All issues
Volume 32, Issue 1
Displaying 1-9 of 9 articles from this issue
- |<
- <
- 1
- >
- >|
-
Purporting to Basic Materials for Earthquake PredictionTsutomu TERASHIMA, Takashi YOKOTA1979 Volume 32 Issue 1 Pages 1-10
Published: March 25, 1979
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSIt has come to be a common knowledge that active faults are the superficial expression of shallow earthquake generation. If this is true, such an active fault along or nearby which no shallow earthquakes have still been observed is thought to be an dangerous one which has high possibility of storing such a stress enough to generate a large shallow earthquake with long recurrent period in near future.
Basing upon such idea, the writers tried to clarify such active faults as above mentioned by composing the locations of historical earthquakes with an active fault map which had been completed in Japan excepting Hokkaido area. The locations of earthquakes are shown by horizontal area representing their earthquake volumes.
Geophysical and geological study should also be made for these kind of active faults.View full abstractDownload PDF (25224K) -
Kinichiro KUSUNOSE, Kiyohiko YAMAMOTO, Tomowo HIRASAWA1979 Volume 32 Issue 1 Pages 11-23
Published: March 25, 1979
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSAn analysis is made of acoustic emissions during the deformation of granite specimen (2cm indiameter and 4cm in length) under uniaxial compression. Two kinds of granite are used in the experiment; one is coarse-grained granite whose grain sizes are between 0.5mm and 5mm, the other is fine-grained granite whose grain sizes are between 0.2mm and 1.2mm. The sizes of tensile microcracks, which radiate elastic waves, are obtained by solving observation equations from the measured quantity of inelastic volumetric strain and the estimated values of statistical parameters in the frequency-amplitude relation of acoustic emissions. According to the amplitude of event detected with a piezoelectric transducer, the estimated sizes of microcracks range from 0.4mm to 8mm for coarse-grained granite and from 0.14mm to 1.9mm for fine-grained granite. At law and moderate amplitudes of acoustic emissions, the observed frequency-amplitude relation obeys the Ishimoto-Iida's formula, but fewer large events have occurred than would have been expected theoretically. There seems to exist some critical amplitude, and at amplitudes larger than the critical one the observation deviates from the theory. The crack sizes of events having the critical amplitude are found to be about 3mm for coarse-grained granite and about 0.7mm for fine-grained granite.View full abstractDownload PDF (2949K) -
Algorithm for Optimal Disposition FindingsYutaka OHTA, Hiroshi KAGAMI1979 Volume 32 Issue 1 Pages 25-39
Published: March 25, 1979
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSAs the first step of the strategy establishment for site planning of out-door refuge places from wide-spreading earthquake fires, the formulation of an algorithm searching for optimal disposition is proposed by an application of Linear Programming Method (Transportation Problem).
In urban areas in Japan, because of consisting of overcrowded wooden houses, open spaces as for refuge from fires caused by a large earthquake are indispensably important to be considered. In many cities these refuge places have been already assigned, but in most cases, their sizes and locations are, since its assignment is too easy, unappropriate.
In this paper an examination of their appropriateness as refuge places is introduced from the standpoint of citizen's safety, under the condition that the refugee's total travelling distance should be minimized, through which a better and optimal solution was actually obtained in an exemplified city.View full abstractDownload PDF (1504K) -
Shuzo ASANO, Yoichiro ICHINOSE, Isao HASEGAWA, Susumu IIZUKA, Hiroyosh ...1979 Volume 32 Issue 1 Pages 41-55
Published: March 25, 1979
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSIn the southern Kanto district, the experiments to detect precursary change in velocity of seismic waves by means of explosion seismic method have been repeated under the earthquake prediction research project since 1968. These explosion seismic data supply good materials to obtain information on the crustal structure in the area although the distribution of observation sites is not suitable for the crustal studies. The shot points are Izu Oshima and Tateyama in the Boso Peninsula. Because of charge size and the distance of observation stations from the shot points, the information on the depth of the Mohorovicic discontinuity and Pn velocity could not be obtained.
The features of crustal structure derived from these data in addition to the existing explosion seismic data are as follows:
1) In the Boso Peninsula, thick surface layers with low velocities such as 2.5, 4.5km/s are present above the layer with a velocity of 5.6km/s.
2) Between Izu Oshima and the Boso Peninsula, there is a possibility to have a lateral change of structure. In this paper, it is assumed that this change takes place beneath the fault as indicated in the sea bottom topography, that is, the layer with a velocity of 5.6km/s on the east side contacts with the layer with a velocity of 6.0km/s beneath this place.
3) Beneath the Boso Peninsula, the layer with a velocity of 5.6km/s exists directly above the layer with a velocity of 6.9km/s, that is, the layer with a velocity of 6.0km/s is missing or very thin if exists.
4) Near Nagasa in the central part of southern Boso Peninsula, there is an offset in the upper boundaries of layers with a velocity of 5.6 and 6.9km/s.
5) In the area of Izu Oshima and the Izu Peninsula, the layer with a velocity of 6.0km/s is shallow.
