巻号一覧
47 巻 (1994 - 1995)
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前身誌
47 巻, 4 号
選択された号の論文の14件中1～14を表示しています
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体験談と地震記象の解釈武村 雅之, 池浦 友則1995 年 47 巻 4 号 p. 351-364
発行日: 1995/01/24
公開日: 2010/03/11
ジャーナル フリーSource process of the 1923 Kanto earthquake is investigated from descriptions of about 200 personal experiences near the focal region. The experiences of the strong shaking without a preliminary tremor in and around Odawara city and of the second strong vertical-shaking in the Miura Peninsula suggest that two major subevents occurred during the Kanto earthquake. We infer that the first subevent occurred under Odawara city and the second under the Miura Peninsula. The time interval between the two subevents is estimated to be about ten second from the interval between two prominent phases on an old strong-motion vertical record at Gifu observatory (Δ=226km), which was observed by a seismograph with a natural period of about 1sec. The above result of the two subevents can also explain the best documented account on the earthquake ground motion by Prof. Imamura at the Imperial University of Tokyo.抄録全体を表示PDF形式でダウンロード (2465K) -
小高 俊一, 前田 憲二1995 年 47 巻 4 号 p. 365-374
発行日: 1995/01/24
公開日: 2010/03/11
ジャーナル フリーThe space-time distribution of earthquakes which occurred for the past 68 years in the Kanto district is shown in order to look the general trend of the changes in seismic activities there. A pair of the distribution diagrams which are obtained by changing slightly the angle of projection can be used for getting 3D (three dimensional) views of hypocenter distribution (2D in horizontal plane, 1D in time). For convenience' sake, we call this as a 3.5D representation because the depths of hypocenters are also distinguished by symbols.
We can observe that seismic activities were sometimes high before the past large earthquakes which occurred in and around the Kanto area. This also happens before the 1987 Chiba-toho-oki earthquake. Detailed study reveals that seismic activities were high in and around the focal region for at least eight years before the earthquake. Further, shallow earthquakes were active there in the same period. These tendencies are more conspicuous at seismic nests which are closer to the focal region.
JMA data are used in the above analysis. Further, check is made by use of the data compiled in the Japan University Network Earthquake Catalog Hypocenters File. It reveals that some noteworthy phenomena happened in and around the focal region before the main fracturing. At about one year before the occurrence of the main shock, earthquakes in shallow depths disappeared and they concentrated in space in narrow zonal regions near where the main fracture initiated.
The 1953 Boso-oki earthquake M7.4 was also preceded by high seismicities in the wide area including the seismic nests in the Kanto area and the focal region.
We may conclude that the 1987 Chiba-toho-oki earthquake was preceded by some anomalous seismic activities in and around the focal region and we may expect that seismic nests are sensitive to changes in stress fields in surrounding areas.抄録全体を表示PDF形式でダウンロード (1390K) -
桝井 健, 武村 雅之, 釜田 正毅1995 年 47 巻 4 号 p. 375-382
発行日: 1995/01/24
公開日: 2010/03/11
ジャーナル フリーAccelerograms from the 1993 Noto-hanto-oki earthquake (MJMA=6.6) are simulated at four sites with different ground conditions by using a semi-empirical method for modeling the earthquake faulting stochastically. Seismic moment M0 and fault plane for the main shock are determined from a tsunami source model. Two element events, whose focal mechanisms are similar to that of the main shock, are selected among four large aftershocks of MJMA=5.0-5.1. Source spectra of these events follow the ω-2 model and their corner frequencies fCE are equal to or higher than those expected from the M0-fC relation by BOORE (1986). Synthesized records are in good agreement with observed ones in both cases of using these element events on the condition that standard deviations SD of displacement on the fault plane are assumed to be about five times as large as those for other large events whose source spectra follow the ω-2 model. The higher value of SD suggests that high frequency components of seismic waves were strongly excited due to some large heterogeneity of displacement on the fault plane of the main shock. This result is also supported by the fact that maximum accelerations from this event observed at stations within an epicentral distance of 200km are systematically larger than those from the 1984 Nagano-ken-seibu earthquake (MJMA=6.8), which has almost the same seismic moment as this event.抄録全体を表示PDF形式でダウンロード (906K) -
