebody of the Hol Kol deposit consist chiefly of chalcopyrite, occasionally associated with trace amounts of pyrrhotite, pyrite, bismuthinite and rare tellurobismuthite, while an ore specimen from the Western orebody consists mainly of sphalerite associated with chalcopyrite, pyrite and galena. Ores from the Tul Mi Chung deposit consist mainly of chalcopyrite and pyrite, occasionally associated with magnetite, sphalerite, galena and rare molybdenite. Some portions of magnetite are revealed to be silician magnetite. Sulfur fugacity is supposed to be below the stability field of bismuthinite in the New orebody. A reducing condition is suggested by the occurrence of geikielite without Fe³⁺ content. The sulfur and oxygen fugacities for the Eastern and Western orebodies of the Hol Kol deposit and for the Tul Mi Chung deposit were higher than the New orebody of the Hol Kol deposit. On the other hand, the Suan granite (porphyritic granodiorite) and the Chil Sing Dai granite (biotite granite porphyry) from the Hol Kol area can be classified as weakly magnetic magnetite‐series. Polyphase fluid inclusions are observed in gangue diopside associated with Cu ore of two specimens. The dissolution temperatures of daughter crystals are 394±26°C and 442±45°C, while the disappearing temperatures of vapor bubble were 475±25°C and > 500°C. Highly saline fluids were responsible for the mineralization at the Hol Kol deposit. The δ³⁴S values of ore sulfides of the Hol Kol and the Tul Mi Chung deposit range from +11. 5% to +16. 1%, having anomalous lower values mainly from the Tul Mi Chung deposit. Such anomalous lower 6³⁴S values can be caused by isotopic fractionation against oxidized sulfur species. The δ³⁴S value of bulk sulfur in the ore solutions responsible for the Hol Kol and the Tul Mi Chung deposit is estimated to be +13.5±2.5‰.  相似文献   

Short‐term flood inundation prediction using hydrologic‐hydraulic models forced with downscaled rainfall from global NWP          下载免费PDF全文

Do Hoai Nam  Dang Thanh Mai  Keiko Udo  Akira Mano 《水文研究》2014,28(24):5844-5859

A short‐term flood inundation prediction model has been formulated based on the combination of the super‐tank model, forced with downscaled rainfall from a global numerical weather prediction model, and a one‐dimensional (1D) hydraulic model. Different statistical methods for downscaled rainfall have been explored, taking into account the availability of historical data. It has been found that the full implementation of a statistical downscaling model considering physically‐based corrections to the numerical weather prediction model output for rainfall prediction performs better compared with an altitudinal correction method. The integration of the super‐tank model into the 1D hydraulic model demonstrates a minimal requirement for the calibration of rainfall–runoff and flood propagation models. Updating the model with antecedent rainfall and regular forecast renewal has enhanced the model's capabilities as a result of the data assimilation processes of the runoff and numerical weather prediction models. The results show that the predicted water levels demonstrate acceptable agreement with those measured by stream gauges and comparable to those reproduced using the actual rainfall. Moreover, the predicted flood inundation depth and extent exhibit reasonably similar tendencies to those observed in the field. However, large uncertainties are observed in the prediction results in lower, flat portions of the river basin where the hydraulic conditions are not properly analysed by the 1D flood propagation model. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献