Geochemistry of the oldest MORB and OIB in the Isua Supracrustal Belt, southern West Greenland: Implications for the composition and temperature of early Archean upper mantle     

Tsuyoshi Komiya  Shigenori Maruyama  Takafumi Hirata  Hisayoshi Yurimoto  Susumu Nohda 《Island Arc》2004,13(1):47-72

Abstract Recent geological investigations of the Isua Supracrustal Belt (3.8 Ga), southern West Greenland, have suggested that it is the oldest accretionary complex on earth, defined by an oceanic plate‐type stratigraphy and a duplex structure. Plate history from mid‐oceanic ridge through plume magmatism to subduction zone has been postulated from analysis of the reconstructed oceanic plate stratigraphy in the accretionary complex. Comparison between field occurrence of greenstones in modern and ancient accretionary complexes reveals that two types of tholeiitic basalt from different tectonic settings, mid‐oceanic ridge basalt (MORB) and oceanic island basalt (OIB), occur. This work presents major, trace and rare earth element (REE) compositions of greenstones derived from Isua MORB and OIB, and of extremely rare relict igneous clinopyroxene in Isua MORB. The Isua clinopyroxenes (Cpx) have compositional variations equivalent to those of Cpx in modern MORB; in particular, low TiO₂ and Na₂O contents. The Isua Cpx show slightly light (L)REE‐depleted REE patterns, and the calculated REE pattern of the host magma is in agreement with that of Isua MORB. Analyses of 49 least‐altered greenstones carefully selected from approximately 1200 samples indicate that Isua MORB are enriched in Al₂O₃, and depleted in TiO₂, FeO*, Y and Zr at the given MgO content, compared with Isua OIB. In addition, Isua MORB show an LREE‐depleted pattern, whereas Isua OIB forms a flat REE pattern. Such differences suggest that the Early Archean mantle had already become heterogeneous, depending on the tectonic environment. Isua MORB are enriched in FeO compared with modern MORB. Comparison of Isua MORB with recent melting experiments shows that the source mantle had 85–87 in Mg? and was enriched in FeO. Potential mantle temperature is estimated to be approximately 1480°C, indicating that the Early Archean mantle was hotter by at most approximately 150°C than the modern mantle.  相似文献   

The estimation of wave height and wind speed persistence statistics from cumulative probability distributions     

S. Kuwashima  N. Hogben 《Coastal Engineering》1986,9(6)

Results are summarized of an investigation concerned with the development and validation of a method for estimating persistence statistics from cumulative probability distributions. Primary attention has been devoted to estimations of wave height persistence and the motivation has been the requirement to provide estimates of persistence statistics as an additional output for the wave climate synthesis programme called NMIMET which can provide data on a worldwide basis. The opportunity has also been taken to adapt the methods developed for application to estimation of wind speed persistence.A method due to Graham is taken as the starting point and is modified in the light of detailed examination of a number of measured data sets. The method thus derived is shown to be more reliable and much simpler to apply than Graham's method and to give results in good agreement with a range of measured data sets for both exceedance and non exceedance. The measured data used for validation include 2 sets in areas remote from the sites in UK waters used for most of the development. A comparison is also included between persistence statistics estimated using NMIMET output of wave height probabilities from visual wave data and results from measured data.  相似文献   

Joule heating and temperature in the upper atmosphere     

Susumu Kato 《Planetary and Space Science》1962,9(12):939-946

Joule heating has been shown to be very effective in increasing electronic temperature in the upper atmosphere. It is found theoretically that the electronic temperature can rise up to several thousands °K soon after certain ionospheric current disturbances occur, while the temperature of neutral particles increases only very slowly. Temperatures in various conditions have been computed and are found to be compatible with observation. It is also possible that the high electronic temperatures may explain the excitation of certain auroral glows.  相似文献   

Mechanical properties of cementitious sand and sand with small cyclic shear strain to assess aging effects on liquefaction     