大井 昌弘, 石原 靖, 菊地 正幸, 三ヶ田 均, 渡辺 秀文1995 年 47 巻 4 号 p. 383-393
発行日: 1995/01/24
公開日: 2010/03/11
ジャーナル フリーEarthquake swarms occurred in the southeastern and southern region off the Izu-Oshima Island associated with the eruption of the volcano of Nov., 1986. We investigated the swarms using local seismic data recorded by the network of Izu-Oshima Volcano Observatory. The earthquakes are divided into three groups: group A and B along two line segments to the NW-SE direction extended from the fissure eruption; and group C along a line segment between group A and B. The focal mechanisms for 22 events are determined from the amplitude ratio of SH wave to P wave as well as the polarities of P, SH and SV waves. The results show that most earthquakes of group A and B are normal faults with the NE-SW tension axis which is perpendicular to the alignment of the epicenters, while group C are strike-slip faults. The configuration of these earthquakes indicates that the normal fault earthquakes first occurred along the two line segments and then caused the strike-slip type earthquakes between them, namely, group C earthquakes are interpreted as transform faults between the two ridge-type normal fault earthquakes.抄録全体を表示PDF形式でダウンロード (1119K) -
大野 一郎, 河野 芳輝, 藤本 博巳, 小泉 金一郎1995 年 47 巻 4 号 p. 395-401
発行日: 1995/01/24
公開日: 2010/03/11
ジャーナル フリーBoth sea surface and land gravity measurements have been carried out in and around the western Seto Inland Sea, southwestern Japan. Both kinds of data were combined to prepare a Bouguer anomaly map. The map shows that there exists in the western Seto Inland Sea a belt of intense negative gravity anomaly with a maximum of -60mgal, elongated in SW-NE direction from the east of Beppu Bay to off Matsuyama. Based on the seismic reflection profiles obtained in the east of Beppu Bay by Yusa et al. (1992), cross sections of the negative gravity anomaly belt were analyzed by Talwani's method. The results indicate the existence of a graben structure buried with low-density sediments along the negative gravity anomaly belt.抄録全体を表示PDF形式でダウンロード (814K) -
佐藤 博樹, 本多 了, 川崎 一朗1995 年 47 巻 4 号 p. 403
発行日: 1995/01/24
公開日: 2010/03/11
ジャーナル フリーPDF形式でダウンロード (135K) -
原 辰彦, ゲラー ロバート1995 年 47 巻 4 号 p. 405-409
発行日: 1995/01/24
公開日: 2010/03/11
ジャーナル フリーWe summarize recent results of our work on inversion for laterally heterogeneous earth structure using the Direct Solution Method (DSM). We obtained a 3-D upper mantle S-wave velocity model, PUM0 (Preliminary Upper Mantle model, version 0) by iterative linearized waveform inversion of surface wave data. The deep roots of ridges and cratons can be identified as the geological features responsible for the lateral heterogeneity of PUM0 at depths of 300-400km. We discuss the necessity of iterative linearized waveform inversion based on our calculations. We also discuss the future prospects for application of the DSM to waveform inversion of body wave data for the 3-D structure of the earth's deep interior.抄録全体を表示PDF形式でダウンロード (802K) -
木戸 元之1995 年 47 巻 4 号 p. 411-421
発行日: 1995/01/24
公開日: 2010/03/11
ジャーナル フリーRecent studies on global dynamics based on seismic tomographies have well explained observed long wave-length plate motion, geoid, and topography. However, only few attempts have so far been made at present-day instantaneous mantle flow because of the absence of direct observations to be compared with the large-scale flow. In this study, we calculate the three-dimensional flow pattern within the mantle using density perturbations converted from seismic tomography and imposed slabs with spherical harmonics up to degree 8. Furthermore, we extend the calculation up to degree 36 using recent high-resolution seismic tomographies and show the existence of the small-scale convection, which superimposes on the large-scale whole mantle flow, within the low-viscosity asthenosphere beneath oceans. This is consistent with admittance analyses of geoid and depth anomalies in oceans, but inconsistent with time-dependent numerical simulations, which present nearly layered convection with the exception of flushing events and have very short-wavelength hot and cold plumes.抄録全体を表示PDF形式でダウンロード (2130K) -
