Field measurements of absolute gravity in East Antarctica     

Koichiro Doi  Hideaki Hayakawa  Takahito Kazama  Toshihiro Higashi  Shingo Osono  Yoichi Fukuda  Jun Nishijima  Yuichi Aoyama  Junichi Ueda 《极地研究(英文版)》2013,(4):339-343

Abstract This paper reports the results of field-based absolute gravity measurements aimed at detecting gravity change and crustal displacement caused by glacial isostatic adjustment. The project was initiated within the framework of the 53rd Japanese Antarctic Research Expedition （JARE53）. Absolute gravity measurements, together with GPS measurements, were planned at several outcrops along the Prince Olav Coast and S6ya Coast of East Antarctica, including at Syowa Station. Since the icebreaker Shirase （AGB 5003） was unable to moor alongside Syowa Station, operations were somewhat restricted during JARE53. However, despite this setback, we were able to complete measurements at two sites： Syowa Station and Langhovde. The absolute gravity value at the Syowa Station IAGBN （A） site, observed using an FG-5 absolute gravimeter （serial number 210; FG-5 #210）, was 982 524 322.7＋0.1 ktGal, and the gravity change rate at the beginning of 2012 was -0.26 gGal.a-1. An absolute gravity value of 982 535 584.2~0.7 ktGal was obtained using a portable A-10 absolute gravimeter （serial number 017; A-10 #017） at the newly located site AGS01 in Langhovde.  相似文献   

Hemispherical distribution of CO above the Venus’ clouds by ground-based 2.3 μm spectroscopy     

N. Iwagami  T. Yamaji  S. Ohtsuki  G.L. Hashimoto 《Icarus》2010,207(2):558-563

The abundance of carbon monoxide in the Venus’ dayside atmosphere above the clouds was measured by ground-based 2.3 μm spectroscopy for 4 days. The hemispherical distributions found show no significant latitudinal or longitudinal structure. The disc-averaged mixing ratio of 58 ± 17 ppm found at a representative height of 62-67 km is consistent with previous measurements. Such a flat distribution of CO abundance above the clouds seems to be controlled by an efficient horizontal eddy diffusion with a time scale of 30 days or shorter although the CO distribution below the clouds seems to be controlled by the meridional circulation. The pole-ward wind speed of the meridional circulation above the clouds is estimated to be 0.2 m s⁻¹ or less based on the difference between the CO mixing ratios above and below the clouds.  相似文献   

Ceno-Tethyan Jurassic Radiolarian Fauna from the Raskoh Arc, Balochistan, Pakistan     