6) From both shot points, Izu Oshima and Tateyama, the layer with a velocity of 6.9km/s becomes shallower toward the Boso Peninsula and Dodaira, while it becomes deeper toward the Izu Peninsula.
7) Near Izu Oshima, the layer with a velocity of 6.9km/s becomes fairly shallower almost independent of the direction of profiles.View full abstractDownload PDF (1453K) -
Yoshimasa KOBAYASHI1979 Volume 32 Issue 1 Pages 57-73
Published: March 25, 1979
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe Great Kanto earthquake, 1923, triggered a catastrophic debris flow which devastated the village of Nebukawa with a loss of 300 to 400 lives. The buried area at Nebukawa is determined by synthesizing eyewitness accounts, photographs, the character of surface soils, etc. The moment of rushing at Nebukawa is estimated at about 5 minutes after the mainshock onset from the eyewitness accounts and aftershock records. The temporal change in topography in the mountain region is investigated by comparing topography maps prior and after the earthquake, and a probable source of the debris flow is assumed at a large depressed area, Obora about 4km upstream Nebukawa. The grain-size distributions of the debris-flow deposits and those of mountain soils are also consistent with this assumption.View full abstractDownload PDF (8371K) -
Latest Crustal Dynamics along the Northern Boundary of the Philippine Sea PlateYoichiro FUJII1979 Volume 32 Issue 1 Pages 75-88
Published: March 25, 1979
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSSome remarkable geophysical events have been prevailing since 1974 along the northern boundary of the Philippine Sea Plate. A series of crustal activities such as occurrence of the 1974 Izu-Hanto-Oki earthquake, 1976 crustal upheaval and related swarm earthquake, and occurrence of the 1978 Izu-Ooshima-Kinkai earthquake was observed during the period 1974-1978 in and around the Izu Peninsula, Japan. A small crustal upheaval and related swarm earthquake activities in and near the Boso peninsula, the south Kanto district, were also observed during approximately the same period of crustal activities in the Izu peninsula. Recently acceleration of crustal subsidence near Omaezaki promontory and crustal upheaval near Mikkabi were detected in the Tokai district.
The author regards these geophysical phenomena to be related each other and tries to interpret them in terms of plate tectonics. The upper part of the convergent boundary of the Philippine Sea Plate had been completely locked throughout the concerned period, while the deeper part slipped aseismicaly some times along some parts of the plate boundary. At first the deepest part of the convergent plate would go down aseismicaly under the Tokai district, and this down-going might cause Mikkabi uplift and Omaezaki subsidence acceleration. When subduction of plate was accelerated at a place of convergent plate boundary, this acceleration propagated to another place causing an eventful aseismic slip. Thus, a series of crustal upheaval and related earthquake activity was observed.
As for the future activities of the observed geophysical events, we have two possibilities. The one is occurrence of the Tokai (Suruga-Bay) earthquake as the consequence of forwarded propagation of deep dislocation to the upper part of the plate boundary. The another is stagnation of the deep creep dislocation. A question which way is possible may be one of keys in the prediction of the future Tokai earthquake.View full abstractDownload PDF (1327K) -
in Relation to Tectonics in and around the Izu PeninsulaNorio YAMAKAWA, Akio YOSHIDA, Masahiro KISHIO1979 Volume 32 Issue 1 Pages 89-101
Published: March 25, 1979
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe characteristics of the space-time distribution of foreshocks and aftershocks of the Izu-Oshima-Kinkai Earthquake of 1978 are investigated, and tectonics in and around the Izu Peninsula is discussed.
The overall distribution during the period investigated in this research is composed of three parts, the group I which spreaded in the sea near the Izu Oshima, the group II which extended to WNW direction in the Izu Peninsula and the group III which linked with the group II at the western end and stretched to the conjugate SSW direction. Among these three groups comparatively large aftershocks occurred in the last group. In the groups I and II aftershocks occurred just after the occurrence of main shock but there seems to have been some time till earthquake occurrence in the group III, though it is not certain when the activity of the group III accurately commenced.
The aftershocks of the Izu-Hanto-Oki Earthquake of 1974 which extended to the Amagi mountain and those of the Oshima-Kinkai Earthquake of 1978 in the Izu Peninsula are not overlapped each other.
In the Izu Peninsula, active faults of WNW-ESE direction are conspicuous and conjugate faults are also observed. And the earthquakes of magnitude larger than 5.0 which occurred in the Izu Peninsula in the last 50 years are all considered to be attributed to activities of these conjugate faults systems.View full abstractDownload PDF (1391K) -
The Tokachi-oki Earthquake of May 16, 1968Mamoru KATSUMATA1979 Volume 32 Issue 1 Pages 103-104
Published: March 25, 1979
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (231K) -
Katsuhiko ISHIBASHI, Yoko OTA, Tokihiko MATSUDA1979 Volume 32 Issue 1 Pages 105-107
Published: March 25, 1979
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (470K)
- |<
- <
- 1
- >
- >|