巻号一覧
40 巻 (1987)
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前身誌
40 巻, 3 号
選択された号の論文の15件中1～15を表示しています
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石田 毅, 金川 忠1987 年 40 巻 3 号 p. 329-339
発行日: 1987/09/25
公開日: 2010/03/11
ジャーナル フリーStress relief method has been often adopted to measure the in-situ stress state, and in this method various types of gauge have been used. If different types of gauge are used, different results can be expected. Moreover, stress distribution in an inhomogeneous rock mass is probably not uniform. Although these problems remain, they have not been clearly elucidated with in-situ data. In this study, the results measured in the same site with both hollow inclusion gauges and doorstopper-type 8-element gauges are compared. Consequently, it is shown that both results indicate the same tendency of a horizontally uniaxial compressive stress state. However, there are some differences in the magnitudes of the stresses between the two methods of measurement. Furthermore, upon examining the data obtained in this site in detail and referring to the data of two other sites, the effect of the inhomogeneity in a rock mass is discussed. As a result, it is concluded that the magnitude of in-situ stress in hard intact rock is larger than that in soft weathered rock and the dnfference between them is from 2 to 4MPa.抄録全体を表示PDF形式でダウンロード (1156K) -
木股 文昭, 中村 勝, 宮島 力雄, 奥田 隆, 藤井 巖, 青木 治三1987 年 40 巻 3 号 p. 341-347
発行日: 1987/09/25
公開日: 2010/03/11
ジャーナル フリーThe precise leveling on a small-aperture leveling net at Yake-dake volcano has been repeated almost every autumn since 1977. The net consists of ten bench marks with a total length of 520m. Geodetic tilt vectors, each calculated from elevation changes at three neighboring bench marks, are grouped on the basis of directions and sizes of vectors. Tilt vectors calculated from northeastern bench marks of the leveling net show a dip of about 1200μ rad towards north, and the others calculated from southwestern bench marks show 200μ rad dipping northwards at an average. The two geodetic tilt vectors suggest a relative upheaval of the summit on Yake-dake volcano since 1977.抄録全体を表示PDF形式でダウンロード (700K) -
日本海中部地震の最大余震 (1983年6月21日) に伴う津波阿部 邦昭1987 年 40 巻 3 号 p. 349-363
発行日: 1987/09/25
公開日: 2010/03/11
ジャーナル フリーSource area of a small tsunami, caused by the largest aftershock (June 21, 1983) of the Japan Sea Earthquake (May 26, 1983), was redetermined by refraction diagram method and was shown to be located on the south west slope of Oshima Ojima Island. It is ascertained that the source area does not conflict in location with the area of aftershocks following the largest aftershock. Some fault models were assumed to explain the tsunami source. On these models numerical experiments were carried out and the computed waveforms were compared with observed waveforms. As a result of the comparison it is shown that one of the models, which has a fault plane corresponding with the aftershock area, is harmonious with the observed tsunami waves.
The characteristic features of the tsunami were revealed in comparison with the large tsunami of the Japan Sea Earthquake. The high frequency predominance (0.0021-0.0026Hz) is attributed to a small size of the source area and a moderate sea depth in the source, and is reflected on a rapid decrease of amplitude in time history observed at the nearest station to the source.抄録全体を表示PDF形式でダウンロード (1694K) -
福島 毅, 末次 大輔, 中西 一郎1987 年 40 巻 3 号 p. 365-375
発行日: 1987/09/25
公開日: 2010/03/11
ジャーナル フリーThe possibility of moment tensor inversion for rapid prediction of tsunami height is studied. Numerical experiments of the inversion are made on a hypothetical network of digital seismograms with a very broad band and wide dynamic range. Using the normal mode theory, we invert waveforms with a duration of 3 minutes after the earthquake origin time. The experiments suggest that the rapid determination of seismic moment and source mechanism may be possible for earthquakes near Japan, if we can gather the data by a real time on-line system from several Japanese stations. The assumption of the point source in our inversion method may become invalid for great earthquakes. To estimate the effect of the source finiteness, we invert seismograms calculated for moving sources and find that the obtained scalar moment is underestimated to be half the true one for a fault length of 200km. Further studies on the inversion for finite sources are required to achieve a practical estimation of tsunami height.抄録全体を表示PDF形式でダウンロード (967K) -
加藤 祐三1987 年 40 巻 3 号 p. 377-381
発行日: 1987/09/25
公開日: 2010/03/11
ジャーナル フリーIn Ishigaki Island, the southern Ryukyu Islands, there are many blocks consist of coral limestone. These are considered to be thrown onto the island by Yaeyama Seismic Tsunami in 1771 and so called “tsunami-ishi (means tsunami-stone)”. Based on a distribution of these tsunami-ishi, a record, in archives, saying that the run-up height of the tsunami was 85 meters has been admitted. Or according to the maximum height of the distribution, an assertion that the run-up height is 55 meters has been made.
