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Volume 35, Issue 3
Displaying 1-13 of 13 articles from this issue
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Kiyoshi ITO, Hiroshi MURAKAMI, Shoji HORIE, Yoshimi SASAKI, Shuzo ASAN ...1982 Volume 35 Issue 3 Pages 353-366
Published: September 25, 1982
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSA seismic refraction experiment was conducted in the northern part of Lake Biwa, Kinki District, Central Japan, in October, 1978. The purpose of the experiment was to know the thickness of the sedimentary layer beneath Lake Biwa, preparing for the boring project on paleolimnological study.
Four shots were detonated on land and fifteen seismometers were set at the bottom of the lake, along a profile of 34km long. By the analyses of the clear P wave onsets, the underground structure of Lake Biwa was obtained. The P wave velocity of the sedimentary layer varies from 1.5 to 2.0km/s, and it is assumed to be 1.8km/s in this study. The thickness of the sedimentary layer is 0.8km in the western part of the lake, decreasing towards northeast part with an inclination of 6-7 degrees. The basement layer has a velocity gradient, which has the P wave velocity of 5.0-5.2km/s near the upper boundary and the velocity gradient of 0.25km/s per 1km. Comparing this velocity increace with that from laboratory experiment on rocks, this velocity gradient in the basement layer is considered to show the in situ pressure effect.View full abstractDownload PDF (1153K) -
Akira IKAMI, Kiyoshi ITO, Yoshimi SASAKI, Shuzo ASANO1982 Volume 35 Issue 3 Pages 367-375
Published: September 25, 1982
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe crustal structure of Shikoku, Japan was studied by seismic refraction experiments which were carried out in March 1975. Thirteen temporary stations were aligned to the SW direction from off Sakaide to Cape Ashizuri, Shikoku. All of the stations were equipped with magnetic tape recording systems.
Two kinds of refracted waves with the apparent velocity of 6.05km/s and 7.8km/s were observed as first arrivals, although the seismograms were not of good quality. Certain secondary phases can be interpreted as refraction from the layer of 6.6km/s velocity.
Because of small number of data and of lack of reversed profile, only a rough picture on the crustal structure can be discussed in this paper. The superficial layer with a velocity of 5.5km/s becomes thin toward the southwest in Shikoku. This layer shows an abrupt change of its thickness at about 25km south of the Median Tectonic Line. The upper crustal structure with a velocity of 6.0km/s has an average thickness of about 20km. The velocity of the lower crust is assumed as 6.6km/s. The derived crustal structure is concordant with the structure of the eastern part of Shikoku derived from the Miboro and the Toyama explosions.View full abstractDownload PDF (820K) -
Kiyoshi ITO, Toshikatsu YOSHII, Shuzo ASANO, Yoshimi SASAKI, Akira IKA ...1982 Volume 35 Issue 3 Pages 377-391
Published: September 25, 1982
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSExplosion seismic observations were made for the investigation on the crustal structure of Shikoku along a profile in NE-SW direction crossing the Median Tectonic Line (MTL), one of the most pronounced tectonic lines in Japan. Seismic waves generated by the Iejima explosion of 3500kg in charge amount and the first Torigatayama explosion of 2400kg were observed at sixteen temporary stations in January, 1977 and those by the second Torigatayama explosion of 4100kg, at thirteen temporary stations in February, 1978. A detailed shallow velocity structure in relation to the MTL was obtained from clear refracted waves through the granitic layer. The first layer shows an abrupt change of its thickness at the MTL. The layer is about 4km thick to the northeast of the MTL, but it might almost disappear in the immediate southwest of the MTL. Apart from the MTL towards southwest it tends to thicken. The deeper structure up to the upper mantle was obtained by making use of clear later arrivals such as reflected and refracted waves besides a small number of first arrivals at long distances. The granitic layer with a velocity of 6.1km/s has an average thickness of about 20km and is underlained by the basaltic layer with a velocity of 6.7km/s. The velocity of the upper mantle is 7.8km/s and the depth of the Moho discontinuity is 30-35km.View full abstractDownload PDF (1281K) -
Isao YAMADA, Hideki MURAKAMI1982 Volume 35 Issue 3 Pages 393-400
Published: September 25, 1982
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSWe observed self-potential variations associated with quarry blasts. The amplitude of the observed self-potential across a pair of electrodes 20 to 50m apart is about 5-20mV in the distance range of 5-100m from the blast point. The variation of the self-potential began before the elastic wave arrival to the electrodes, and seem to have begun almost simultaneously with the rock blast. Later parts of the self-potential signals are very similar to those of the transverse components of seismic signals and indicate that the electric potential variation is induced by seismic-wave propagation, probably due to the electro-kinetic phenomena proposed by MIZUTANI et al. (1976), and experimentally studied by PARKHOMENKO (1964).