Toyota  Hirofumi  Takada  Susumu 《Acta Geotechnica》2022,17(7):2825-2840

Liquefaction damage from earthquakes frequently indicates effects of sand aging on liquefaction resistance: Liquefaction damage in natural or aged reclaimed ground has been much less than that in young reclaimed ground. However, the mechanisms underlying aging effects remain unclear. Cementation and stress history of sand strongly influence aging effects: Cementation raises liquefaction resistance, whereas liquefaction history sometimes reduces liquefaction resistance. Small cyclic shear strain, from which the induced density change is almost negligible, was adopted as representing the stress history. To evaluate liquefaction resistance, initial shear modulus, and deformation characteristics of sand, we prepared specimens by adding cement and by applying a small cyclic shear strain. In cementitious sand, liquefaction resistance increased when cement contents exceeded 0.3% by mass. The initial shear modulus apparently increased at the same degree of cement addition as that which increased the liquefaction resistance. For sand with a small cyclic shear strain, the liquefaction resistance increased when the applied cyclic axial strain exceeded 0.01%. Application of small cyclic shear strain only slightly increased the initial shear modulus, but the linear elastic region tended to expand to greater shear strain. Shear properties of sand with small cyclic shear strain resembled those found for sand that had been consolidated for a long time.

  相似文献   

基于应变空间多机构CG模型的地震液化大变形数值分析     

周葛  刘汉龙  井合进  陈育民  飞田哲男 《岩土力学》2016,37(8):2417-2425

砂土液化导致的地基侧向大变形是地震中许多重要的工程设施和建筑物破坏的主要原因之一。简要介绍了可进行液化大变形分析的散粒体材料本构模型--应变空间多机构CG模型,基于FLIP ROSE程序平台,建立了预测和研究倾斜地基砂土液化导致侧向大变形的二维有限元数值分析方法。采用该模型对相同工况的土工动态离心模型试验进行了模拟,通过对比超孔隙水压力、剪切波水平加速度以及地基侧向位移发现,数值预测与试验结果吻合良好,从而验证了该有限元数值分析模型的可靠性。最后利用该数值分析模型预测了倾斜率不同的地基受到相同剪切波作用时,倾斜地基不同深度产生的侧向位移。预测结果显示,随着地基深度的减小,倾斜率对于地震液化导致倾斜地基侧向大变形的影响越来越显著。  相似文献   

Performance of HSC columns under severe cyclic loading     

Hakim Bechtoula  Susumu Kono  Fumio Watanabe  Youcef Mehani  Abderrahmane Kibboua  Mounir Naili 《Bulletin of Earthquake Engineering》2015,13(2):503-538

  相似文献   

Simulations of measures to control lava flows     

Eisuke Fujita  Masataka Hidaka  Akio Goto  Susumu Umino 《Bulletin of Volcanology》2009,71(4):401-408

We evaluated the quantitative effects of artificial barriers, water-cooling and guiding channels on lava flow using the lava simulation program LavaSIM. Lava flow is basically subject to the topography around the path, effusive rate and viscosity. To prevent damage due to lava flow, we conducted experiments in controlling the flow direction, velocity and temperature. The simulation demonstrated that artificial barriers can successfully change the direction of a lava flow and is more effective when placed nearly parallel to the flow direction at a point where the topography is not very steep, while a barrier placed perpendicular to the flow direction can only stop the flux temporarily, ultimately allowing the solidified crust to accumulate and causing the following mass to go over the barrier. The water-cooling trial was also effective in controlling the direction and temperature, although the amount of water was as much order as 10⁵ m³. The guiding channels successfully control the direction and inundated area but only in local areas.  相似文献   

Particle fluxes to the interior of the Southern Ocean in the Western Pacific sector along 170°W     

Susumu Honjo  Roger Francois  Steven Manganini  Jack Dymond  Robert Collier 《Deep Sea Research Part II: Topical Studies in Oceanography》2000,47(15-16)

