巻号一覧
49 巻 (1996 - 1997)
- 4 号 p. 423-
- 3 号 p. 285-
- 2 号 p. 141-
- 1 号 p. 1-
前身誌
49 巻, 2 号
選択された号の論文の12件中1～12を表示しています
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気象庁に保存されている地震記録の写真について武村 雅之, 浜田 信生1996 年 49 巻 2 号 p. 141-168
発行日: 1996/08/23
公開日: 2010/03/11
ジャーナル フリー96 photographs of seismograms from the 1923 Kanto earthquake (M=7.9) have been preserved at JMA (the Japan Meteorological Agency). These seismograms were obtained at meteorological observatories in and around Japan and Tohoku Imperial University in Sendai, whose epicentral distances are within about 2000km. P-wave forms of the main shock are recorded at 37 observation stations, though larger shaking parts of the ground motions are saturated on the records at almost all the stations. First, a type of seismograph and its instrumental characteristics are examined for each record from old materials and old records preserved at JMA. It is found that the seismograms at 29 stations were recorded by Portable Seismographs with natural period T of about 5sec and magnification V of 10 to 100, and most of the others by Omori's Seismographs with T of 10 to 30sec and V of 10 to 20 and by Wiechert Seismographs with T of about 5sec and V of about 100. Secondly, P-wave characteristics of each record are examined. We reexamined polarities of initial P-wave motions and reviewed focal mechanisms obtained for the Kanto earthquake. We also found that P-wave forms at many stations have some characteristics in common. The P-waves begin with small amplitude and the first remarkable phase with a large amplitude appears after the duration of the initial small phases. The second remarkable phase is also identified several seconds after the first remarkable phase, irrespective of the epicentral distances of the stations. The duration time τ01 of the initial small amplitudes correlates with the epicentral distance at each station. It can be explained by the difference of calculated arrival times between Pn and Pg phases or between Pn and P* phases in addition to a duration of the initial small rupture near the hypocenter. The duration of the initial small rupture is evaluated about 4.5sec from τ01's at observation stations within the epicentral distance of 170km. In the meantime, the difference τ12 of arrival times between the first and the second remarkable phases correlates with the azimuth angle of each station from the epicenter. Geometry and difference of occurrence times of big subevents are evaluated on the fault plane of the main shock from the data of τ12's, if we assume the two remarkable phases are due to two big subevents, respectively. The second subevent is located about 40km distant from the first subevent in the direction of about N 100°E, and the time interval of the occurrences of the two subevents is about 14sec.抄録全体を表示PDF形式でダウンロード (4741K) -
開原 貴美, 堀内 茂木, 長谷川 昭, 仁田 交市, 河野 俊夫, 堀 修一郎, 笠原 敬司1996 年 49 巻 2 号 p. 169-177
発行日: 1996/08/23
公開日: 2010/03/11
ジャーナル フリーA seismic array network composed of 90 stations with intervals of 10m was set up along a road in the western part of the Nikko-Ashio area, northern Kanto, Japan. Observed seismograms of local events show that the amplitude of seismic waves changes by several times for a difference of locations of several tens meters. This change is considered to be caused by a heterogeneous sedimentary layer just beneath the array stations. Since a large spatial variation of waveforms caused by the heterogeneity at shallow depths prevents us from making detailed studies on a deep structure, we determined a precise shallow structure beneath the array by firing land airgun shots and making mallet shots with intervals of 50m and 10m, respectively. The obtained shallow structure along a 380m long observation line shows that the value of P-wave velocity for the basement rock is 3.5km/s and that the thickness of the sedimentary layer, whose P-wave velocity changes from 0.5km/s to 2.0km/s, is around 30m. Synthetic seismograms calculated by the finite difference method for the obtained velocity model show that the observed amplitude distribution of P-waves can be explained by the obtained velocity model. However, observed coda waves are not well reconstructed. The synthetic seismograms for coda waves suggest that a low velocity sedimentary layer having a large lateral velocity change produces surface waves of a large amplitude even in a case of vertical incidence of P waves. Since the amplitude of the excitation and the propagation direction of the surface wave are strongly affected by a three dimensional structure of the sedimentary layer, it seems very difficult to fully estimate site effects from the obtained two dimensional surface structure. These results suggest the importance of putting seismometers on a layer with a high seismic velocity and developing a new filtering technique to remove surface waves of very low apparent velocity in an analysis of the deep structure.抄録全体を表示PDF形式でダウンロード (1329K) -