There are two kinds of blocks for these tsunami-ishi. One is genuine tsunami-ishi which is evidently thrown on the island by the tsunami. The other consists of the Pleistocene Ryukyu Limestone block. It cannot be determined whether the existence of these blocks is a result of the tsunami, or not. These coral blocks can be distinguished from each other by its components, either aragonite or calcite. That is to say, when the coral of a block consists of aragonite, it should be a genuine tsunami-ishi. When calcite, it should be a Ryukyu Limestone block. Since the research, made by this method, found out that the maximum height of the distribution of the genuine tsunami-ishi was 25 meters, it is inferred that the run-up height was a little higher than 25 meters.
In Miyara Bay of Ishigaki, there is also a block about 100 tons in weight clung by some small coral whose 14C-age corresponds with that of Yaeyama Seismic Tsunami. The 14C-age of this block itself is 2980BP. This suggests that, between at least 3000 years ago and 1771 of Yaeyama Seismic Tsunami, there was no such huge tsunami which could have thrown this large block at Miyara coast. Since, among the genuine tsunami-ishi, the 14C-age of coral of a block, distributing at the altitude of 25 meters, which is the highest altitude for this particular block, is 1810BP, this block is inferred to have been thrown by the tsunami and the value of a little higher than 25 meters is considered to indicate the maximum height of Yaeyama Seismic Tsunami.抄録全体を表示PDF形式でダウンロード (474K) -
(1) 中国華北から日本海溝へいたる地域趙 志新, 松村 一男, 尾池 和夫, 石川 有三1987 年 40 巻 3 号 p. 383-396
発行日: 1987/09/25
公開日: 2010/03/11
ジャーナル フリーMutual relations of seismicity in the long period in various regions from North China to Japan trench in East Asia have been analyzed. Time series of events were analyzed in various regions in North China, Korean Peninsula and Japan Island.
The seismicity of each region was high in the period from 1550 to 1700. Then quiet period had been lasting until 1900. From 1900 the active period began again and have continued up to the present.
Impulsive activities were found in the western part of North China and Japan Islalds in a short time range around 1830 during the quiet period. It seems that short period variations superpose on the long period variation. These short period variations in two regions also correlated to each other.
Synchronous variations of seismicity in these regions are implicated in the formation of earthquake generating stress fields from North China to Japan trench under the common tectonic conditions. The release and the accumulation of stresses correspond to the active and quiet period of seismicity, respectively.
Correlations among seismicities and stress fields from North China to Japan trench suggest that there is a transmission of the tectonic force from the subduction of the pacific plate along the Japan trench to North China through Korean Peninsula.抄録全体を表示PDF形式でダウンロード (1483K) -
小山 順二1987 年 40 巻 3 号 p. 397-404
発行日: 1987/09/25
公開日: 2010/03/11
ジャーナル フリーHeuristic approach is made to derive the seismic directivity for short-waves. Since seismic wavelengths for engineering concerns are very short, such waves are inevitable to be distorted due to heterogeneities near the source region. The excitation of the short-waves is also controlled by the small-scale fault irregularities such as fault patches, asperities and harriers.
