巻号一覧
46 巻 (1993 - 1994)
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前身誌
46 巻, 3 号
選択された号の論文の13件中1～13を表示しています
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梶川 昌三, 山田 功夫, 深尾 良夫1993 年 46 巻 3 号 p. 229-235
発行日: 1993/12/14
公開日: 2010/03/11
ジャーナル フリーOne of the largest different conditions between the nature and laboratory experiment of rock fracturing is strain rate. Conventional experiment at a constant strain rate may not simulate the precursory stage of seismic fracture, where strain rate is so low that any anomalous crustal deformation may occur by consuming the strain energy that has already accumulated rather than one newly supplied from the exterior. In order to simulate such a preseismic stage of the crust, we conducted a “zero strain-rate experiment” using Westary granite as a sample. The granite specimen is loaded at a constant strain-rate mode until stress reaches a level about 90% of the fracture stress. The bulk axial strainis then kept constant by servo-control to observe the time-variations of axial stress, local strains, dilatant strain and AE-activity.
Initially the axial stress decays exponentially and then linearly until the sample is finally broken. Axial surface strain shows a different behavior at different locality; strain concentration occurs in the area near the final fault and strain relaxation in the area far from it. Very anomalous behaviors are observed in both the areas just prior to the final break. Some implications of these results are discussed in conjunction with the field observations of crustal deformation before earthquake occurrence.抄録全体を表示PDF形式でダウンロード (860K) -
(I) 重力異常陰影図の作成工藤 健, 河野 芳輝1993 年 46 巻 3 号 p. 237-243
発行日: 1993/12/14
公開日: 2010/03/11
ジャーナル フリーUndulations of gravity anomalies are caused by horizontal and vertical variation of subsurface density. Distributions of gravity anomalies have been generally presented by contouring. Contouring method, however, is not suitable for representing fine undulations in such case that their amplitudes are less than a contour interval. For the purpose to display detailed gravity anomaly undulations, we employed a shaded relief map method and applied to gravity datasets of the Japanese Islands.
In order to extract gravity anomalies due to crustal structures, contribution due to subducting plates was subtracted from observed ones. The contribution was calculated by using a 3D subducting plate model. We call the resultant gravity anomalies as Slab Residual Bouguer Anomalies (SRBA) here. By using SRBA datasets, shaded relief maps were generated.
These shaded relief gravity anomaly maps indicate detailed variations in gravity anomalies like satellite images. In the maps we can recognize many lineament-like patterns. Although some of them correspond to known geologic faults, many of them do not. These patterns presumably indicate the existence of “hidden” faults which are covered by Quaternary sediments or volcanic products.
Descriptions of characteristic patterns which appeared on the shading relief maps and their geological and geophysical implications will be discussed in the next paper.抄録全体を表示PDF形式でダウンロード (4155K) -
隈元 崇, 池田 安隆1993 年 46 巻 3 号 p. 245-258
発行日: 1993/12/14
公開日: 2010/03/11
ジャーナル フリーThe Kofu basin is situated in the south Fassa Magna, and is bordered on the west and south by active thrust faults. Previous studies have suggested that these faults are low angle thrust, from qualitative evidence. The activity of these faults has been evaluated in terms only of vertical slip rates, in spite of the fact that a low angle thrust fault has significant component of horizontal shortening. We attempted to determine the rates of net slip on these faults using gravity and geomorphological data. First, the geometry of the faults to 2-3km depths was determined by using closely spaced gravity values across the faults. In the Sone Hills along the south margin of the Kofu basin, the master boundary fault (presently inactive), which has thrust basement rocks northward over basin fill sediments, dips 10° south. The frontal active fault at the northern margin of the hills dips 5° south, and develops wholly within the basin fill sediments, indicating thrust-front migration. In the Ichinose Upland along the west margin of the basin, however, the boundary fault (dipping 18° west) between basement rocks and basin fill sediments lies in front of the foothills, not at the topographic range front; the active fault at the range front is likely to be a secondary or subsidiary fault. Second, the rate of net slip on these faults was determined by elastic dislocation models, using geomorphologically observed surface deformation and the fault geometry that were deduced from gravity anomaly. The net slip rates were found to be 1.3mm/yr for the Sone Hills, and as high as 6.3-8.3mm/yr for the Ichinose Upland. These results indicate that the west margin of the Kofu basin is subjected to horizontal shortening in an E-W direction at an extremely high rate, whereas the south margin of the basin is subjected to horizontal shortening in a NW-SE direction at a lower rate.抄録全体を表示PDF形式でダウンロード (1764K) -