戸田 康史, 阿部 豊1995 年 47 巻 4 号 p. 423-429
発行日: 1995/01/24
公開日: 2010/03/11
ジャーナル フリーDAVIES (1992) suggested that plate tectonics was not operative for the early Earth, because hotter mantle produced thick, buoyant oceanic crust, which resisted subduction. We re-examine this possibility using a simple 2-D model of convection heated from within, based on the boundary layer theory. We found that a range of mantle temperatures existed in which the plate velocity decreases with increasing mantle temperature owing to the formation of thick buoyant crust, as suggested by DAVIES (1992). However, when the mantle temperature increases further still, the plate velocity again increases with increasing mantle temperature, in spite of the thick crust. This is because hot mantle produces higher density crust (such as komatiitic crust). Thus, the plate velocity and heat flux have minimum values at a certain mantle temperature, but plate motion does not stop. Hence, our result shows that the existence of an early hot mantle and the formation of thick crust does not necessarily prevent subduction. We also found that the heat flux is insensitive to changes in the mantle temperature, while it is around the minimum value.抄録全体を表示PDF形式でダウンロード (826K) -
吉田 明夫, 宝来 帰一1995 年 47 巻 4 号 p. 431-436
発行日: 1995/01/24
公開日: 2010/03/11
ジャーナル フリーVarious models for the oceanic heat flow can be grouped into three classes by the difference of thermal condition at the lower boundary of the plate. We summarize characteristics of each model paying attention to physical meaning implicitly contained in the thermal boundary conditions. On the basis of the considerations we propose a new model for the cooling of the oceanic plate which fits well to the observed data of heat flow. The essence of the model is that it takes time for the heat flow in the deep mantle to reach the surface by conduction through the solid plate. Cooling of the oceanic plate has relevance to the cooling of the deep mantle. We discuss briefly the significance of plate tectonics on the cooling of the earth.抄録全体を表示PDF形式でダウンロード (786K) -
青山 雄一, 長尾 年恭, 古本 宗充1995 年 47 巻 4 号 p. 437-441
発行日: 1995/01/24
公開日: 2010/03/11
ジャーナル フリーSince the origins of hotspots are on the core-mantle boundary, activities of hotspots are expected to be affected by activities of the core. We have analyzed the correlation between the variations of the activity of Hawaiian hotspot and the geomagnetic polarity bias. The results suggest that the activity of the Hawaiian hotspot is enhanced in the period of the normal polarity bias. The time lag of the volume flux of the hotspot volcanism behind the polarity bias is a few millions of years. The correlation and lag can be explained in terms of the development and upwelling of the plume resulting from the core fluid motions.抄録全体を表示PDF形式でダウンロード (613K) -
川嵜 智佑1995 年 47 巻 4 号 p. 443-451
発行日: 1995/01/24
公開日: 2010/03/11
ジャーナル フリーPartitioning of Ca2+, Fe2+ and Mg2+ between olivine and clinopyroxene in the CaO-FeO-MgO-SiO2 system has been thermodynamically formulated using the double-sited regular solution model for clinopyroxene and the Ca-Fe-Mg ternary regular solution model for olivine. Proposed models sufficiently describe the intracrystalline equilibrium for the exchange of Fe2+ and Mg2+ between M1 and M2 sites of clinopyroxene. The equations for the relation among the thermodynamic parameters of clinopyroxene have been derived in the extreme case that the value of the distribution coefficient of the intracrystalline exchange is equal to the unity. The models give us general solutions in the CaO-FeO-MgO-SiO2 system and approximate solutions in the case of the Ca-rich system for the distribution of Ca, Fe and Mg between olivine and clinopyroxene.抄録全体を表示PDF形式でダウンロード (1128K) -
竹下 徹, 奥平 敬元1995 年 47 巻 4 号 p. 453-467
発行日: 1995/01/24
公開日: 2010/03/11