Rehanul Haq SIDDIQUI  Takahito NAKA  Munir ul HAQ 《地球学报》2009,30(Z1):70-78

The Raskoh arc is about 250 km long, 40 km wide and trends in ENE direction. The arc is convex towards southeast and terminated by the Chaman transform fault zone towards east. This arc is designated as frontal arc of the Chagai-Raskoh arc system. The Late Cretaceous Kuchakki Volcanic Group is the most widespread and previously considered the oldest unit of the the Raskoh arc followed by sedimentary rock formations including Rakhshani Formation (Paleocene), Kharan Limestone (Early Eocene) and Nauroze Formation (Middle Eocene to Oligocene), Dalbandin Formation (Miocene to Pleistocene), and semi-unconsolidated Subrecent and Recent deposits. The Rakhshani Formation is the most widespread and well-exposed unit of the Raskoh arc. During the present field investigation the Rakhshani forma-tion in the southeastern part of the Raskoh arc, is identified as an accretionary complex, which is designated as Raskoh accretionary complex. The Raskoh accretionary comple is subdivided into three units: (a) Bunap sedimen-tary complex, (b) Charkohan radiolarian chert, and (c) Raskoh ophiolite melange. The Bunap sedimentary complex is farther divided into three tectonostratigraphic units viz., northern, middle and southern. Each unit is bounded by thrust faults, which is usually marked by sheared serpentinites, except northern unit, which has gradational and at places faulted contact with the Kuchakki Volcanic Group. The northern unit is mainly composed of allochthonous fragments and blocks of limestone, sandstone, mudstone and the volcanics in dark gray, greenish gray and bluish gray siliceous flaky shale. At places the shale is metamorphosed into phyllite. This unit is thrust over the middle unit, which exhibits relatively a coherent stratigraphy, represented by greenish gray calcareous flaky shale with intercalation of thin beds and lenticular bodies of mudstone, sandstone and limestone. The middle unit is again thrust over the southern unit, which is mainly composed of large exotic blocks of volcanic rocks, limestone, sand-stone, mudstone and conglomerate embedded in dark gray, greenish gray and bluish gray siliceous flaky shale which is generally moderately argillized. The unit is thrust over the Kharan Limestone. During the present field investigation about 350 meter thick sequence of thin-bedded maroon and green chert intercalated with the siliceous flaky shale of the same colour are discovered within this unit, which is found in the southeastern part of the Ras-koh arc. This chert sequence occurs on the margins of a large exotic block (350m X 3 km) of volcaniclastic rocks of unknown origin, which makes an overturned syncline. This chert sequence is developed on its both limbs and has lower faulted contact with the Bunap sedimentary complex. Two samples collected from this chert sequence yielded radiolarian fauna, which include Parvicingula sp., Laxto-rum sp., Parahsuum cf. simplum, Parahsuum sp., Nassellaria gen. et sp. indet., Hsuum cf. Matsuokai., Archaeo-spongoprunum sp., Nassellaria gen. et sp. indet. and Hagias gen. et sp. indet., Tricolocapsa sp., Hsuum sp., Ris-tola sp., Archaeospongoprunum sp. and Tritrabinate gen. et sp. indet. This radiolarian chert sequence represents the late Early to Middle Jurassic pelagic sediment deposited in Ceno-Tethyan ocean floor; prior to the inception of volcanism in the Raskoh arc and accreted with the arc during Late Cretaceous to Eocene along with the Bunap sedimentary complex of Late Jurassic age.  相似文献   

3-D Simulation of Earthquake Generation Cycles and Evolution of Fault Constitutitve Properties     

C. Hashimoto  M. Matsu'ura 《Pure and Applied Geophysics》2002,159(10):2175-2199

--The earthquake generation cycle consists of tectonic loading, quasi-static rupture nucleation, dynamic rupture propagation and stop, and subsequent stress redistribution and fault restrengthening. From a macroscopic point of view, the entire process of earthquake generation cycles should be consistently described by a coupled nonlinear system of a slip-response function, a fault constitutive law and a driving force. On the basis of such a general idea, we constructed a realistic 3-D simulation model for earthquake generation cycles at a transcurrent plate boundary by combining the viscoelastic slip-response function derived for a two-layered elastic-viscoelastic structure model, the slip- and time-dependent fault constitutive law that has an inherent mechanism of fault restrengthening, and the steady relative plate motion as a driving force into a single closed system. With this model we numerically simulated the earthquake generation cycles repeated in a seismogenic region on a plate interface, and examined space-time changes in shear stress, slip deficits and fault constitutive properties during one complete cycle in detail. The occurrence of unstable dynamic slip brings about decrease both in fault strength and shear stress to a constant residual level. After the arrest of dynamic slip, the breakdown strength drop j†_p of fault is restored rapidly and the process of stress accumulation resumes in the seismogenic region. On the other hand, the restoration of the critical weakening displacement D_c proceeds gradually with time through the interseismic period. The restoration of D_c can be regarded as the macroscopic manifestation of the microscopic recovery process of fractal fault surface structure. Through numerical simulation with a multi-segmented fault model, we examined the effects of viscoelastic fault-to-fault interaction. The effect of transient viscoelastic stress transfer through the asthenosphere is significant as well as the direct effect of elastic stress transfer, and it possibly explains the time lag of the sequential occurrence of large events along a plate boundary.  相似文献   

Evaporation metamorphism of primitive dust material in the early solar nebula     

Akihiko Hashimoto  Mineo Kumazawa  Naoki Onuma 《Earth and Planetary Science Letters》1979,43(1):13-21

An evaporation experiment on matrix material of the Murchison (C2) meteorite up to 1900°C in vacuo has revealed the evaporation sequence of primitive dust material and the associated evolution of residual solid phases from hydrous silicates through magnesium silicates and iron-metal to calcium-aluminum oxides. The comparison with primitive meteorites suggests that the evaporation metamorphism coupled with the re-condensation may have played an important role in the generation of diverse primitive meteorites in the early solar nebula.  相似文献   

