巻号一覧
28 巻 (1975)
- 4 号 p. 373-
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- 2 号 p. 113-
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前身誌
28 巻, 2 号
選択された号の論文の10件中1～10を表示しています
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和田 博夫1975 年 28 巻 2 号 p. 113-124
発行日: 1975/08/10
公開日: 2010/03/11
ジャーナル フリーMicroearthquake activity near the Atotsugawa fault, one of first-class active geological faults in the northern Chubu region, has been routinely monitored since 1971.
The results obtained to data show 1) a clear lineation of microearthquakes along the Atotsugawa fault, with an intermittent zone of low seismicity, 2) less clear lineation but considerably high activity near a latent smaller fault along the Yamada river, 3) high activity with clustered epicenters just south of Mt. Norikura, and 4) extremely low seismicity over a region southeast of the Atotsugawa fault.
The above pattern of seismicity does not greatly vary with time except in the region along the Yamada river, compared with the preliminary results reported in the first paper.
Focal depths of these microearthquakes along the Atotsugawa fault are largely confined to depths shallower than 15-20km, which appears to suggest the lower boundary of the fault plane.
Composite distribution of first motion of P wave from a number of earthquakes does not seem inconsistent with right-lateral movement of the fault, indicating that maximum compressional, tectonic stresses lie in a direction slighly deviating from the E-W direction.抄録全体を表示PDF形式でダウンロード (1006K) -
海野 徳仁, 長谷川 昭1975 年 28 巻 2 号 p. 125-139
発行日: 1975/08/10
公開日: 2010/03/11
ジャーナル フリーA two-layered structure of deep seismic plane is ascertained in the central part of the Tohoku District (39°N-40°N), the northeastern part of Honshu, Japan.
This two-layered structure is found for the microearthquakes, the hypocenters of which are determined by the seismological network of Tôhoku University. A similar trend is not seen at all as for the small, moderate and large earthquakes, the hypocenters of which are determined in the same region by JMA. Our redetermination of the hypocenters of these earthquakes by using the same data of JMA, however, makes it clear that the deep seismic plane is distinctly separated into two layers.
The focal mechanism solutions for these two groups of earthquakes are derived from the superposition of the initial motions of P waves, and the opposite sense of focal mechanisms is found with each other for these two groups of earthquakes. The earthquakes that occurred in the upper layer, not only microearthquakes but also larger earthquakes, are characterized by down dip compression, that is, the pressure axis is nearly parallel to the dip of the deep seismic plane. On the other hand, microearthquakes as well as larger earthquakes, which occurred in the lower layer, are characterized by down dip extension, that is, the tension axis is nearly parallel to the dip of the deep seismic plane.
In the neighbouring regions, similar features are seen slightly, but not so distinctly compared with those in 39°N-40°N region.抄録全体を表示PDF形式でダウンロード (1234K) -
長谷川 昭, 笠原 敬司, 長谷川 武司, 堀 修一郎1975 年 28 巻 2 号 p. 141-151
発行日: 1975/08/10
公開日: 2010/03/11
ジャーナル フリーThe faulting mechanism of the Southeastern Akita Earthquake of October 16, 1970, was investigated by using both the seismic data and geodetic ones. The focal mechanism solution for the earthquake derived from the initial motions of P waves and that derived from the polarization angles of S waves indicate a reverse faulting with the pressure axis in the direction of northeast or east-northeast. The hypocentral distribution of the aftershocks which occurred just after the main shock was studied in order to discriminate the fault plane from two nodal planes. The nodal plane of S wave solution dipping to the direction of east-northeast is considered to be the fault plane from the obtained hypocentral distribution.