1984年長野県西部地震島田 篤, 宮武 隆, 谷山 尚1996 年 49 巻 2 号 p. 179-191
発行日: 1996/08/23
公開日: 2010/03/11
ジャーナル フリーHigh acceleration ground motions close to the fault of the 1984 Nagano-ken-Seibu earthquake are simulated using a finite difference calculation. The source is modeled by dynamic crack propagation. The distribution of the dynamic parameters, (e.g., stress drop and rupture time) on the fault are recovered with constraint of waveform inversion results inferred by YOSHIDA and KOKETSU (1992). Considering the limitation of numerical computation, we discuss 2Hz low-pass-filtered ground velocity and ground acceleration. Calculated maximum ground velocity and acceleration are 80cm/s and 600cm/s/s, respectively. The distribution of low-pass-filtered peak ground velocity and acceleration shows that high acceleration is generated near the high stress drop asperity at the depth of about 2km. This region corresponds to the area of high acceleration greater than 1g suggested by thrown-out stones [UMEDA et al. (1987), IIO et al. (1992)].抄録全体を表示PDF形式でダウンロード (6227K) -
堀家 正則, 竹内 吉弘, 今井 智士, 藤田 崇, 横田 裕, 野田 利一, 井川 猛1996 年 49 巻 2 号 p. 193-203
発行日: 1996/08/23
公開日: 2010/03/11
ジャーナル フリーA survey of the geological subsurface structure was conducted in the east of the Osaka basin in order to predict seismic motions. The reflection survey revealed a detailed P-velocity structure down to the basement rock embedded at a depth of 1.5km to 1.7km. The features appearing commonly in reflection profiles of the Osaka basin are comfirmed in the reflection profiles as well: the sediments are divided into a shallow layer composed of alternate stacks of marine and non-marine deposits and a deep layer composed of only non-marine deposits. The array analyses of microtremors also revealed S-velocity structures down to the basement rock, using the inversion of microtremor phase velocities. Furthermore, a two-dimensional east-west subsurface structure model of the Osaka basin is proposed, combining geological information obtained by present and past surveys.抄録全体を表示PDF形式でダウンロード (1824K) -
岩佐 幸治, 吉岡 直人1996 年 49 巻 2 号 p. 205-215
発行日: 1996/08/23
公開日: 2010/03/11
ジャーナル フリーIt is known that the real area of contact is much less than nominal contact area when rough surfaces come into contact. The fact that in general we can not directly observe real contacts makes the contact problem difficult in intuitive recognition. Computer simulation is one of the ways that enable us to observe the contact spots directly on a computer display. Using three-dimensional topographies, a computer simulation was performed to see how the real area of contact changes when a contacting surface moves over the other. We can see each contact spot being created, growing and being eliminated with increasing horizontal relative displacement. The animation provides a basic recognition of changing contact spots with increasing displacement. We applied the animation to the interpretation of Dc in the so-called rate and state variable friction law. The result shows that Dc is the displacement required for a complete replacement of real contact area that existed at the moment of step change in slip rate. The computer simulation is a powerful means in investigating the physical process of friction.抄録全体を表示PDF形式でダウンロード (1398K) -
相田 勇1996 年 49 巻 2 号 p. 217-226
発行日: 1996/08/23
公開日: 2010/03/11
ジャーナル フリーFor the purpose of investigating tsunami characteristics in Tokyo bay, a number of seismic fault models with the magnitude M=7.0 that could possibly occur underneath the Tokyo bay area are assumed and tsunami generations due to them are studied numerically. It becomes clear that the maximum tsunami height along the bay coast is nearly equal to the total vertical displacement of sea floor, i. e. the sum of maximum uplift and subsidence of sea bottom caused by faulting. A mode analysis of water oscillation in Tokyo bay is carried out. The second mode (N=2, T=71min) of bay water oscillation often predominates as tsunami waves. In Tokyo Harbour, current velocity of tsunami reaches about 2m/s at the harbour entrance for a model, for which the maximum tsunami height is equal to about 1m.抄録全体を表示PDF形式でダウンロード (1245K) -
八木原 寛, 角田 寿喜, 宮町 宏樹, 後藤 和彦, 平野 舟一郎, 日野 亮太, 金澤 敏彦, 海宝 由佳, 塩原 肇, 渡邊 智毅, ...1996 年 49 巻 2 号 p. 227-239
発行日: 1996/08/23
公開日: 2010/03/11
ジャーナル フリーWe investigated seismic activity around Tokara Channel north off Amami Oshima, Nansei Syoto (Ryukyu) Islands of western Japan, using 12 ocean-bottom seismographs (OBS), as well as two temporal stations at Yaku Shima and Amami Oshima islands, operated from April 16 to May 10, 1992. One-dimensional velocity structure and station corrections were inverted from P and S times of 51 events provisionally well-located in the OBS network. We then relocated precisely 239 events in the studied region, using the inverted velocity structure and station corrections.
