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Volume 25, Issue 4
Displaying 1-13 of 13 articles from this issue
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Part 4. Progression of Fracture on the Fault PlaneMichio OTSUKA1972 Volume 25 Issue 4 Pages 275-282
Published: March 30, 1973
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSA chain reaction type source model which was introduced in the Part 2 of this paper to calculate the magnitude-frequency relation of earthquakes has been used to simulate the spatial progression of fracture in the source domain. An example is demonstrated, which provides many suggestions toward understanding the processes that might be occurring in the source domain.
The multiplicity in the seismic records, shape of the damaged regions and of aftershock area, rupture velocity etc. are some which are expected to be comprehended by introduction of this model.View full abstractDownload PDF (740K) -
Tsutomu TERASHIMA1972 Volume 25 Issue 4 Pages 283-294
Published: March 30, 1973
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThis is a report on disaster of Hachijo-jima island (about 300km southwards from Tokyo) caused by the shock (M=7.2) that occurred in offshore Hachijo-jima island on February 29, 1972.
Intensity by this shock are V at Hochijo-jima island and IV in Kwanto area (JMA Intensity scale). The acceleration at the lobby of I. I. S. E. E. was 78 gals p-p (3Hz).
Luminous phenomenon was observed by many inhavitants.
Disasters distributed mainly the center and the southeastern part of the island. Damage concentrated on ledged roads and reservoirs.
Houses suffered lightly from the earthquake for its magnitude. It may come to this that the island is composed of igneous rocks and the houses are made strongly against horizontal stress as this island is in the zone of strong wind through the year.View full abstractDownload PDF (7407K) -
Takashi TADA, Kumizi IIDA1972 Volume 25 Issue 4 Pages 295-301
Published: March 30, 1973
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe relationships between the predominant period and the magnitude of the microearthquakes were studied. We assume the relationship in the following form. LogT=a+bM where, T is the predominant period in second and M is the earthquake magnitude. The following results were obtained, LogT=-1.50+0.50M (P wave, microearthquakes occurred in the vicinity of the Neo-Valley) LogT=-1.12+0.45M (S wave, microearthquakes occurred in the vicinity of the Neo-Valley) LogT=-1.38+0.44M (P wave, microearthquakes occurred in the vicinity of the Inuyama City) LogT=-2.03+0.65M (P wave, Matsushiro earthquake swarm) LogT=-1.45+0.40M (whole P wave). From the dislocation theory, the relation of T and M is derived as follows, LogT=-0.3-0.7 Logσ+0.5M. (1) where, σ is the stress drop in bar. Substituting σ=40 bars into (1), we get LogT=-1.4+0.5M. (2) This equation agrees well with the above mentioned results. But, when σ is not constant, the equation (1) suggests that the difference of the predominant period in the same earthquake magnitude is the differences of the stress drop. Indeed, the deviations of the data are so large that the stress drops seem to be not constant.
The predominant periods of the Matsushiro earthquake swarm are shoter than those of the other microearthquakes. This evidence may relate to the characteristics of the Matsushiro earthquake swarm.View full abstractDownload PDF (535K) -
Noboru YAMAGISHI, Toshikatsu YOSHII1972 Volume 25 Issue 4 Pages 302-309
Published: March 30, 1973
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSAttenuation coefficients of the PL waves are determined from the records at three stations in Japan. The coefficients are from 0.7 to 2.6per 1000km. They show a clear tendency with period, and are well explained by the imaginary part of the complex root of the period equation for a crustal model JW-1 by YOSHII (1970).View full abstractDownload PDF (679K) -
Takashi TADA1972 Volume 25 Issue 4 Pages 310-317
Published: March 30, 1973
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSP wave velocity distribution in the down going slab near the Japanese islands arc was studied by the travel time curves derived from the deep focus earthquakes.
The P wave velocity in the down going slab is higher than the surrounding normal mantle: about 5, 3.5, and 2.5% at the depth of 200, 400, and 600km respectively. The velocity anomaly of 5% corresponds to the temperature anomaly of about 1000° at the depth of 200km. This value agrees well with the theoretical temperature anomaly in the down going slab by many other authors.
The low velocity layer in the down going slab may not be existent, but the low velocity layer in the surrounding normal mantle near the Japanese islands arc may begin beneath the Moho discontinuity and the depth of the minimum velocity is about 100km.
The existence of the olivine-spinel phase transitional layer in the down going slab is not still clear.View full abstractDownload PDF (711K) -
Jiro SEGAWA1972 Volume 25 Issue 4 Pages 318-332
Published: March 30, 1973
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSA new type processor of the Tokyo Surface Ship Gravity Meter (T. S. S. G.) has been designed. It makes use of a pulse train logics with which we can perform addition, subtraction, product and division of frequency of an electronic signal without transforming it into a digital form, so that this device eliminates use of a common digital computer. By the use of this device we can remove completely and at very low cost the non-linear rectification error which has been thought inherent with the T. S. S. G.View full abstractDownload PDF (1318K) -
Ichiro KAWASAKI, Yasunori SUZUKI, Ryosuke SATO1972 Volume 25 Issue 4 Pages 333-342
Published: March 30, 1973
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSTheoretical expressions for surface displacements due to a double couple source in a semiinfinite medium are derived in Part 1 of this paper when seismic moment is a ramp function of time.