ジャーナル フリーDynamics and thermal modeling in low-pressure/high-temperature metamorphic belts (LPMs) are reviewed. LPM found in the world is formed under such P-T conditions that the pressure is lower than that of the aluminosilicate (Al2SiO5) triple point (about 400MPa), and the peak temperature ranges between 500 and 700°C. Such anomalously high temperatures at relatively shallow depth indicate that the geothermal gradient in the upper crust exceeded 50°C km-1 at the time of LPM formation. Although the steady state geothermal gradients in the upper crust necessary for the formation of LPM could be reached by continuously supplying a huge amount of magma in the upper crust [OXBURGH and TURCOTTE (1971)], such a steady state model is unlikely because of no observation of entire melting of the lower crust which is the outcome of the steady state model. Rather, transient heat sources such as the intrusion of magma, circulation of hot fluid, subduction of young oceanic plate or spreading ridge and convective thinning of the mantle lithosphere have been proposed to be the possible heat sources for LPM. Based on the heat transfer calculations, the duration of high-temperature condition by the intrusion of magma which is several kilometer wide, is less than 1Ma, and that by the circulation of hot fluid is poorly constrained. Even in the thermal model where the highest-temperatures in the country rocks attained by the intrusion of magma are assumed to be recorded as the metamorphic temperatures, the volume of magma necessary for the formation of LPM is more than 50% of the total volume of the crust [HANSON and BARTON (1989)]. Among these thermal models of LPM, subduction of young oceanic plate or spreading ridge is a likely model of LPM, not only because there are many occurrences of LPM evolved from accretionary sedimentary piles at trench, but because the ridge subduction can cause volcanism in the forearc [e. g., DELONG et al. (1979)] in addition to the anomalous heat supply to sediments from the asthenosphere. In order to further constrain the dynamics and thermal model of LPM in future, the P-T path and the duration of low-pressure type metamorphism must be accurately estimated petrologically, and the relative timing between metamorphism and deformation must be thoroughly investigated.抄録全体を表示PDF形式でダウンロード (2295K) -
木戸 元之, 木下 肇1995 年 47 巻 4 号 p. 469-488
発行日: 1995/01/24
公開日: 2010/03/11
ジャーナル フリーSince late 1960s, many efforts have been made to elucidate the evolution of oceanic plates, based on a new concept called seafloor spreading. Several models describing the thermal state of the oceanic plate were proposed, which remain matter for debate, together with accumulation of the geophysical and geological data on seafloor. In general, observed depth and heat flow in younger seafloor are directly and inversely proportional to the square root of plate age, respectively, which is well expected by the half-space cooling model. For older seafloor, they merge into constant values asymptotically (flattening), implying the applicability of the plate model of a constant plate thickness. Numerical simulations on lithosphere-asthenosphere interaction have also been performed, depending strongly on the parameters of mantle properties and boundary conditions. A question is raised why the seafloor depth flattens in older age. To explain this flattening, a few workers advocate dynamically supported topography due to convectioe flow and/or density anomalies in the mantle; others interpret it as rejuvenation of the plate by reheating at hot spots, or as excess heat supply by small-scale convection in the asthenosphere. The former hypothesis predicts continuous thickening of the plate with age; on the contrary, the latter requires rather flat plate thickness for older age. Other geophysical observations to define the plate thickness (e. g., seismic phase velocity anomalies, geoid offset at fracture zones, etc.) do not necessarily show consistent results to each other, and some data cannot distinguish the difference between two models due to the poor resolution. We need detailed and careful surveys of oceanic plates, especially at great age, as well as numerical simulations incorporating more realistic mantle properties and thermal structure in the mantle to obtain further knowledge on the evolution of oceanic plates.抄録全体を表示PDF形式でダウンロード (3208K)
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