Unilateral rupture along fault length L is considered. Fault patches are uniformly distributed on the fault with a number density of m per unit area. Since the fracture of fault patches is assumed to be random, the energy of short-waves would be additive. The maximum amplitude of short-waves is, therefore, expected to be amax=[mL2r2/Td]1/2F(K) where r2is a narrow-band average energy from one fault patch and Td is rupture time over fault length L as Td=L/c[c/v-cosθ] K corresponds to the number of peaks and troughs of the wave train considered, mL2, and F(K)=[lnK2/2π-lnlnK2/2π]1/2 The theory predicts seismic directivity for short-wave amplitudes as (c/v-cosθ)-1/2 whereas (c/v-cosθ)-1 is known for long-waves. Our previous result suggests that r2 is related to L, so that amax would increase in proportion to L.抄録全体を表示PDF形式でダウンロード (724K) -
小山 順二1987 年 40 巻 3 号 p. 405-416
発行日: 1987/09/25
公開日: 2010/03/11
ジャーナル フリーA large complex earthquake is modeled as a series of multiple point sources. This is to evaluate the time-dependent moment-tensors of complex earthquakes in a subjective manner using the least-squares criterion. Since the earthquake sources are no longer a point, low pass filterting is applied to both synthetic and observed seismograms before the inversion in order to permit a multiple point-source representation. Numerical tests of inversion schemes and least-squares programings have been done by assuming theoretically the time dependent moment tensors. It is shown that the convergence of the solutions is usually achieved within two to three iterations to the assumed moment tensors.
The theory is applied to the 1983 Japan Sea earthquake. Total seismic moment of 5.4×1027dyne·cm is obtained. The value is consistent with previous estimates from body-waves, surface-waves and tsunamis. It is revealed that the focal mechanism of the earthquake is time-changing. The focal mechanism solution as a function of time is consistent with the inferred fault plane configurations from aftershocks. A low-pass filtered focal-mechanism thus obtained would represent the mechanism for large scale fault segments. Since much more freedom is expected for the mechanisms of small scale fault patches, the mechanism must be highly at random. Such the fault patches are responsible for the short-period excitation of seismic waves due to large earthquakes.抄録全体を表示PDF形式でダウンロード (1197K) -
長宗 留男1987 年 40 巻 3 号 p. 417-423
発行日: 1987/09/25
公開日: 2010/03/11
ジャーナル フリーThe minute investigation of the spatial distribution of intermediate-depth earthquakes reveals that the deep earthquake zone beneath the Kyushu-Ryukyu region is dislocated transversely and changes its strike under the Tokara Channel.
Left-lateral dislocations of the isobaths of intermediate-depth earthquakes amount to 70-80km and 30-40km at depths of 80km and 150km, respectively. The isobath of the depth of 200km, however, is scarcely dislocated. The change in strike of the deep earthquake zone comes up to about 30° there.
The discontinuity of the zone appears to be related closely to the surface geology. The Tokara Channel represents the left-lateral geological fault offsetting by 80-100km the tectonic belts in the pre-Miocene basement rocks running parallel to the island arc. In this region, there are a few left-lateral faults including the Tokara Channel, which traverse the Ryukyu Islands and divide the pre-Miocene tectonic belts into segments of 200 to 400km in strike length. But the other transverse discontinuities of the deep earthquake zone corresponding to the surface geological structure can not be found from the present analyses.抄録全体を表示PDF形式でダウンロード (718K) -
渡辺 偉夫1987 年 40 巻 3 号 p. 425-433
発行日: 1987/09/25
公開日: 2010/03/11
ジャーナル フリーAuthor's paper (1985) shows that there is a close relationship between tsunami occurrence and tectonics off the coast of Japan. This paper studies the same problem, especially the relationship between tsunami occurrence and earthquake mechanism, on the 1983 Nihonkai-Chubu earthquake. The 1983 tsunami has many and very accurate records adding to the Korean and U. S. S. R. stations. The obtained results are followings.
1) The northern and southern boundaries of the tsunami source are parallel to the isodepth lines of the ocean bottom.
2) The apparently elongated direction of the tsunami source is the N-S direction parallel to the strike of the earthquake fault.
