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Volume 31, Issue 4
Displaying 1-9 of 9 articles from this issue
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In Cases Involving a Parameter c for the Maximum MagnitudeTokuji UTSU1978 Volume 31 Issue 4 Pages 367-382
Published: December 25, 1978
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSIn many cases, the log-frequency vs magnitude curves for earthquakes show considerable curvature, though the well-known G-R (Gutenberg-Richter) formula predicts a straight line. To represent such data, two modifications of the G-R formula have been proposed.
log n(M)=a-bM M≤c
n(M)=0 M>c} (2)
and log n(M)=a-bM+log(c-M) M<c
n(M)=0 M≥c} (3)
These are called here the truncated G-R formula and the modified G-R formula, respectively. These equations can be written in the form of probability density function:
f(x)=B/1-e-BCe-Bx C≥x≥0 (5)
f(x)=B2/e-BC+BC-1e-Bx(C-x) C>x≥0 (6)
where x=M-MS, B=b ln 10, C=c-MS, and MS is the lower limit of magnitude above which the data is complete.
The estimation of B and C in equation (5) by the method of moments was discussed by Okada (1970) and Cosentino et al. (1977). The equations proposed here are
expC(C-2x)/Cx-x2=C2-2Cx-x2/2x2-x2 (16)
B=(2x-C)/(x2-Cx) (15)
or x2/x2=2-BC(BC+2)/(eBC-1)/1-BC/(eBC-1) (18)
Bx=1-BC/(eBC-1) (19)
The maximum likelihood method for equation (5) yields only one equation (equation (19), Page (1968), Okada (1970)). If we adopt C=Max(xi) as the second equation, the C value is considerably biased. To correct the bias, a correction ΔC which is a function of B and C is proposed. For this correction we must use some estimated values for B and C.
To estimate B and C in equation (6) by the method of moments the following equations are used.
x2/x2(e-BC+BC-1){e-BC(B2C2+4BC+6)+2BC-6}/{e-BC(BC+2)+BC-2}2 (25)
Bx=e-BC(BC+2)+BC-2/e-BC+BC-1 (23)
The maximum likelihood estimates of B and C in equation (6) can be obtained by the equation:
2-Bx=C/S ∑Si=1 1/C-xi=BC(1-e-BC)/e-BC+BC-1 (27), (29)
The accuracy of B and C values determined by the above methods is estimated by Monte Carlo technique for the cases of S=50, 100, 200, 400, and 800 and several values of B and C. If we adopt the truncated G-R formula, the second method (which uses C=Max(xi)+ΔC) gives more accurate C values, whereas the accuracy of B values is almost the same as that obtained by the method of moments. If we adopt the modified G-R formula, the maximum likelihood method gives more accurate B and C values than the method of moments. The η value (η=x2/x2) is a useful index for the deviation of the distribution of data from the G-R formula (for the G-R formula, theoretical value for η is 2). An application of the present methods shows regional variations in b, c, and η values of shallow earthquakes in Japan.View full abstractDownload PDF (1213K) -
Tokutaro HATORI1978 Volume 31 Issue 4 Pages 383-389
Published: December 25, 1978
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSFor the tsunamis generated near Japan and the circum-Pacific seismic zone during the last 26 years (1952-1977), the result of tsunami warning which is reported by the Japan Meteorological Agency is investigated, comparing tsunami prediction with the actual values observed by tide stations. In the East Japan, tsunami warning gave 10min or more before the tsuami arrival time. However, in the West Japan and the Japan Sea side, a few tsunami warnings were forestalled, because the arrival times were only several minutes. Height predictions of most tsunamis were successful, but some relatively large tsunamis were underestimated. To be a successful tsunami warning requires not only the information of earthquake magnitude, but also the parameters of the spectra of seismic waves or earthquake moment.
The warnings of distant tsunamis observed in Japan have been successful except the 1952 Kamchatka and 1960 Chile tsunamis. In future, it must be on the watch for large earthquake occurring in these regions.View full abstractDownload PDF (607K) -
Tsuyoshi KANEMA, Itaru MAEDA1978 Volume 31 Issue 4 Pages 391-400
Published: December 25, 1978
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSMicro shocks produced by heating of the granit samples up to 750°C are observed. These shocks are grouped into three classes according to their amplitudes. The emission rates of these shocks belong to each classes are recorded as a function of the temperature and the heating rate, that is 23.3°C/min, 3.3°C/min, and 0.83°C/min. These amplitude ranges expressed by the out put voltage of the piezoelectric transducer are 1mV to 7mV, 7mV to 35mV, and above 35mV. The emission rate of the small to middle amplitude classes of shocks (up to 35mV) as a function of temperature has two maxima at about 550-600°C and 650°C. The emission rate of the largest amplitude class of shocks (above 35mV) decreases as the heating rate decreases.
The mechanisms of the largest amplitude class of shocks and the two maxima of the emission rate are discussed. The mechanisms discussed in this paper are as follows;
(1) The thermal stress produced by the thermal gradient over the sample.
(2) The stress produced by the difference or the directional inhomogeneity of the thermal expantion between constituent minerals.
(3) The stress concentration at crack tips when heat flows across crack surfaces.
Comparing the stress intensity factors for these mechanisms and taking the features of occurence of shocks into account, it is concluded that the maximum emission rate of shocks at about 550-600°C results from the mechanism of (3) and that about 650°C, from the mechanism of (2). The largest amplitude class of shocks results from the mechanism of (1).
Granit sample is fractured completely when the mean thermal gradient beyond about 90°C/cm.View full abstractDownload PDF (4933K) -
Itaru MAEDA, Yoshinobu MOTOYA, Sadaomi SUZUKI1978 Volume 31 Issue 4 Pages 401-413
Published: December 25, 1978
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe processing system of earthquakes and earth strain data telemetered at Hokkaido university is reported. This system consists of the data recording system, the reproducing system, and the analyzing system.