Rayleigh waves generated by the main shock were analysed, and the observed azimuthal distribution of amplitude spectral density is consistent with that expected from the above-stated mechanism solution. Further, the fault parameters such as fault dimensions, seismic moment, average dislocation and stress drop are estimated. The field observations of vertical tectonic movements along a near-by leveling route, strain-steps observed at the observation stations in the Tohoku District, and ground motions in the focal region are all in accordance with the faulting mechanism obtained here.抄録全体を表示PDF形式でダウンロード (1057K) -
浜口 博之, 長谷川 昭1975 年 28 巻 2 号 p. 153-169
発行日: 1975/08/10
公開日: 2010/03/11
ジャーナル フリーIn the course of examining the wide dynamic range records of the aftershocks of the Tokachi-oki Earthquake of 1968, the seventy two shocks having similar wave forms out of about 50, 000 aftershocks were found by means of a simple but systematic data sorting. High correlations in P and later phases are clear not only among the events of the same order of magnitude but also among the events with considerably different magnitudes (M=1-4.6). The recurrent occurrence of such events can be traced for the length of about 50 days, which is much longer duration compared with so-called twin or triple shocks reported so far. The activity is, as a whole, a swarm type; however, it is composed of several foreshock-main shock-aftershock sequences. The determination of hypocenters for the several large shocks shows that the events are closely distributed in space within the range of 5km, which suggests that they have common spatial and dynamical characters. Hereby, the group of earthquakes having a similar wave character can be called an Earthquake Family, which may be the most basic unit of sequence of shocks.
The nature of this family is characterized by a small b-value of 0.43 (total number=68) in the Gutenberg-Richter's formula: this result is in qualitative harmony with Mogi's explanation on b-value. The variations of P wave spectral amplitude ratio with magnitude are compared with the ω2- and ω3-theoretical source models and the ω2-model agrees well with the observed data in the frequency range between 4.6 and 16.2Hz. The average Qα in the crust is estimated to be 400 from the frequency dependence of the difference between the observed and theoretical amplitude ratio.抄録全体を表示PDF形式でダウンロード (1649K) -
山本 英二, 浜田 和郎, 笠原 敬司1975 年 28 巻 2 号 p. 171-180
発行日: 1975/08/10
公開日: 2010/03/11
ジャーナル フリーThe Iwatsuki Crustal Activity Observatory was established by the National Research Center for Disaster Prevention for the purpose of earthquake prediction research in and around Tokyo.
Because of high-level artificial noise generated by industrial activity and concentrated transportation, it is very difficult to observe microearthquakes and crustal movement with highly sensitive instruments at the surface around Tokyo.
A two-component set of tiltmeters, three-component sets of velocity seismometers and acceleration seismometers were settled at the bottom of the bored hole of 3500m depth at the Iwatsuki observatory, so that these high sensitivity observations might not be affected by the disturbance at the surface.
Contrary to our expectation, remarkable noise, however, appeared on the vertical component seismogram. It has been shown that this noise was caused by trafic cars passing by the observatory and transmitted from the surface to the bottom through the water filled in the hole.
Particularly deviced shelters were made and set in the middle of the hole to decrease the noise transmitted from the surface. Finally, satisfactory effectiveness was obtained after improvement of the shelters.
Background seismic-wave noise was simultaneously measured at the surface and at the bottom of the hole. The spectral amplitude of background noise at the bottom of the hole was about 1/301/1000 compared with that at the surface.抄録全体を表示PDF形式でダウンロード (10642K) -
1973年根室半島沖地震について鈴木 貞臣1975 年 28 巻 2 号 p. 181-199
発行日: 1975/08/10
公開日: 2010/03/11
ジャーナル フリーEpicenters of the 1973 Nemuro earthquake and its aftershocks located by USGS differ systematically from those located by the regional network of JMA. UTSU (1971) considered that JMA epicenters of earthquakes in the southern Kurile region are shifted toward the oceanic side due to large-scale inhomogeneities of the upper mantle in the island arc region.