その1. 線震源からの入射と平面波入射との比較大堀 道広, 野畑 有秀, 若松 邦夫, 安井 譲1993 年 46 巻 3 号 p. 259-267
発行日: 1993/12/14
公開日: 2010/03/11
ジャーナル フリーIn the analysis of the seismic response of sediment-filled valleys, line source and plane wave incidence are very often used to generate seismic excitations. However, it has not been verified thoroughly how strong the difference of these incident waves affects the response of such geological structures. In the present paper, we calculated the time domain responses of a shallow sediment-filled valley due to several types of incident waves (plane SH wave, line source with no radiation pattern and line source with single couple radiation pattern). The calculations are performed using two-dimensional (2-D) boundary integral equation method. After normalization of incident wave amplitude at the edge of the valley, the time domain waveform and the maximum amplitude from different incident waves are compared. Throughout the study, it has been confirmed that source location and radiation pattern greatly affect the amplitude and waveform in the first phase consisting of body wave. However, the influence of these parameters on the amplitude and waveform in the later phases (generated at the edge of valley) is very small. The amplitude and waveform from plane wave incidence agree with those from a line source even if the source is located near but off the valley or has a single couple radiation pattern. In conclusion, plane wave incidence is very useful assumption in the analysis of the seismic response of sediment-filled valleys. When compared to incidenct wave from line source, the plane wave incidence show larger amplitude as for the first phase and equal amplitude for later phases.抄録全体を表示PDF形式でダウンロード (951K) -
坂部 和夫, 山内 常生, 宮島 力雄, 奥田 隆1993 年 46 巻 3 号 p. 269-273
発行日: 1993/12/14
公開日: 2010/03/11
ジャーナル フリーSurveys of γ-ray intensity around the Fukouzu fault were carried out by automatic measuring systems with a GM-survey meter and microcomputer. The Fukouzu fault, and its secondary fault were formed at the time of the Mikawa earthquake in 1945. These are reverse faults. We selected observation sites along these faults where the crustal deformation resulting from the event is well preserved. The survey was conducted by several observation systems of γ-ray intensity on a line across the faults at intervals of 5 to 280m. The results of the survey show the following for almost all of the sites: (1) the intensity of γ-rays at the upheaval sites is greater than that of others; (2) peak γ-ray intensity is seen at the upheaval sites; and (3) as thickness of alluvion increases, peak value of intensity decreases. We concluded that radioactive elements are condensed at the upheaval sites along the faults where many fissures are produced.抄録全体を表示PDF形式でダウンロード (518K) -
川崎 慎治, 小林 芳正1993 年 46 巻 3 号 p. 275-283
発行日: 1993/12/14
公開日: 2010/03/11
ジャーナル フリーSeismic reflection survey was conducted in Yokooji, the middle of the Kyoto basin in 1992. The reason why this site was chosen is that this is just the place where UEMURA and NAKATSUKA (1992) inferred a buried fault (named Yokooji fault) from wells' data. According to them, there is a systematic sudden change in depth of the lower sand and gravel layer which is widely spread at the depth of about 10m in the middle of the Kyoto basin. They have suggested that its change was caused by a buried fault running from east to west, which is likely a sub-fault of the Arima-Takatsuki tectonic line.
Though no topographical feature is found in this area, such a buried fault can have a high activity when the movement has begun in the recent past. From the disaster prevention point of view, it is hence important to investigate the subsurface structure of the possible fault to determine its activity even in the middle of a basin. It also can provide some information of the basin's growth history which leads to a better understanding of the Quaternary tectonics.
An air gun was used as a sourse apparatus. Through the data-processing for the CDP profiling, geological information of the site was obtained as follows:
(1) A velocity model up to the basement is obtained. The depth of the basement is estimated as 400-500m.
(2) A few reflections from interfaces in the Osaka group (unconsolidated sediments above the basement) are discerned. The key layer (Ma3) at 200m-300m below the ground surface is found to be consistent with the result of existing boring surveys. Considering Ma3 is 0.9 million years old, it is estimated that the middle of the Kyoto basin has been subsiding at the rate of 0.2m-0.3m/1000 years.
