巻号一覧
33 巻 (1980)
- 4 号 p. 425-
- 3 号 p. 269-
- 2 号 p. 117-
- 1 号 p. 1-
前身誌
33 巻, 4 号
選択された号の論文の9件中1～9を表示しています
- |<
- <
- 1
- >
- >|
-
堀家 正則1980 年 33 巻 4 号 p. 425-442
発行日: 1980/12/25
公開日: 2010/03/11
ジャーナル フリーRecently, microtremors are investigated for the application to earthquake engineering, and many of these studies pay much attention to power spectrum. But, power spectrum depends not only on the underground structure of the observation site but alse on the path of propagation and the source spectrum. It is therefore important to extract the quantities of microtremors which depend only on the under ground structure. One is the phase velocity of microtremors, and another is the linear relation between radial and vertical components, if microtremors are composed only of Rayleigh wave.
In the present paper, the quantities of microtremors are derived in a statistical way. It is demonstrated that the phase velocity of vertical component of microtremors can be obtained by means of frequency-wavenumber spectrum in the case of complex wave field, and by means of phase difference between two observation points in the case of simple wave field. But, the linear relation could not be obtained, because of complex constitution of horizontal components or coexistance body waves and/or higher mode Rayleigh waves with fundamental mode Rayleigh wave.抄録全体を表示PDF形式でダウンロード (1714K) -
寺島 敦1980 年 33 巻 4 号 p. 443-463
発行日: 1980/12/25
公開日: 2010/03/11
ジャーナル フリーThe seismicity in the mining field of sulphur at Mishraq area, sited on the margin of an aseismic region adjacent to a seismic active region in Iraq, has become active since 1973 that is about one year after the start of the mining by sucking-up of sulphur melted by injected hot water.
The number of the felt earthquakes accounts to as much as 29 during 1973-1975. This shows that the seismicity increases suddenly as much as four times in comparison with the time before the start of mining.
Moreover, the area yielded the ground subsidence in the central area of the mining which caused many cracks in the surrounding area. The maximum speed of the ground subsidence was as large as -9mm/day, coinciding with the period when the seismicity was most active.
In order to decrease the ground subsidence in the field, the depth of mining has been changed shallower since August of 1975, due to which the seismicity became calm dramatically. An interesting fact was also found that the relation between the seismicity and the injected water volume per month linked so closely.
Further investigation is necessary to make clear the true causes for the change of seismicity, in and near the field, before and after the mining.
The present paper is preliminary report.抄録全体を表示PDF形式でダウンロード (1806K) -
橋本 学1980 年 33 巻 4 号 p. 465-478
発行日: 1980/12/25
公開日: 2010/03/11
ジャーナル フリーIt has been inferred [SHIONO (1977)] from the focal mechanism of earthquakes that the stress distribution in Southwestern Japan has three major characteristics;
(1) a NW-SE compression along the Nankai trough,
(2) a WNW-ESE compression in the inland region,
(3) an extension parallel to the leading edge of the Philippine Sea plate at subcrustal depths.
In order to investigate possible sources of these complex features of the stress state, a three-dimensional finite element method is applied to model the configuration and elastic properties of the Philippine Sea plate subducting under this region. In the present paper, three different types of forces and their combinations are considered;
(i) a negative buoyancy due to the density contrast between the subducting Philippine Sea plate and surrounding mantle,
(ii) a northwestward compressional force generated by the underthrusting of the plate,
(iii) a westward compressional force due to the subducting Pacific plate.
The results suggest that the parallel extension at subcrustal depths is closely associated with the configuration of the plate, and that normal faulting at these depths is mainly caused by negative buoyancy. The shear stress in the continental crust and in the subducting plate is estimated to be of the order of several hundreds bars.抄録全体を表示PDF形式でダウンロード (1281K) -
相似地震とその断層運動の平滑化水越 育郎, 森谷 武男1980 年 33 巻 4 号 p. 479-491
発行日: 1980/12/25
公開日: 2010/03/11
ジャーナル フリーBroad band and wide dynamic range observation was carried out for the earthquake swarm which was caused by the 1977 Usu Volcano eruption. The station was very near to the focal area (1-4km). The Observation system consists of three components of accelerographs (f0=3.0, h=10), and displacement seismographs of low magnification (f0=0.2, h=0.7) with multiple-frequency moduration data recorder. In addition to these, specially designed displacement seismograph of very low magnification was also used.
About 2600 earthquakes were observed during the period from December, 1977 to October, 1978. Even for the largest earthquake (M=4.3, Δ=3km) the seismogram of very low magnification was not saturated. In the displacement seismograms, very similar or almost the same seismograms are found for many earthquakes. About 1500 of the whole are distinguished to belong to twelve groups by the similarity. It is indicated that the earthquakes which belong to the same group, occurred in almost the same focal region with almost the same focal process.
For each group of the similar earthquakes, the maximum amplitude—frequency relation shows restricted amplitude range distribution but for other earthquakes which donot belong to any groups, satisfies the Ishimoto-Iida's formula.