Considering the three dimentional mantle structure, we attempted to obtain satisfactory epicenter solutions of those earthquakes using small networks in Hokkaido, Japan. Our result shows that there is a slightly systematic difference between the epicenters located by the author and those located by USGS and that the relative locations of the former are more accurate than those of the latter. The main shock parameters were assigned as follows: the latitude and the longitude, 43.09°N and 145.83°E; the focal depth, 36km; and the time of origin, June 17, 03h55m04.3s (GMT), respectively. Well-located aftershocks whose depth error is less than 10km occur only in the crust and near beneath the Moho interface.
Travel time analysis for the main shock at the JMA stations in the central and northern Japan reveals the high Pn velocity of 8.1km/sec in the uppermost mantle on the oceanic side of the Japanese arc and low Pn velocity on the continental side.抄録全体を表示PDF形式でダウンロード (1733K) -
岡野 健之助, 山崎 純一1975 年 28 巻 2 号 p. 201-206
発行日: 1975/08/10
公開日: 2010/03/11
ジャーナル フリーSimultaneous observations were carried out at Abuyama (bed rock), Nisseki (Diluvium), Aino (Alluvium) and Tonda (Alluvium), by using the vertical seismographs with same frequency response and magnification. As is generally known, the earthquake motions show strong attenuation on the bed rock, last long on the Alluvium and are intermediate on the Diluvium. But it is noted that the vibration energy concentrates at the time of S wave arrival on the Diluvium. The earthquake disaster on the hill side region may be due to this energy concentration.抄録全体を表示PDF形式でダウンロード (2260K) -
北川 豊明, 山本 清彦1975 年 28 巻 2 号 p. 207-214
発行日: 1975/08/10
公開日: 2010/03/11
ジャーナル フリーAn experiment on a tensile fracture in a glass plate with a pre-existing crack is carried out in order to elucidate the time-dependent property of anelastic deformation around a tip of extending-crack. Two types in shape of crack are prepared; one is with crack edges of circular arcs in the cross-section along the crack length by using a discgrinder and the other with non-circular edges by using a cutting machine of supersonic vibration. A crack is created by heating at a point in the direction of the major axis of the pre-existing crack, and extended toward a tip of the pre-existing crack. The time interval is measured between the time when the tip of the crack by heating is incident on a tip of the pre-existing crack and the time when a new crack is created at the other tip of the pre-existing crack. This time interval may be interpreted as the time required for the tip of the crack by heating to be propagated without loss of surface energy from a tip to the other tip of the pre-existing crack. The propagation velocity v is calculated from the time interval and the length of the pre-existing crack.
The observed time intervals are found to have a linear relation with the length of pre-existing crack in each of two types of crack shape. The values of v are estimated to be greater on an average than the terminal rupture-velocity (0.28Vp) of the tensile fracture observed in the same kind of glass plates and less than that (0.58Vp) of Rayleigh waves expected theoretically for the terminal rupture-velocity, where Vp is the P wave velocity. The values of v in the case of the pre-existing crack by disc-grinder seem to be greater than that in the case of the other.
The above time interval is alternatively interpreted as follows: If the propagation velocity of fictitious rupture-front along the pre-existing crack is considered to be equal to that of Rayleigh waves, the measured time-interval may be considered to be the sum of the time estimated from the velocity of Rayleigh waves and the time during which an anelastic deformation takes place around the tip of pre-existing crack to create a new crack. The observed time-interval suggests that the time required for the anelastic deformation increases linearly with the creek length.抄録全体を表示PDF形式でダウンロード (812K) -
MANSINHA and SMYLIE による変位場の微分式山崎 謙介1975 年 28 巻 2 号 p. 215-217
発行日: 1975/08/10
公開日: 2010/03/11
ジャーナル フリーPDF形式でダウンロード (254K) -
宇佐美 龍夫1975 年 28 巻 2 号 p. 217-219
発行日: 1975/08/10
公開日: 2010/03/11
ジャーナル フリーPDF形式でダウンロード (415K)
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