地震 第2輯
Online ISSN : 1883-9029
Print ISSN : 0037-1114
ISSN-L : 0037-1114
32 巻, 3 号
選択された号の論文の14件中1~14を表示しています
  • 大理石の破壊実験への適用
    前田 亟
    1979 年 32 巻 3 号 p. 233-241
    発行日: 1979/09/25
    公開日: 2010/03/11
    ジャーナル フリー
    A recording and reproducing system for acoustic emissions and its application to fracture experiment using marble sample are reported.
    This system consists of preamplifiers, high speed A/D converters, a digital memory unit, D/A converters, a magnetic tape (MT) unit, and a minicomputer. A. E. signals are digitized and stored in the memory. High frequency A. E. signals are converted to lower frequency ones using the memory unit. Then, the signals are transferred to a MT. The same process is repeated to send data in a MT to a computer.
    Characteristics of this system are as follows; (1) the dynamic range is 40 dB, (2) the high frequency limit of pass band is 2MHz, (3) the maximum sampling rate is 50 nsec/word, (4) the maximum emission rate in which A. E. s are correctly recorded is 200 events/sec. If the emission rate is less than 200 events/sec, A. E. activity recorded on a MT has the same statistical characteristic as that of original signals in spite of the conversion of frequency and data length.
  • 大内 徹
    1979 年 32 巻 3 号 p. 243-265
    発行日: 1979/09/25
    公開日: 2010/03/11
    ジャーナル フリー
    The frequency of earthquake occurrence in a given region can be formulated as
    dn(t)/dt=rn[1-(n/k)α]/α
    where n(t) is the number of earthquakes per unit time, r, k and α are constants. Empirically determined values of α range from 0.67 to 1.0. This is a generalization of the modified Omori formula for aftershocks, the latter being an approximation of the former for n>>k. This formula adequately describes the initial increasing and latter decreasing activities during the Matsushiro and Wakayama swarms as well as aftershocks of large earthquakes.
    When random external force is added to this system as a driving mechanism, the equation above becomes
    dv(t)/dt=-r[1-exp(αv)]/α+R(t)
    where v=ln(n/k) and R(t) is the random Gaussian noise. Repetitive seismic patterns with bursts, which are commonly observed in real earthquake sequences, are predicted from this formulation under stationary conditions. These formulations appear to be quite promising in helping to understand macroscopic features of microearthquake activities.
  • 瀬尾 和大
    1979 年 32 巻 3 号 p. 267-279
    発行日: 1979/09/25
    公開日: 2010/03/11
    ジャーナル フリー
    For the engineering purposes also, the path of the seismic waves must be investigated more clearly. Because, the seismic bedrock that is one of the most important concepts for earthquake engineering, has not been difined finally yet, and incident waves from those seismic bedrock do not always come from just below during earthquakes.
    In order to confirm this problem, the crustal structure of the Southern Kanto Region and the path of individual seismic waves during earthquakes were investigated from traveltime tables of the Japan Meteorological Agency. In this paper, earthquakes occurred in the field, that having possibility of bringing earthquake damages in Tokyo Metropolitan area, were taken into consideration.
    As results, by using stations on firm ground only, apparent velocities of P-and S-waves were obtained as 6.7km/sec and 3.9km/sec respectively from shallow and near earthquakes, and as 7.5km/sec and 4.3km/sec respectively from rather deep or distant earthquakes. On the other hand, at stations on thick sedimentary layers, systematical delay of travel-time was found. This fact was almost elucidated by existence of sedimentary layers of 2.3km thick, in case of Tokyo.
    From these studies, approximate crustal structure of the Southern Kanto Region was obtained and main paths of seismic body waves were confirmed. This result seems to be suggesting about the limitation of subsurface structure, that should be taken into consideration in the field of earthquake engineering.
