On the 3/1 planar and circular resonant problem     

Tadashi Yokoyama  Massae Sato 《Celestial Mechanics and Dynamical Astronomy》1986,39(2):117-132

The simplest model of a resonant problem of second order is the planar and circular case. Simplification like this is very old and for 3/1 resonance, several authors have studied this problem with different purposes. In this work, we test this model for the available asteroids, by applying Hori's perturbation method. Explicit solutions of the intermediate orbit are obtained. In the plane of two constants of the problem, all types of motion are described. By testing the model, it is shown that, in general, one can confirm results of numerical integrations indicating libration for a few number of asteroids and circulation for most of them. However, agreement in numerical values for amplitude and period of librations seems to be not possible mainly if Jupiter's eccentricity is neglected. On the other hand, even though there might be some physical reasons determining that only asteroids with high eccentricity may librate, it is shown that, from mathematical point of view, libration may occur even in the case of small eccentricities provided that some relations are satisfied.  相似文献   

Age of glacial and periglacial landforms in northern Hokkaido, Japan, using OSL dating of fine grain quartz     

R. Kondo  S. Tsukamoto  H. Tachibana  Y. Miyairi  Y. Yokoyama 《Quaternary Geochronology》2007,2(1-4):260-265

The timing of glacial advances, periglacial phenomena, and the ages of two marker tephras in northern Hokkaido were estimated by OSL dating. It appears that the glacier of Yamunai 2 stage on Rishiri Island expanded between 24 and 15 ka. In northern Hokkaido, OSL ages indicate ice wedge formation during the period 24–18 ka. These results indicate that both the glacial advance and the development of ice wedges were synchronous phenomena relating to the Last Glacial Maximum.  相似文献   

Magma eruption rates of Merapi volcano,Central Java,Indonesia during one century (1890–1992)     

Suparto Siswowidjoyo  Ismangun Suryo  Izumi Yokoyama 《Bulletin of Volcanology》1995,57(2):111-116

The magma eruption rates of Merapi volcano form 1890 to 1992 are re-examined chronologically. For this volcano, movements of extruded lavas and domes as well as their extrusions are important because they control the modes of the subsequent activities and cause nuées ardentes and lahars. The monthly eruption rates varied widely, but the cumulative volume of lavas has increased linearly and is expressed as 0.1x10⁶ m³/month. The magma production rate of this volcano may have been constant for these 100 years. Recurrent excessive effusion of lavas is tentatively interpreted by assuming a magma reservoir. The averaged eruption rate is small in comparison with other volcanoes such as Nyramuragia, Kilauea and Vesuvio. However, it is remarkable that the activity has been continuous for these 100 years and the total amount of lava discharged during this period reached more than 10⁸ m³. A simple model for the formation of the 1992 lava dome is presented. The viscosity of the lavas is probably between 10⁶ and 10⁷ P and the length of the magma conduit is probably less than 10 km.  相似文献   

Verification of two-dimensional non-linear analysis of sand-structure system by examining the results of the shaking-table test     

Akira Ohtsuki  Masanori Hirota  Kikuo Ishimura  Kazutomo Yokoyama  Kiyoshi Fukutake 《地震工程与结构动力学》1992,21(7):591-607

The verification of a two-dimensional non-linear analysis based on a hybrid constitutive model, which consists of the Ramberg-Osgood model extended to two-dimensional problems and a dilatancy model, is discussed through a comparison of the shaking-table test results for a one-storey structure standing on a dry sandy deposit with those for the same on a saturated sandy deposit. Since the relationships G vs. γ and h vs. γ for shear strains of 10^?5?10^?3 can be obtained accurately by an inversion analysis of the resonance curve of the sandy deposit the proposed non-linear method can represent well the observed non-linear response of the dry or the saturated sandy deposit including the structure. This method, however, should be applied carefully to assess the response of a soil-structure system when the three-dimensional interaction affects significantly the response of the model. An equivalent linear analysis using a sway-rocking model is applied to simulate the non-linear ground motion including the three-dimensional interaction, and it is found that the sway-rocking model can also represent well the non-linear response of the system.  相似文献   

Precursory earthquakes of the 1943 eruption of Paricutin volcano, Michoacan, Mexico     

I. Yokoyama  S. de la Cruz-Reyna 《Journal of Volcanology and Geothermal Research》1990,44(3-4)

Paricutin volcano is a monogenetic volcano whose birth and growth were observed by modern volcanological techniques. At the time of its birth in 1943, the seismic activity in central Mexico was mainly recorded by the Wiechert seismographs at the Tacubaya seismic station in Mexico City about 320 km east of the volcano area. In this paper we aim to find any characteristics of precursory earthquakes of the monogenetic eruption. Though there are limits in the available information, such as imprecise location of hypocenters and lack of earthquake data with magnitudes under 3.0.The available data show that the first precursory earthquake occurred on January 7, 1943, with a magnitude of 4.4. Subsequently, 21 earthquakes ranging from 3.2 to 4.5 in magnitude occurred before the outbreak of the eruption on February 20. The (S - P) durations of the precursory earthquakes do not show any systematic changes within the observational errors. The hypocenters were rather shallow and did not migrate.The precursory earthquakes had a characteristic tectonic signature, which was retained through the whole period of activity. However, the spectra of the P-waves of the Paricutin earthquakes show minor differences from those of tectonic earthquakes. This fact helped in the identification of Paricutin earthquakes. Except for the first shock, the maximum earthquake magnitudes show an increasing tendency with time towards the outbreak. The total seismic energy released by the precursory earthquakes amounted to 2 × 10¹⁹ ergs. Considering that statistically there is a threshold of cumulative seismic energy release (10^17–18ergs) by precursory earthquakes in polygenetic volcanoes erupting after long quiescence, the above cumulative energy is exceptionally large. This suggests that a monogenetic volcano may need much more energy to clear the way of magma passage to the earth surface than a polygenetic one.The magma ascent before the outbreak of Paricutin volcano is interpretable by a model of magma-filled crack formation proposed by Weertman, based on seismic data and other field observations.  相似文献   