3) The initial amplitude of the tsunami is large at the north and south directions of the earthquake fault. The fault model derived from the aftershock area and so on shows reverse faulting on an eastward dipping plane, however, judging from the distribution of the initial amplitude of the tsunamis and so on, a possibility of the faulting on a westward dipping plane has not to be neglected.抄録全体を表示PDF形式でダウンロード (931K) -
佐藤 魂夫, 小菅 正裕1987 年 40 巻 3 号 p. 435-444
発行日: 1987/09/25
公開日: 2010/03/11
ジャーナル フリーThe Pn velocity just beneath the source area of the 1983 Japan Sea earthquake was investigated using arrival times of aftershocks of the Japan Sea earthquake observed at two stations, Matsushiro (MAT) and Okushiri (OKS). These stations and aftershocks are lined up in a direction of the strike of the aftershock distribution. This alignment has allowed us to estimate the Pn velocity for an azimuth of the strike (N190°E) without suffering from the effect of a regional variation of the Pn velocity. In order to reduce the effect of errors of hypocentral parameters, the Pn velocity was determined from a slope of differential arrival-times against the differential epicentral distances between the two stations. The Pn velocity was estimated in a range of 8.20-8.27km/s with an error of less than 0.09km/s. It is significantly greater than the Pn velocity for the corresponding azimuth of the anisotropic model proposed by OKADA et al. (1978); it agrees with the velocity for an azimuth of the maximum wavespeed (N141°E) in their model and also with the Pn velocity of 8.2km/s estimated for the Oga-Kesennuma profile which trends almost perpendicular to the present azimuth intersecting the southern part of the source area. Therefore we conclude that the uppermost mantle beneath the eastern margin of the Japan Basin does not show such an obvious anisotropy as predicted by OKADA et al. This result together with the recent result obtained in the Yamato Basin [HIRATA et al. (1987)] suggests a re-examination of the now-prevailing idea of velocity anisotropy in the Japan Sea.抄録全体を表示PDF形式でダウンロード (1264K) -
小笠原 宏, 藤森 邦夫1987 年 40 巻 3 号 p. 445-454
発行日: 1987/09/25
公開日: 2010/03/11
ジャーナル フリーSince February 1985, we have observed natural ultramicro-fracturings occurring in an area of several tens square meters at Ikuno Geophysical Observation Station in Hyogo Prefecture. From the present observation, we have attempted to obtain an adequate idea of the mechanism of the anomalous crustal deformation: it was recorded only by the extensometer No. 4 at this station before and after the Yamasaki fault earthquake (M5.6; Δ≈30km) on May 30, 1984. The Observation system was designed to detect an event occurring near the extensometer No. 4 with frequencies of 100Hz-30kHz and an amplitude larger than 30 gals. Another anomalous crustal deformation was recorded only by the same extensometer No. 4 in October-November 1985. The events that could be regarded as ultramicro-fracturings were observed in this period. The larger one had a predominant frequency of about 3kHz and a maximum amplitude greater than 50 gals. This event was observed only by the sensor near the interface between rhyolite and tuff across which the extensometer No. 4 was installed. The other was observed by two sensors also near the interface. It can, therefore, be thought that the sources of these events are near this interface and that the anomalous crustal deformation and the natural ultramicro-fracturings are probably caused by local slips on this interface. This view, however, requires more data to be investigated and confirmed.抄録全体を表示PDF形式でダウンロード (1210K) -
佐藤 裕, 許 華杞1987 年 40 巻 3 号 p. 455-457
発行日: 1987/09/25
公開日: 2010/03/11
ジャーナル フリーPDF形式でダウンロード (335K) -
青木 元, 古屋 逸夫1987 年 40 巻 3 号 p. 457-458
発行日: 1987/09/25
公開日: 2010/03/11
ジャーナル フリーPDF形式でダウンロード (256K) -
平田 隆幸1987 年 40 巻 3 号 p. 459-467
発行日: 1987/09/25
公開日: 2010/03/11
ジャーナル フリーA fracture process of rocks including earthquakes has many fractal properties in time, space, and magnitude dimensions. Gutenberg-Richter relation indicates that the fracture size distribution is a self-similar. Omori's power law means the existence of the fractal structure in time dimension. A fractal structure of the spatial distribution of earthquakes has been also reported. Furthermore, a fracture geometry of rocks is a fractal. In this paper, I review these fractal properties in rock fracture, and propose future problems concerning fractal research in earthquakes.抄録全体を表示PDF形式でダウンロード (1278K)
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