In three groups of the similar earthquakes gradual decrease in maximum amplitudes of accelerograms (i. e, high frequency components in the spectra) with time appeared. Focal regions of the three groups were located near together in the southern part of summit crater basin in the volcano where magma eruptions occurred in the period from August to October, 1978. The decrease in high frequency component in the spectra indicates that the fault motion sequences become smooth by decrease heterogeneity in material properties in the fault. Temperature increase and argillization on the fault planes are estimated for the smoothing of the fault motions.抄録全体を表示PDF形式でダウンロード (1347K) -
―第一鹿島海山―友田 好文, 藤本 博巳, 我如古 康弘1980 年 33 巻 4 号 p. 493-499
発行日: 1980/12/25
公開日: 2010/03/11
ジャーナル フリーKashima Seamount No. 1 is placed just at the axis of the Japan Trench. Precise measurement of bottom topography which was recently carried out by the Hydrographic Department of Japan shows that the seamount is devided into landward and seaward parts by trench axis and the landward part subducts more than 1600 meters [MOGI and NISHIZAWA (1980)].
In order to investigate the origin of the seamount subduction, Bouguer gravity anomaly near and around the seamount is investigated, and it is found that there is no regionally low Bouguer anomaly which is found at any seamount in the west Pacific. The low Bouguer gravity anomaly at seamount in the west Pacific is interpreted as thinning lithosphere and the seamount is supported by the buoyancy of the asthenosphere surrounded by lithosphere. In case of Kasima Seamount No. 1, it is difficult to recognize Bouguer anomaly which shows the existence of root of the seamount supporting the mass of it. This will be the reason why part of the seamount subducts.抄録全体を表示PDF形式でダウンロード (660K) -
―黄檗断層付近における観測―安藤 雅孝, 須藤 研, 橋田 俊彦, 入倉 孝次郎, 五十嵐 千秋1980 年 33 巻 4 号 p. 501-515
発行日: 1980/12/25
公開日: 2010/03/11
ジャーナル フリーRepeated measurements of in situ P wave travel time changes was made near the Obaku fault, Kyoto, over a distance of 400m. A stack of marine air gun shots in a water-filled hole were carried out every 2 hours spanning 32 hours. By the use of a wave form correlation method, we found a half-percent variation of the travel time with an accuracy of 0.3msec. This variation of the travel time that was proved due not to errors caused by the instruments used correlates with variations in tidal stress and atmospheric pressure (10-20mb). This inferred high stress sensitivity of velocity changes (0.2bar-1) may be attributed to the presence of thin cracks. For the purpose of monitoring long term velocity changes, measurements similar to the present one are being planned over the same base line.抄録全体を表示PDF形式でダウンロード (3628K) -
宮武 隆1980 年 33 巻 4 号 p. 517-523
発行日: 1980/12/25
公開日: 2010/03/11
ジャーナル フリーNumerical simulation of aftershocks were made on a frictional faulting model with nonuniform strength combined with viscoelastic process. In this model we assumed that sliding frictional stress is proportional to strength on the each segment of the fault and that initial tectonic stress is not uniform.
It was found that decrease in aftershock numbers seems to be accorded to the modified Omori's formula and that the b-value is consistent with observations. In some cases, aftershock activity expanded from high initial stress region to a low stress region.抄録全体を表示PDF形式でダウンロード (587K) -
岡田 義光1980 年 33 巻 4 号 p. 525-539
発行日: 1980/12/25
公開日: 2010/03/11
ジャーナル フリーSpatial distributions of strain- and tilt-steps associated with two earthquakes which occurred in the region near Izu Peninsula, Japan at May 9, 1974 (M=6.9) and Jan. 14, 1978 (M=7.0) are investigated with respect to their source mechanisms.
In both cases, it is found that the observed step values do not harmonize well with the theoretically expected residual strain or tilt fields which are calculated based on an appropriate fault model. It is said that the amplitudes of steps may be considerably amplified by the effect of crustal layering and topography, whereas the polarities of them are not affected so much.
To see the circumstances of this discrepancy, critical review of similar investigations studied so far are attempted adding to the results obtained here. First, the dependence of the polarity consistency between the observed and the theoretical steps upon the epicentral distances are investigated for six earthquakes. The main results are as follows. (1) No established empirical relationships between them are found. (2) It does not always follow that the data from nearby stations are more reliable than those from distant stations. (3) In all cases, the total ratio of the polarity consistent data is about 60% for strain-steps and 50% for tilt-steps, which means a nearly random condition.
Next, the responces of the specified instruments at five stations to six earthquakes are examined only to find neither obvious peculiarities nor simple relationships between the observed and the theoretical step values.
As to strain or tilt measurement, there remains miscellaneous unknown factors which may seriously distort the signal such as local ground conditions or underground water pressures. Without the accurate knowledge about these effects, it seems to be difficult that we use strain- or tilt-step data as a material for precise argument about source processes.抄録全体を表示PDF形式でダウンロード (1481K) -
佐藤 春夫, 松村 正三1980 年 33 巻 4 号 p. 541-543
発行日: 1980/12/25
公開日: 2010/03/11
ジャーナル フリーPDF形式でダウンロード (276K)
- |<
- <
- 1
- >
- >|