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Volume 28, Issue 3
Displaying 1-12 of 12 articles from this issue
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Tsutomu TERASHIMA, Masakazu OHTAKE, Kunio OZAWA1975 Volume 28 Issue 3 Pages 239-267
Published: October 10, 1975
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSRecently, it is suggested that underground water plays an important part in generating the earthquakes. Studies are made in the present paper on changes in flow rate, temperature and heat capacity of hot springs distributed in southern Izu peninsula. These changes are considered to be related closely with the change of underground water caused by the Izu-Hanto-Oki (off the Izu peninsula, Japan) Earthquake (138°48′E, 34°34′N, h: 10km, M=6.9, May 9, 1974).
Both of the flow rate and temperature of these hot springs were found to be increased just after the earthquake.
Increases of flow rate and heat capacity discharged in the Shimogamo spa contiguous to the epicentral area began about 5.7 years before the earthquake. This abnormality reverted just before the earthquake. This period of about 5.7 years fit the period of precursory phenomena prior to the occurrence of the earthquake M=6.9 expected by “Dilatancy Model”. Moreover, the behavior of the variation bears a close resemblance to what is expected for the behavior of underground water as precursory phenomena prior to earthquakes by “Dilatancy Model”.View full abstractDownload PDF (2237K) -
Tokihiko MATSUDA1975 Volume 28 Issue 3 Pages 269-283
Published: October 10, 1975
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe recurrence interval (R) of earthquakes from a given fault-segment is related to the long-term slip-rate (S) and the displacement accompanying an earthquake (D). The relation is expressed as R=D/S [WALLACE (1970)], when aseismic fault creep is disregarded. D has a relation with the earthquake magnitude M as logD(meter)=0.6M-4.0 for Japanese inland earthquakes. Then, the relation R to M is expressed as logR=0.6M-4.0-logS.
It is proposed here that a given fault-segment has a constant value in D through time during late Quaternary period. Values D and M may be different between different faults or segments, but there is a proper value D0 or M0 for a given fault or its segment. Historic records on Japanese earthquakes seem consistent with this assumption. D0 or M0 is obtained from data of historic earthquakes or from a unit offset of geologic references.
Fault length L is proportional to a dimension of strain domain, and it represents the maximum magnitude from the fault. The relation of L to earthquake magnitude M is logL(kilometer)=0.6M-2.9 for Japanese inland earthquakes. Then, maximum magnitude ML from a fault is expressed as ML=(1/0.6)logL+4.85.
When a given fault or its segment has no earthquake during at least t years up to the present, the accumulated earthquake energy during t years is expressed as Mt=(1/0.6)log(t·S)+6.67.
Thus, a probable maximum magnitude Mmax from a given fault or its segment is expressed as Mt<Mmax<ML. Examples of the above procedure and its result are described.View full abstractDownload PDF (1338K) -
Fumiaki KIMATA, Rikio MIYAJIMA1975 Volume 28 Issue 3 Pages 285-292
Published: October 10, 1975
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSTwo temporary stations were set up at Kosugihara and Iriya in order to examine the grouth of the aftershock area of the Earthquake off Izu Penisula (May 9, 1974). In addition to the observations at these two temporary stations, available data recorded at Kunosan, Kumomi, Kawazu, Okuno and Inuyama were used in this study. The results obtained are as follows.
(1) Definite grouth of the aftershock area was not found. The area, however, seemed to be elongated from the epicenter of the main shock (determined by Aoki) to north-east along the faults, which turned out to be an earthquake swarm at Amagi.
(2) The earthquake swarm at Amagi are considered to be caused due to the pressure axis trending N-S, the same stress field as the main shock.
(3) The magnitude-frequency relation of aftershock and Amagi earthquake swarm was well represented by Gutenberg-Richter's formula logn(M)=a-bM with b=1.1. The frequency-time relation was well represented by the modified Omori's formula with the parameter indicating rapid decrease of aftershocks.View full abstractDownload PDF (656K) -
Kazunari FUJII, Ichizo YAMAOKA, Masayoshi NAKANO1975 Volume 28 Issue 3 Pages 293-301
Published: October 10, 1975
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSA calculation is performed about multiple scattering of cylindrical P waves, by parallel N+1 cylinders encircling the wave-source. It is assumed that the cylinders are all rigid, fixed immovably on a circle arround the source. The potentials, sφ1 and ∑′tφ1, denoting the first order-scatting by the s-th and other N cylinders, respectively, are firstly obtained and those of the l-th order-scattering then derived, through mathematical induction. Addition theorem of Bessel function is frequently used in order to expreess these potentials only in terms of the polar coordinate at the s-th cylinder. Finally the expressions of ∑′tφl in distant region are derived, by repeated applications of the above addition theorem.