(3) From the revealed shape of the interfaces in the Osaka group, neither a large fault nor a large fold is found at the very position where UEMURA and NAKATSUKA (1992) suggested a buried fault.抄録全体を表示PDF形式でダウンロード (1206K) -
古川 信雄, 大見 士朗1993 年 46 巻 3 号 p. 285-295
発行日: 1993/12/14
公開日: 2010/03/11
ジャーナル フリーA simple method to determine hypocenters of earthquakes taking account of a lateral heterogeneity of the Earth is proposed. In this method we calculate a hypocenter using station corrections as a function of hypocenter coordinates (x, y, z). The lateral heterogeneity is corrected by these station corrections. We assume that station correction SCj at a j-th station is represented as follows: SCj=aj+bjx+cjy+djz+ejxy+fjyz+gjzx+hjx2+kjy2+ljz2. Where aj, bj, …, lj are constant.
Coefficients aj, bj, …, lj are obtained as follows: Dividing a whole region into many sub-regions, we relocate earthquakes in each sub-region by the method of joint hypocenter determination. We regard station corrections obtained in this sub-region as those at the center of the sub-region. Obtaining station corrections at all sub-regions, we interporate them by a function that is a quadratic form of x, y and z. Station correction SCij at the j-th station obtained at the i-th sub-region is represented as follows: SCij=aj+bjxi+cjyi+djzi+ejxiyi+fjyizi+gjzixi+hjxi2+kjyi2+ljzi2. Where xi yi and zi are x, y and z coordinates of the center of the i-th sub-region, respectively.
Obtaining station corrections at 41 stations of the Kanto network of the National Research Institute for Earth Science and Disaster Prevention, we relocated earthquakes in the Kanto district. Since the effect of the lateral heterogeity is taken account of, there is no magnitude dependence of hypocenters, which obscures spacial distribution of earthquakes determined by the previous method. We can obtain a fine distribution map of hypocenters.抄録全体を表示PDF形式でダウンロード (1108K) -
根岸 弘明, 佐藤 魂夫1993 年 46 巻 3 号 p. 297-308
発行日: 1993/12/14
公開日: 2010/03/11
ジャーナル フリーWe analyzed amplitude and travel time fluctuations from 135 teleseismic events for 17 stations in northern part of Tohoku region, Japan. Average terms and azimuth-independent terms and first and second azimuthal-dependent terms are obtained for relative log-scaled amplitude (hereinafter referred to as log-amplitude) and relative travel time residual (hereinafter referred to as time residual). The averages for the log-amplitudes are small by the volcanic front and medium at Pacific-Ocean side, but they have no clear tendency at Japan-Sea side. This geographical variation does not correlate well with the Q-structure of the crust and upper mantle in this western region. The amplitudes tend to be affected by the local geology; larger amplitudes are obtained at the stations where the geology is young. The azimuthal terms do not show clear tendency for the amplitudes.
For the time residuals, the average terms show clear indication of early arrival for the stations at Pacific-Ocean side, and late arrival for the stations at Japan-Sea side. This geographical variation harmonizes with the velocity structure of the crust and the upper mantle beneath the station network. Azimuthal terms show different trends between western region and eastern region; the first azimuthal terms point toward opposite directions, and the second azimuthal terms intersect each other perpendicularly between each regions.
Correlations between log-amplitudes and time residuals are generally weak. Good correlations at some stations suggest the focusing and defocusing of rays by the heterogeneity beneath the station sites. The log-amplitude plotted as a function of time residual has a negative correlation for small amplitudes at late arrivals. It may represent that the focus point is not near the surface owing to the focusing by low-velocity zone at deep interiors. For the travel time, average terms show a significant correlation with gravity (Bouguer) anomalies, but for log-amplitude, it shows only weak correlation.抄録全体を表示PDF形式でダウンロード (1204K) -
木股 文昭, 中村 勝, 宮島 力雄, 奥田 隆, 里村 幹夫, 佐々木 嘉三1993 年 46 巻 3 号 p. 309-311
発行日: 1993/12/14
公開日: 2010/03/11
ジャーナル フリーPDF形式でダウンロード (372K) -
福島 美光1993 年 46 巻 3 号 p. 315-328
発行日: 1993/12/14
公開日: 2010/03/11
ジャーナル フリーRecent studies on the attenuation relations of earthquake ground motion, which have been derived mainly by multiple regression analyses of observed data, are surveyed. Since the studies on the attenuation relations are involved with not only derivation of attenuation characteristics but also evaluation of source and site effects, they have wide variety of theme. In this report, these studies are reviewed by dividing them into four aspects of the study: parameters used in regression models, observed data, regression models and methods of statistical analyses.