  • 和田 博夫, 三雲 健, 小泉 誠
    1979 年 32 巻 3 号 p. 281-296
    発行日: 1979/09/25
    公開日: 2010/03/11
    ジャーナル フリー
    Seismicity in the northern Hida region, Japan, has been routinely observed since May, 1977 at telemeter-network stations of the Kamitakara Geophysical Observatory, and about 1500 local shocks with magnitudes greater than 0.5 have been located. (1) The observation reveals high seismicity along the Atotsugawa fault, along the northern Japan-Alps, south of Mt. Norikura and Mt. Ontake, and near Hida-Osaka, with focal depths shallower than 20km. (2) Seismic activity along the Atotsugawa fault is high at the eastern and western portions, with an intermittent zone of low activity, extending over 70km. Epicenters are deviated about 2-3km north of the fault trace, and this deviation together with focal depth distribution suggests a slightly northwestwardd dipping fault plane. All these shocks are confined above 13km, suggesting either that the fault plane extends down to this depth, or that minor brittle fractures do not take place under the depth due to some flow propertities of rock materials there. (3) Nine shocks along the fault show focal mechanisms consistent with right-lateral strike-slip evidenced by geological and geomorphological surveys (MATSUDA, 1966). (4) Heavy damage along the fault region at the time of the 1858 Hida earthquake (M=6.9) appears to indicate that this large earthquake was caused by faulting motion of the Atotsugawa fault. Most of the present seismic activity along the fault might be associated with some readjustments of residual stresses around there.
  • 広野 卓蔵
    1979 年 32 巻 3 号 p. 297-316
    発行日: 1979/09/25
    公開日: 2010/03/11
    ジャーナル フリー
    In the Kanto District, Japan, the Pacific Plate dips beneath the aseismic front at an angle of approximately 33°beneath the land, and about 40° beneath the sea where the aseismic front disappears. The boundary between these two segments underlies the Sagami Trough, suggesting that the Pacific Plate at its subduction, splits into two parts along the trough. Further, the marginal line of the upper plate passes beneath Oshima Volcano, Izu Peninsula, Shizuoka City, and then continues in a northwest direction.
    The Toyama Deep Sea Valley, about 500km long in the Sea of Japan, starts at Toyama Bay and provides the gate for another type of countercurrent to the subducting Pacific Plate. It is a slab-type one of about 280km in length. The tip of the slab, where it runs against the subducting plate surface, is converted to magma. This, in turn, exerts the pressure needed to enhance separation at the boundary between plate and crust.
    Rock breakage and/or crustal block movement result and cause earthquakes. An example is the movement of an isolated tertiary block with the dimensions of 120×75×50km3, located off south Kanto which is known to be the source of the 1923 Kanto Earthquake.
    Using the hypothesis of perfect elasticity, the fault plane of an earthquake would never be expected to strike in a direction parallel with that of the rock stream. This peculiar situation in the distribution of the direction of principal pressure for earthquake mechanism around Izu Peninsula, can thus be explained by the influence exerted by the comparatively large shearing stress of the rock stream.
  • 伊藤 潔, 黒磯 章夫
    1979 年 32 巻 3 号 p. 317-327
    発行日: 1979/09/25
    公開日: 2010/03/11
    ジャーナル フリー
    A modified master event method has been used for the pricise determination of hypocenters of small earthquake sequences that occurred within the telemetered station network of the Abuyama Seismological Observatory in the northern Kinki district, central Japan. By use of the accurate P wave arrival times of telemetered stations, this method has decreased the uncertainty of relative location of each event to its master event to be about 0.1km. And the detailed spatial distributions have been obtained for ten earthquake sequences of which magnitudes are from 2.5 to 4.0. The characteristics of the distributions are as follows; (1) The distribution of aftershocks and foreshocks of small earthquake, as well as that of large earthquake, defines a plane which seems to indicate a fault plane. (2) The trend of the aftershock area agrees with the trend of one of the nodal planes of main shock determined from the first motion of P waves. (3) Most of main shocks have been located on one end of aftershock areas and foreshocks have been located in the vicinity of the main shock. (4) The length of aftershock area is about 0.8km for M=4.0 earthquake sequence and 0.5km for M=3.0 sequence. These values roughly agree with the expolated values of UTSU's empirical equation between linear dimension of aftershock area and magnitude. The area of earthquake swarm, however, is two or three times larger than that of ususl main shock-aftershock sequence. (5) The aftershock area enlarged slightly during the activity.