An array of five bottom-tethered moorings with 19 PARFLUX time-series sediment trap at three depths (1 and 2 km below the surface, and 0.7 km above the sea-floor) was deployed in the western Pacific sector of the Southern Ocean, along 170°W. The five stations were selected to sample settling particles in the main hydrological zones of the Southern Ocean. The sampling period spanned 425 days (November 28, 1996–January 23, 1998) and was divided into 13 or 21 synchronized time intervals. A total of 174 sequential samples were recovered and analyzed to estimate fluxes of total mass (TMF), organic carbon, carbonate, biogenic silica, and lithogenic particles. The fluxes of biogenic material were higher than anticipated, challenging the notion that the Southern Ocean is a low-productivity region. Organic carbon fluxes at 1 km depth within the Polar Frontal Zone and the Antarctic Zone were relatively uniform (1.7–2.3 g m⁻² yr⁻¹), and about twice the estimated ocean-wide average (ca. 1 g m⁻² yr⁻¹). Carbonate fluxes were also high and uniform between the Subantarctic Front and ca. 64°S (11–13 g m⁻² yr⁻¹). A large fraction of the carbonate flux in the Antarctic Zone was due to the presence of pteropod shells. Coccoliths were found only to the north of the Polar Front, and calcium carbonate became the dominant phase in the Subantarctic Zone. In contrast, carbonate particles were nearly absent near 64°S. Latitudinal variations in biogenic silica fluxes were substantial. The large opal flux (57 g m⁻² yr⁻¹) measured in the Antarctic Zone suggests that opal productivity in this region has been previously underestimated and helps to explain the high sedimentary opal accumulation often found south of the Polar Front. Unlike biogenic material, fluxes of lithogenic particles were among the lowest measured in the open-ocean (0.12–0.05 g m⁻² yr⁻¹), reflecting a very low dust input.  相似文献   

Optimum strength ratio of hysteretic damper     

Kazuo Inoue  Susumu Kuwahara 《地震工程与结构动力学》1998,27(6):577-588

This paper deals with steel moment frames combined with hysteretic dampers. Specifically, it examines the strength of dampers required to minimize damage to moment frames under earthquake loading. The important structural variables are the ratio of the dampers' shear strength to the maximum resistance, termed β in this study, and the relative stiffness between the damper and the main frame, termed k. The equivalent viscous damping ratio of the entire structural system is affected by the quantities β and k and the ductility ratio of the main frame. The optimum dampers' strength ratio (β_opt), which maximizes the equivalent viscous damping ratio, was formulated as a function of k, and it was found that β_opt is independent of the ductility ratio of the main frame. Earthquake response analysis confirmed that damage to the main frame can be significantly reduced by hysteretic dampers and minimized at the value of β_opt. © 1998 John Wiley & Sons, Ltd.  相似文献   

Dilatancy of granular materials in a strain space multiple mechanism model     

Susumu Iai  Tetsuo Tobita  Osamu Ozutsumi  Kyohei Ueda 《国际地质力学数值与分析法杂志》2011,35(3):360-392

A granular material consists of an assemblage of particles with contacts newly formed or disappeared, changing the micromechanical structures during macroscopic deformation. These structures are idealized through a strain space multiple mechanism model as a twofold structure consisting of a multitude of virtual two‐dimensional mechanisms, each of which consists of a multitude of virtual simple shear mechanisms of one‐dimensional nature. In particular, a second‐order fabric tensor describes direct macroscopic stress–strain relationship, and a fourth‐order fabric tensor describes incremental relationship. In this framework of modeling, the mechanism of interlocking defined as the energy less component of macroscopic strain provides an appropriate bridge between micromechanical and macroscopic dilative component of dilatancy. Another bridge for contractive component of dilatancy is provided through an obvious hypothesis on micromechanical counterparts being associated with virtual simple shear strain. It is also postulated that the dilatancy along the stress path beyond a line slightly above the phase transformation line is only due to the mechanism of interlocking and increment in dilatancy due to this interlocking eventually vanishing for a large shear strain. These classic postulates form the basis for formulating the dilatancy in the strain space multiple mechanism model. The performance of the proposed model is demonstrated through simulation of undrained behavior of sand under monotonic and cyclic loading. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献