The data are continuously recorded all time on high density digital magnetic tape recorder. The data are reproduced in two form. One is in analogue form and the other is in computer readable digital one.
For the processing of data three kinds of program groups have been developed. The first group has a function which copies data from an original tape to a compile tape. The second group has functions which are phase readings, earthquake origin calculations, filings, and map displays. These are used for routine works. Functions of third group are data I/O handlings, analyses of digital data, and outputs of results on the graphic display or LP.
In this report, all functions and merits or demerits of this system are discussed in some details.View full abstractDownload PDF (1180K) -
Hiroaki TSUKAHARA, Ryuji IKEDA, Hiroshi SATAKE, Masakazu OHTAKE, Hiros ...1978 Volume 31 Issue 4 Pages 415-433
Published: December 25, 1978
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSWe succeeded in an in situ measurement of the crustal stress by using the hydrofracturing method for the first time in Japan. It also was the first time in Japan that crustal stress measurements were made for the purpose of earthquake prediction studies.
Main parts of field experiments are to pump water into a selected interval of a measurement borehole, and to fracture the side wall of the hole by hydraulic pressure. A pair of “inflatable packers” is used to seal the interval. After the packers are recovered, the inclinations and azimuths of new fractures are observed with a “borehole televiewer”. The horizontal principal stresses and their directions are calculated from the records of pressure change and the fracture azimuth. Measurements were carried out in two boreholes 100m deep at Katsurajima and Miyajima in Okabe Town, Shizuoka Prefecture in Feb. -Mar., 1978. In the Katsurajima well, four measurements were made at depths between 57 and 100m and two sets of hydrofracturing data were obtained. In the Miyajima well three measurements were made at depths between 80 and 90m with satisfactory results.
The minimum and maximum horizontal compressive stresses at those experimental sites are calculated to be 32 to 53 bar and 58 to 79 bar, respectively. The stresses increase in proportion to the depth. All of the calculated horizontal stresses are greater than estimated vertical stresses due to overburden weight so that the least principal stress is vertical. The direction of the maximum compression was found to be N 40°E from televiewer observation of a new fracture at the 95m-depth. This direction is not in agreement with the regional strain field obtained from geodetic survey. On the other hand, earthquake mechanism studies suggest a complicated feature of the stress field in this area.
Further, relations between fracture toughness and depths of radial cracks on borehole walls are derived from the hydrofracturing data. The depths of pre-existing cracks on the borehole walls at the test sites are estimated to be several mm from the relation.
This experiment reveals that the hydrofracturing method is successfully applied to such an active and complicated orogenic zone as the Japanese islands. However, the investigation on the relation among the geodetic and seismic data and the in situ stress values is the subject for a future study.View full abstractDownload PDF (4900K) -
Ryuji IKEDA, Hiroaki TSUKAHARA, Hiroshi SATAKE, Masakazu OHTAKE, Hiros ...1978 Volume 31 Issue 4 Pages 435-444
Published: December 25, 1978
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDuring the hydrofracturing experiments of the base rocks at Okabe Town, Shizuoka Prefecture, highly sensitive observations of the Acoustic Emissions (AE) were carried out in order to study the fracturing mechanism. A hydrophone, piezoelectric accelerometers and seismometers were used for the observations. A number of AE was observed by the hydrophone placed at the depth of 10m in the boreholes. The results of the observation revealed the following characteristics of the AE, (1) predominant frequency of the initial motions is about 5kHz and that of maximum amplitude is about 1.5-2kHz, (2) wave-form of the initial motions is very sharp and pulse-like, (3) the AEs are initiated a few seconds after the starting of the increase in water pressure, and (4) number of the AE is closely related to the pressure variation.
These characteristics demonstrate that those AEs are caused by the hydrofracturing of the rocks. It is expected that extensive observations of the AE provide valuable data for the identification of the critical fracturing pressure, and for the basic investigation of the fracturing phenomena.View full abstractDownload PDF (991K) -
(II) Crustal MovementsYoichiro KOMUKAI, Hiroshi ISHII1978 Volume 31 Issue 4 Pages 445-455
Published: December 25, 1978
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSCrustal movements in the Tohoku district (northeastern Honshu) are observed now by the eleven stations operated by Tohoku University.
Detectabilities of strain- and tilt-steps by the observation net of Tohoku University are investigated for earthquakes with various magnitudes occurring in and around the Tohoku district.
Contour maps of estimated detectability in strain- and tilt-steps are calculated and plotted for earthquakes with various magnitudes.
It is found that an area detected by the observation net is wider for strain components than for tilt components.
It is shown that observation stations for crustal movements can observe strain-steps for earthquakes with magnitude larger than 7, happened at the western side of Japan trench.View full abstractDownload PDF (1209K) -
Tomeo NAGAMUNE1978 Volume 31 Issue 4 Pages 457-467
Published: December 25, 1978
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe natures of multiple earthquake are investigated in relation to the tectonic structure in the source region. The multiple earthquake is characterized by the successive different events that occurred at respective places in the source region. However, it shows an apperance of one earthquake in the seismogram, and does not give an impression of two earthquakes or more.
It seems that the earthquake multiplicity at the source is attributed to the complexity of tectonic structure in the source region, as it consists of blocks, and that the 2nd and later events take place near boundaries of blocks, due to the extending of rupture to the next block.View full abstractDownload PDF (1072K) -
The Tokachi-oki Earthquake of March 4, 1952Mamoru KATSUMATA1978 Volume 31 Issue 4 Pages 469-470
Published: December 25, 1978
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (255K)
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