  • 木村 昌三
    1979 年 32 巻 3 号 p. 329-340
    発行日: 1979/09/25
    公開日: 2010/03/11
    ジャーナル フリー
    It is pointed out that the focal distribution in central and eastern Shikoku obtained on the assumption of a structure model of four horizontal layers shows some remarkable characteristics. For example, the uppermost boundary of focal distribution of shallow earthquakes inclines downwards to the south in the Chichibu and Shimanto Belts and is very shallow in the Sanbagawa B. Therefore, in order to investigate the crustal structure in relation to such distributions of earthqakes, seismic waves generated by quarry blasts on Mt. Torigatayama, Kochi Pref. were observed at 48 temporary stations along 4 profiles of the E, NE, N and S directions. Apparent velocities are considerably different for directions of the profiles. This difference is elucidated by inclination of the crustal layers. From the travel time curves obtained, the following crustal structure model was inferred.
    P-wave velocities are estimated at 4.8, 5.5 and 6.1km/sec for three layers, respectively. Trend directions are calculated at E21-25°N for these layers. This direction coincides nearly with the tectonic axis of the Shikoku Island and the direction of the Mikabu Tectonic Line in central Shikoku. The first layer with the velocity of 4.8km/sec exists only in the southern region of the Mikabu T. L. and its thickness changes southwards from 0.6 to 3km. The lower interface of the second layer with the velocity of 5.5km/sec decends southwards with steep gradient and its thickness changes from 4 to 12km. This gradient of the upper interface of the 6.1km/sec layer is in harmony with the uppermost distribution of focal depths of shallow earthquakes. Small thickness of the 5.5km/sec layer in the Sanbagawa Metamorphic Belt compared with its surrounding regions may suggest the upheaval of the Belt by recent tectonic activities.
  • 阿部 勝征
    1979 年 32 巻 3 号 p. 341-353
    発行日: 1979/09/25
    公開日: 2010/03/11
    ジャーナル フリー
    Records of undamped Omori seismographs are found to permit fairly accurate calculation of magnitudes of earthquakes which occurred in the early years of modern seismology. Station bulletins, reports and reproduced seismograms are collected to obtain maximum amplitudes and periods. The data at Osaka Meteorological Observatory and Imperial University of Tokyo are found most useful. The Moscow-Prague formula is employed. The method is examined for 130 earthquakes fór which records of modern, damped seismographs are available. This examination is made all on the basis of Gutenberg-Richter's original worksheets to conform the present scale to the original definition of surface-wave magnitude. Station corrections are calculated. The results are successfully applied to major damaging earthquakes which occurred in Japan for 1901 to 1925, because no instrumental magnitudes were heretofore given and the epicenters are considered to be fairly accurate. The seismic activity during this period is not significantly different from the recent activity.
  • 田山実と武者金吉
    宇佐美 龍夫
    1979 年 32 巻 3 号 p. 355-359
    発行日: 1979/09/25
    公開日: 2010/03/11
    ジャーナル フリー
  • 渡辺 偉夫
    1979 年 32 巻 3 号 p. 359-360
    発行日: 1979/09/25
    公開日: 2010/03/11
    ジャーナル フリー
  • 松原 幸夫, 藤井 直之
    1979 年 32 巻 3 号 p. 360-363
    発行日: 1979/09/25
    公開日: 2010/03/11
    ジャーナル フリー
  • 吉井 敏尅, 一ノ瀬 洋一郎, 坂 守
    1979 年 32 巻 3 号 p. 363-365
    発行日: 1979/09/25
    公開日: 2010/03/11
    ジャーナル フリー
  • 谷本 俊郎, 佐藤 良輔
    1979 年 32 巻 3 号 p. 365-369
    発行日: 1979/09/25
    公開日: 2010/03/11
    ジャーナル フリー
  • 中村 一明
    1979 年 32 巻 3 号 p. 370-372
    発行日: 1979/09/25
    公開日: 2010/03/11
    ジャーナル フリー
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