Seismic energy releases from volcanoes     

Izumi Yokoyama 《Bulletin of Volcanology》1988,50(1):1-13

Seismic energy release during the precursory, eruptive and declining stages of volcanic activities provides various information about the mechanisms of volcanic eruptions and the temporary developments of their activities. Hitherto the energy release patterns from precursory earthquake swarms were used to predict the eruption times, especially of andesitic or dacitic volcanoes. In this paper the discussion is expanded to quantify the total amount of seismic energy released at the threshold of volcanic eruptions, with reference to the results observed at several volcanoes. The results generally indicate that the cumulative seismic energy release from the precursory earthquake swarms exceed 10¹⁷¹⁸ergs before eruptions at any andesitic or dacitic volvanoes. This allows the seismic efficiency, or the ratio of energy radiated seismically, and the energy required for the volumetric expansion to be estimated by incorporating available deformation data with the seismic data. The dependency of seismic efficiency on the type of volcanic activity, i. e. non-explosive outbreaks, phreatic and magmatic eruptions, dome formation, etc., was evaluated from observations at a few volcanoes that provided a variety of examples.  相似文献   

Formation of intermediate-mass black holes as primordial black holes in the inflationary cosmology with running spectral index     

Toshihiro Kawaguchi  Masahiro Kawasaki    Tsutomu Takayama  Masahide Yamaguchi  Jun'ichi Yokoyama 《Monthly notices of the Royal Astronomical Society》2008,388(3):1426-1432

Formation of primordial black holes (PBHs) on astrophysical mass scales is a natural consequence of inflationary cosmology, if the primordial perturbation spectrum has a large and negative running of the spectral index as observationally suggested today because double inflation is required to explain it and fluctuations on some astrophysical scales are enhanced in the field-oscillation regime in between. It is argued that PBHs thus produced can serve as intermediate-mass black holes (IMBHs), which act as the observed ultraluminous X-ray sources (ULXs) by choosing appropriate values of the model parameters in their natural ranges. Our scenario can be observationally tested in near future because the mass of PBHs is uniquely determined once we specify the values of the amplitude of the curvature perturbation, spectral index and its running on large scales.  相似文献   

Reappearance of ordered motions in strongly nonlinear Hamiltonian systems     

Tadashi Yokoyama 《Celestial Mechanics and Dynamical Astronomy》1984,33(2):99-109

A strongly nonlinear Hamiltonian system which occurs in Celestial Mechanics is studied by the method of surface of section. The reappearance of ordered motions is observed and the numerical experiments suggest that this phenomenon could be predicted by the criterion of interaction of resonances.  相似文献   

Weathering profile of non-welded ignimbrite and the water infiltration behavior within it in relation to the generation of shallow landslides   总被引：1，自引：0，他引：1  

Masahiro Chigira  Osamu Yokoyama 《Engineering Geology》2005,78(3-4):187-207

The mechanism underlying rain-induced shallow landslides of non-welded ignimbrite is found to be a special type of weathering profile and the behavior of water infiltrating through that profile, according to our study of Ito ignimbrite in southern Kyushu, Japan. Rhyolitic volcanic glass, the primary component of ignimbrite, is first hydrated and dissolved, forming halloysite. Halloysite near ground surface is then transported through the ignimbrite by infiltrating water and becomes clogged in interstices to form clay bands. Suction monitoring across a weathering profile indicated that downward infiltration of water is disrupted once by a zone of less-permeable clay bands and again at the weathering front. This disruption at the front is caused by a capillary barrier effect caused by the structure where finer, weathered material overlies coarser, fresh material. This results in a well-defined weathering front, particularly beneath a slope where water flux is parallel to the front, whereas the front is transitional beneath a ridge top where the front is nearly horizontal and the water flux is normal to the front. Infiltrating water from rain increases the weight of weathered material and decreases the suction within the material, which is the final trigger of a shallow landslide of non-welded ignimbrite; long-term weathering, which proceeds on the order of years, provides slide material.  相似文献   

Monazite age spectra in the Late Cenozoic strata of the Changjiang delta and its implication on the Changjiang run-through time   总被引：6，自引：0，他引：6  

Yokoyama Kazumi 《中国科学D辑(英文版)》2005,48(10)

Uplift of the Tibetan Plateau, inversion of eastern and western geomorphology, eastward flowing of large rivers, and run-through of the Changjiang River exert great influence on sedimentation and environ-mental variations in the East China Sea. Provenance discrimination of Tibetan-Plateau-originated sediments in the river-mouth areas and marginal seas is key to figure out these issues.In the past, most studies of the run-through time of the Changjiang and the Yellow rivers focused on geomo…  相似文献