Relative decrease or increase of pressure for scattering is numerically computed on two cases of N=1 (i. e. 2 cylinders are located) and 100. Theoretical results obtained here may be applied to practical problems, such as the protection of aquatic animals against under-water explosions.View full abstractDownload PDF (715K) -
Tokuji UTSU1975 Volume 28 Issue 3 Pages 303-311
Published: October 10, 1975
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSA correlation has been found between intermediate earthquakes in Hida (the region around the city of Takayama) and shallower earthquakes in central Kwanto (the region around the city of Tokyo). Among 61 earthquakes of M≥5.5 in central Kwanto during the 51 years from 1924 through 1974, 37 earthquakes occurred in the one-year periods centered by the times of 16 earthquakes of M≥5.0 in Hida. The probability that 37 or more earthquakes in central Kwanto occur during those periods (total length=14.46 years) is 1.5×10-7, if the Kwanto earthquakes are distributed randomly in time. It seems impossible that the smallness of this probability is wholly attributed to some effects other than the true correlation, such as the selection of data, the clustering of earthquakes, etc. The correlation suggests the mechanical connection between the two seismic regions, which belong to the same segment of the Pacific plate underthrusting at the northeastern Japan arc.View full abstractDownload PDF (829K) -
Yasuhiro UMEDA1975 Volume 28 Issue 3 Pages 313-320
Published: October 10, 1975
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSA temporary observation was carried out at Izu peninsula using a wide band (0.02-50Hz) seismograph system of portable type. Seismic waves observed at short focal distances (Δ≈10Km) were analysed for studying the source characteristics. The wide band seismograph system consisted of two electromagnetic vertical seismometers with natural periods of 1Hz and 0.2Hz, electrical R-C integrating circuits and a long term data recorder. Seven seismograms with good signal to noise ratio up to long period range were analysed by using an analogue type band-pass filter.
The displacement spectra thus evaluated were found not to have any flat portion at lower frequency, showing convex and concave shapes, corresponding frequencies varying systematically with magnitude of earthquake. Speaking generally, the frequencies corresponding to the concave and convex decreased with increasing magnitude in an observed range from 2.7 to 4.0. From this fact, the peculiar spectral structure may be closely related to some of the source parameters, that is, the portion of the spectral structure lower than the concave frequency represents the perpetual displacement caused by dislocation as usual, but the convex must arise from some resonance of the source region caused perhaps by relaxation process.View full abstractDownload PDF (3621K) -
Masakazu OHTAKE, Kazuo HAMADA1975 Volume 28 Issue 3 Pages 321-329
Published: October 10, 1975
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSVertical profile of hypocentral distribution of the Matsushiro earthquake swarm was minutely investigated based on a tripartite observation which was carried out in the swarm region.
Our observation confirmed that the seismic activity was almost restricted within a thin, 4km thick, layer and the uppermost 1km of the crust was completely aseismic throughout the swarm. We also found an upward migration of hypocenters with respect to time. From average velocity of the migration, 0.9×10-3km/day, intrinsic permeability of the medium was estimated at 20-90×10-9 darcy under the assumption that hypocentral distribution is an indicator of deviatric pressure of interstitial water.View full abstractDownload PDF (739K) -
Kazuo OIKE1975 Volume 28 Issue 3 Pages 331-346
Published: October 10, 1975
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSFive stations of the Tottori Microearthquake Observatory have supplied an amount of records of microearthquakes since June, 1965. They are very useful to investigate the characteristics of spatial and temporal distribution of microearthquakes. Using data from three stations MZT, OYT and IZT, a seismological bulletin has been compiled. It contains P, P-S and P-F times and directions of initial motions at three stations, the coordinates of foci calculated from data of three stations and magnitude of each shock determined from total duration (P-F time).
From June, 1965 to December, 1973, 7346 earthquake foci have been determined. Their epicenters have been plotted on seismicity maps. One of significant results from them is that the close relation between active faults and alignments of epicenters has been recognized.
Computed results of epicenters from data of the three stations have good accuracy comparing with those from five stations. Errors of hypocenters near to the network are less than 2km. Those of distant foci whose P-S times are larger than 10 seconds are less than 10km. Because of the important purpose to know the temporal distribution of microearthquakes, almost all data containing some reading values which do not have so good accuracy have been used for calculation.
Frequency distribution of magnitudes shows the normal activity in this region. It also shows that distant shocks whose magnitude are larger than 2.0 and epicentral distances are about 150km, are detected by this network of three stations. Hypocenters whose magnitudes are larger than 1.0 have been detected in the near region around the network.View full abstractDownload PDF (1313K) -
Katsuhiko ISHIBASHI1975 Volume 28 Issue 3 Pages 347-364
Published: October 10, 1975
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSFor the purpose of precise relocation of earthquakes which had occurred in Japan around the first quarter of this century, a computer program was written which calculates hypocenter parameters by the method of least squares using S-P times at more than three stations and employing an arbitrary multi-layered crustal structure.
As examples of relocation, about five semi-destructive earthquakes in the Kanto district: the Ryugasaki earthquake of 1921, the Yatabe earthquake of 1922, the Mitsukaido earthquake of 1923, the Uraga Channel earthquake of 1922 and the Haneda earthquake of 1926, all near-field S-P time data were carefully examined and hypocenters were redetermined. The epicenters and the focal depths obtained are expected to be uncertain by less than ±10km except the Uraga Channel earthquake. The former three, which has been suspected to be precursory activities of the Great Kanto earthquake of 1923, were ascertained to have their origins in the upper mantle beneath the SW part of the Ibaraki Prefecture where is even now a remarkable swarm area.View full abstractDownload PDF (1720K) -
Toshikatsu YOSHII1975 Volume 28 Issue 3 Pages 365-367
Published: October 10, 1975
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (395K) -
Kiyoshi ISHII1975 Volume 28 Issue 3 Pages 367-370
Published: October 10, 1975
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (453K) -
Ichiro KAYANO1975 Volume 28 Issue 3 Pages 370-372
Published: October 10, 1975
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (263K)
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