Seismicity was highest in an area of about 10km×10km near the trench axis northeast off the OBS network: the largest event of MJMA 5.6 and other 40 events (probably aftershocks) were located at shallow depths. A mechanism solution of normal fault type with a T-axis of NW direction for the largest event was concordant with bending process of the Philippine sea plate. On the other hand, 18 events at depths of about 30km in a small area north of the OBS network were presumably due to interplate thrusting, because a composite mechanism solution for three events was of reverse fault type with a P-axis of ESE direction. A cluster of 17 events at depths from 10km to 25km was found in a southwest area of the network. These shallow events were probably crustal earthquakes within the Eurasian plate.
We found an area of very low seismicity in the southeast of the network during the period studied. It is also identified at the nearly same location in the epicenter distribution from 1984 through 1991 obtained by Japanese Meteorological Agency (JMA) and possibly corresponds to the aftershock area of the 1911 Kikaijima Earthquake (M 8.0).
Although we could not confirm any discernible alignments of shallow earthquakes along the Tokara Channel which is a notable tectonic line, the dipping angle of the intermediate-deep seismic zone changes discontinuously from about 65° on the north of the channel to about 40° on the south.抄録全体を表示PDF形式でダウンロード (1675K) -
羽鳥 徳太郎1996 年 49 巻 2 号 p. 241-247
発行日: 1996/08/23
公開日: 2010/03/11
ジャーナル フリーA relation of tsunami and earthquake magnitudes is investigated based on the tsunami catalogs for tsunamis generated in South America during the period from 1562 to 1995. It was compared with a statistical relation formerly derived from Japanes data and some great tsunamis in the world. As the result it is shown that the relation is normal for earthquakes with magnitudes, M>8.0, but the tsunami magnitudes (Imamura-Iida scale, m) exceed by 1-2 grade (tsunami heights: 2-5 times) for the earthquake magnitudes with M<7.6 in the North Chile to South Peru region. Using a formerly derived empirical relation between tsunami potential energy at the source and the tsunami magnitude, we estimated the tsunami energy distribution at intervals of 1, 000km. The result shows that the cumulative energy is in the order of 1021-1022 ergs and largest, 3.2×1022 ergs, in South Chile. Chile, Peru and Ecuador-Colombia occupy 70, 24 and 6% of the total energy as the source region, respectively. Since 1586, eight large tsunamis with the earthquake magnitude, M, over 8.0 and the tusnami magnitude, m, over 3 have hit Japan because of the directivity effect. There is a seismic gap growing in North Chile, which is noticed from the cumulative curve of the tsunami energy in the 1, 000km range.抄録全体を表示PDF形式でダウンロード (677K) -
宮島 力雄, 山内 常生1996 年 49 巻 2 号 p. 249-252
発行日: 1996/08/23
公開日: 2010/03/11
ジャーナル フリーPDF形式でダウンロード (371K) -
山内 常生, 宮島 力雄1996 年 49 巻 2 号 p. 253-256
発行日: 1996/08/23
公開日: 2010/03/11
ジャーナル フリーPDF形式でダウンロード (2329K) -
加藤 尚之1996 年 49 巻 2 号 p. 257-275
発行日: 1996/08/23
公開日: 2010/03/11
ジャーナル フリーAseismic sliding in the earth plays an important part in time-dependent stress concentration and relaxation, which significantly affect the occurrence of earthquakes. I review 1) observations of fault creep, slow and silent earthquakes, and pre- and post-seismic sliding in the earth, 2) experimental studies on stable sliding, episodic sliding, and preseismic sliding on artificial faults in rocks, and 3) constitutive laws of rock friction derived from laboratory studies and its application to the modeling of aseismic sliding in the earth. It is concluded that the dependence of rock friction on slip and/or slip-rate is essentially important for the mechanism of aseismic sliding. Detection of the occurrence of aseismic sliding is effective in understanding the earthquake generation process.抄録全体を表示PDF形式でダウンロード (3055K) -
高田 淑子1996 年 49 巻 2 号 p. 277-283
発行日: 1996/08/23
公開日: 2010/03/11
ジャーナル フリーSmoothed Particle Hydrodynamics (SPH) method and its application to planetary sciences, particularly to impact problems, are reviewed. The SPH method is a Lagrangian particle method. It is suitable for three dimensional fluid dynamic problems with large distortion or fragmentation, since it does not require any grids. Fundamental idea and equations are introduced. Then, the application to impact problems of planetary sized bodies and asteroidal sized bodies is discussed. The method is extended to the elastic-plastic bodies to model the fracture and the fragmentation of materials. Further application to various fields of fluid dynamic studies, such as, earth sciences, is breifly addressed.抄録全体を表示PDF形式でダウンロード (2652K)
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