Main topics of recent studies are as follows. (a) Ordinary regression models that assume linear relationship with respect to magnitude will fail to represent the response spectra in wider magnitude range, since magnitude dependency of the ω-2 source spectra is not linear around corner frequencies. (b) Distance coefficients of attenuation relations obtained from the regression analyses can be converted to the Q values, which agree well to those derived by different approaches. (c) The phenomena of amplitude saturation in the near source region, which is prominent in high-frequency components of strong ground motion, can be expressed by substituting the hypocentral distance with the minimum distance to the fault plus the source region size. Another approach is to sum up the contributions from small elements located on a large fault plane. (d) Significantly smaller distance coefficients for large numbers of earthquake than for an individual earthquake will be derived by the ordinary one-step regression analysis, because usually strong correlation between magnitude and distance exists in such a large database. The two-step stratified regression analysis using dummy variables is a very effective method to correct these unreasonable results. Thus care should be taken for the choice of the regression procedures and models, especially in case that the observed data have a bias.
Since attenuation relations are derived based on observed records, the ground motion predicted by these relations will be a good approximation of the actual value as long as the model parameters for prediction fall within the range of the data for regression. In near future, the attenuation relations applicable to wider frequency, magnitude, and distance ranges are anticipated to be developed with the help of increasing strong motion data and appropriate physical modeling.抄録全体を表示PDF形式でダウンロード (1896K) -
座間 信作1993 年 46 巻 3 号 p. 329-342
発行日: 1993/12/14
公開日: 2010/03/11
ジャーナル フリーThe knowledge about strong ground motion in a long-period range, from a few to over ten seconds, has been required, because a number of large-scale structures, such as high-rise buildings, long-spanbridges, and large oil tanks, has been increasing.
In this paper, recent studies on such long-period ground motion are reviewed in the following points: (1) interpretation of observed records, (2) generation and propagation characteristics, (3) regionality, and (4) numerical modeling. Successful simulations for wave propagation show that long-period strong ground motion is mainly composed of surface waves. This suggests that long-period ground motion can be predicted when input motion and/or source parameters, and subsurface structural model are given appropriately.抄録全体を表示PDF形式でダウンロード (2083K) -
堀家 正則1993 年 46 巻 3 号 p. 343-350
発行日: 1993/12/14
公開日: 2010/03/11
ジャーナル フリーMicrotremors are extensively studied primarily in Japan to estimate conveniently seismic responses and subsurface structures of soil deposits. Methods using four quantities have been developed for this purpose; the predominant frequency, the spectral ratios between sites, the phase velocities of the surface waves, and the spectral ratios of Rayleigh waves between vertical and horizontal components. In this paper we first summarize studies of these methods and point out the problems inherent to them, and finally discuss under what conditions these techniques should be applied on the basis of the consideration of wave types contained in microtremors using elastic wave theory.抄録全体を表示PDF形式でダウンロード (1170K) -
纐纈 一起1993 年 46 巻 3 号 p. 351-370
発行日: 1993/12/14
公開日: 2010/03/11
ジャーナル フリーThe velocity structures in ‘basements’ have got important to engineering seismology from 1970's. Large-scale buildings, such as tall skyscrapers and big oil tanks, have increased, and they have so long natural periods that their seismic responses should be affected by deeper parts of underground structures than sedimentary layers. Therefore, in Japan, the seismic basement is now assumed to be the uppermost part of the crust, where the P- and S-wave velocities are around 5-6 and 3km/s, respectively.
For exploring these deep structures, a seismic refraction experiment is the most efficient and the topography of the sediment/basement interface has been revealed in the Kanto, Osaka and Nobi basins by carrying it out. The results fairly agreed with those of gravitational surveys, but a refraction experiment is not good for S-wave velocities, because the coda of P waves may overlap with S waves and it is sometimes difficult to determine their arrival times precisely.
Instead, in situ measurements at deep boreholes are more efficient if we can use an effective S-wave generator. However, since it costs much to dig a deep borehole, this measurement was carried out only at a few points in the Kanto basin. So S-wave velocities should be estimated from P-wave ones or results of other geophysical surveys, and we here note that geological knowledge is quite important for this estimation.抄録全体を表示PDF形式でダウンロード (3421K)
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