In the present paper, results of numerical computations for a case of a point source are presented. Basic characteristics of each phase are summarized as follows;
P pulse has basically rectangular form. Confining to the onset of P pulse, initial amplitudes in a semi-infinite medium are, even in rather near field, close to those in an infinite medium with correction of surface effect due to plane wave incidence.
SP pulse, which is generated from the source as S phase, incident onto the free surface with critical angle and then propagated along the surface as P phase, has relatively large amplitude in near field and cannot be neglected when discussing wave form on the free surface.
Forms of S pulse are quite different at epicentral distances less than and greater than the critical distance. S pulse beyond the critical distance has logarithmic infinities at arrival time of S phase, ts, and ts+t0, t0 being rise time of the source function. Therefore plane wave correction cannot be applied successfully as it can be done for the onset of P pulse.
Rayleigh pulse is well developed when epicentral distance is about five to ten times as large as focal depth and its form is not affected very much by the rise time of source function.
For the surface focus, S pulse has no logarithmic infinity but Rayleigh pulse has infinities at arrival times tR and tR+t0.View full abstractDownload PDF (743K) -
Isamu AIDA1972 Volume 25 Issue 4 Pages 343-352
Published: March 30, 1973
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe numerical estimation of the geometry of a tsunami source is carried out in two steps; 1) The wave patterns offshore of a bay are computed by the characteristics method from the tide-gage record obtained within a bay, which are used as the fictitious boundary data in the comparison with the numerical results, 2) The best fitting for the reference waves of the numerical results derived from the assumed source deformation consisting of 9 unit sources is determined by the least square method making use of the theorem of superposition. The simplest source model estimated in the case of the 1968 Hyuganada Tsunami is the nearly uniform upheaval of 30-35cm whose area is 80×32km2. The correlation coefficients between the estimated and the observed waves at the stations along the coast of Kyushu and Shikoku are 0.7 to 0.9. This source model is appreciably different from the pattern of the crustal deformation expected from the earthquake mechanism, though the reason is not clear at present.View full abstractDownload PDF (1033K) -
Tetsuo TAKANAMI, Souichi HISAMOTO1972 Volume 25 Issue 4 Pages 353-361
Published: March 30, 1973
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSA considerable large earthquake with the focal depth=0km and the magnitude=6.9 occurred off southwestern Sakhalin at 03h 36m (JST) on September 6, 1971.
At Wakkanai, the number of one hundred and forty two felt and unfelt shocks were counted up during the period from September 6, 1971 to the end of October.
For the purpose of studying the crustal structure with travel time analysis, we selected six shocks out of them under the condition that the source depths were zero and the magnitudes were beyond 5.0.
Then the individual arrival time was read with the accuracy in 0.1 seconds and a few apparent velocities had been determined with the least squares method.
We are sure that the following some conclusions have been inferred from the present work.
At first, seismicity in southwestern Sakhalin may be not always low.
Next, according to the apparent velocity feature, Hokkaido, as a whole, may be roughly intothree parts; One of them is the inner part including the stations of Obihiro, Urakawa, Muroran and elsewhere which have characteristic feature of crustal structure with lower velocity. On the contrary, the other two groups consist of the stations in the most western side and the Pacific Ocean side having characteristic feature of structures with higher velocity.
These three regions show about 7.7-7.8km/sec and about 8.1-8.3km/sec for inner part and for the most western and the Pacific sides as their apparent velocities respectively.
Above all, anomalous short travel times have been always obtained at station Suttsu in the most western part.
And some large earthquakes had occurred occasionaly off and near Rumoi located in the western Hokkaido.View full abstractDownload PDF (838K) -
Tokutaro HATORI1972 Volume 25 Issue 4 Pages 362-370
Published: March 30, 1973
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe Erimo-oki and Hachijo-oki tsunamis were generated at a junction of two trenches, accompanying the earthquakes of magnitude M=7.0. According to the author's method, based on the attenuation of tsunami height with distance, the magnitudes of the Erimo-oki and Hachijo-oki tsunamis are m=-0.5 and 0.5, respectively. The estimated tsunami source of the Erimo-oki tsunami is located on the deep-sea terrace and its west side is in contact with the source of the 1968 Tokachi-oki tsunami. The source area of the Hachijo-oki tsunami elongated along the Izu-Bonin trench meets with that of the 1953 Boso-oki tsunami on the Japan trench. The source dimensions of two tsunamis seem to be 40-60km.
The recorded initial motions of both tsunamis were either “up” and “down” directions. Judging from these features of the Erimo-oki tsunami, the south side of tsunami source may have subsided and the north side uplifted. The sense of the source deformation inferred from the tsunami records agrees with that of the seismic data in Hokkaido, but the data in Honshu do not. In case of the Hachijo-oki tsunami, the subsidence of the sea-bottom may have occurred in the west side of the source. By applying the corrections for the refraction and shoaling, the sea-level disturbances at the tsunami source are inferred approximately from the initial waves observed at the coast as follows: The calculated value of the Erimo-oki tsunami is in the range of -5-+10cm and that of the Hachijo-oki tsunami -20-+5cm. The pattern of sea-level disturbance may suggest the fault type for earthquake.View full abstractDownload PDF (885K) -
Hitoshi TAKEUCHI1972 Volume 25 Issue 4 Pages 371-372
Published: March 30, 1973
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (249K) -
Hisashi MIYOSHI1972 Volume 25 Issue 4 Pages 372-374
Published: March 30, 1973
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (339K) -
Hisashi MIYOSHI1972 Volume 25 Issue 4 Pages 374-376
Published: March 30, 1973
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (308K)
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