A note on stilpnomelane mineralogy     

Mitsuo Hashimoto 《Contributions to Mineralogy and Petrology》1969,23(1):86-88

Stilpnomelane analyses are classified into two separate groups of ferro- and ferristilpnomelanes on the H₂O(+)-Fe₂O₃/(Fe₂O₃+FeO) diagram. The relation is not comparable with that of oxyhornblende.  相似文献   

Robust active vibration suppression control with constraint on the control signal: application to flexible structures     

A. Forrai  S. Hashimoto  H. Funato  K. Kamiyama 《地震工程与结构动力学》2003,32(11):1655-1676

A unified mathematical framework, sustained by experimental results, is presented for robust controller design taking into account the constraint on the control signal. The design procedure is exemplified for an active vibration suppression control problem with applications to flexible structures. The considered experimental set‐up is a three‐storey flexible structure with an active mass driver placed on the last storey. First, the considered flexible structure is identified and the model's parametric uncertainties are deduced. Next, control constraints are presented for the robust control design problem, taking into account the restriction imposed on the control signal. Finally, the effectiveness of the control system is tested through experiments, when the input disturbance is assumed to be a sinusoidal one as well as a historical earthquake record (1940 El Centro record). Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Variation of the distribution coefficients of rare earth elements in modern coral-lattices: species and site dependencies     

T Akagi  Y Hashimoto  H Tsuno  Y Nakano 《Geochimica et cosmochimica acta》2004,68(10):2265-2273

Rare earth element (REE) concentrations in the carbonate lattice of four species of coral have been analyzed and compared with the dissolved REE in ambient seawaters. The corals were from two areas of different salinity, marine (34-34.5) and bay (33-34). The measurement of REE in coral was carried out with inductively coupled plasma mass spectrometry (ICP-MS) after meticulous washing of coral samples, digestion with acetic acid and preconcentration of REE. The concentrations of REE in the two ambient seawaters were quite different, being ten-times higher in the bay area and enriched in light REE. However, the average distribution coefficients (D’s) were almost identical in the two areas. Substantial distribution coefficient differences were observed among the four coral species and the magnitude of inter-species variation in D was also species-dependent. Theoretical calculations imply that pH variation could cause variations in D large enough to account for the small differences between the two areas.  相似文献   

3-D Modelling of Plate Interfaces and Numerical Simulation of Long-term Crustal Deformation in and around Japan     

Chihiro Hashimoto  Kenji Fukui  Mitsuhiro Matsu’ura 《Pure and Applied Geophysics》2004,161(9-10):2053-2068

— We developed a 3-D simulation model for long-term crustal deformation due to steady plate subduction in and around Japan by incorporating viscoelastic slip-response functions into a realistic 3-D plate interface model, constructed on the basis of the topography of ocean floors and hypocenter distributions of earthquakes. The lithosphere-asthenosphere system is modelled by an elastic surface layer overlying a Maxwellian viscoelastic half-space. Kinematic interaction at plate interfaces is rationally represented by the increase of tangential displacement discontinuity (fault slip) across the interfaces. With this model, giving the steady slip rates at plate interfaces calculated from NUVEL-1A, we simulated long-term crustal deformation due to steady plate subduction in and around Japan. The simulated crustal deformation pattern is characterized by steep uplift at island arcs, sharp subsidence at ocean trenches and gentle uplift at outer rises. The numerical results show the strong dependence of the deformation pattern on the 3-D geometry of plate interfaces.  相似文献   

The characterization and distribution of aerosol and gaseous species in the winter monsoon over the western pacific ocean     

T. Okita  M. Okuda  K. Murano  T. Itoh  I. Kanazawa  M. Hirota  H. Hara  Y. Hashimoto  S. Tsunogai  S. Ohta  Y. Ikebe 《Journal of Atmospheric Chemistry》1986,4(3):343-358

During the winters of 1981 and 1982, measurements were taken on two Japanese islands of the aerosol and gaseous species which had been carried by northwesterly monsoons over the Pacific Ocean. The aerosols were characterized as sea-salt particles; soil particles, and as particles of sulfate, nitrate, organics and elemental carbon. At Chichi-jima island, which is about 800 km away from the main islands of Japan, it was found that the level of the anthropogenic components of the aerosols was considerably higher than their background level. The mean concentrations of the species on the islands are given in tabular forms. According to a survey made on board a ferry boat, the aerosol and gaseous species were fairly uniformly distributed along the southern coast of the main Japanese islands.  相似文献