The cause of the earliest part of the self-potential variation is unknown. Since the present quarry blast is for shale and the site is highly wet, it is very unlikely for the piezo-electric effect to have caused such a large variation of electric potential field. The self-potential variation might be related to the phenomena such as tribo-electricity or charge separation on newly-created surfrces.
If the occurrence of self-potential variation associated with the present quarry blasts is generally true for any type of rock failure, the measurement of self-potentials on ground may yield a new tool for exploring a physical mechanism of natural earthquakes, as well as for determining the origin time of the earthquakes. Further field measurement and laboratory experiments are required to reveal the nature of the self-potential variation associated with rock failure.View full abstractDownload PDF (628K) -
Kazuo HAMADA, Masakazu OHTAKE, Yoshimitsu OKADA, Shozo MATSUMURA, Fumi ...1982 Volume 35 Issue 3 Pages 401-426
Published: September 25, 1982
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe National Research Center for Disaster Prevention (NRCDP) is constructing a large scale network for observation of microearthquakes and ground tilt in the Kanto-Tokai area, as a part of the national program of earthquake prediction. The number of observation stations, being 49 as of April 1982, will total 66 when the program is completed in fiscal 1983.
NRCDP started the construction of three deep borehole observatories in and around Tokyo in 1970, and the program was completed in 1980. Those deep borehole observatories are included in the new network of the Kanto-Tokai area together with other existing observation stations of NRCDP.
All data are transmitted through telephone lines to NRCDP in the Tsukuba Science City by the Pulse Code Modulation Method. Application of new techniques such as network timing synchronization and high density transmission of digital data distinguishes the present telemetry system from conventional ones.
Stress is put on data processing systems as a prediction-oriented system. A computer system which is directly connected to the telemetry system carries out the filing of records and monitoring of crustal activities on a real-time basis. Further steps of data processing including hypocenter determination by semi-automatic method are executed by another computer system. These systems enabled us to complete the daily routine of seismic data within a half day since it was observed.
Playing an important role in monitoring the crustal activity, the Kanto-Tokai network is offering the high quality data, which is useful for a variety of studies on earthquake prediction, especially those for the prediction of the impending Tokai earthquake.View full abstractDownload PDF (2435K) -
Takashi TADA1982 Volume 35 Issue 3 Pages 427-433
Published: September 25, 1982
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSAn anomalous crustal uplift was observed at the west coast of Boso Peninsula. The crustal uplift began at the same time as the mining of mountain rock which began about ten years ago.
It seems that the crustal uplift is the result of the elastic recovery deformation of the earth's crust caused by the man-made surface unloading.
An elastic modulus of the uppermost earth's crust estimated by the total amounts of crustal uplift and mined rock is about 1-2×1011dyne/cm2.View full abstractDownload PDF (733K) -
Tsuneo YAMAUCHI, Michikuni SHIMO1982 Volume 35 Issue 3 Pages 435-446
Published: September 25, 1982
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe concentration of 222Rn in air in the gallery at Mikawa. Crustal Movement Observatory (Toyohashi City, central Japan) has been continuously measured with a flow-type ionization chamber since April, 1977 for the investigation of pre-earthquake anomalies. The observed 222Rn concentration shows remarkable increase after rainfall. It seems that 222Rn rich air is squeezed in the gallery by the contractile force caused by rainfalls from faults with elevated 226Ra content. The variation of 222Rn concentration in the gallery has been calculated from the rainfall data from June, 1977 to December, 1979. Sometimes remarkable disagreements between the observed and calculated values of the 222Rn concentration are seen before and after the occurrence of nearby earthquakes. Such a disagreement might be a precursor of nearby earthquake. The concentration of 222Rn is also influenced by the changes in atomospheric pressure; it increases as the pressure drops and decreases as the pressure rises. Seasonal variations are recognized, too. Continuous observation of 222Rn has also been started in June, 1980 at Kikugawa Crustal Movement Observational Station (Shizuoka Prefecture, central Japan).View full abstractDownload PDF (1157K) -
Time Intervals of Successive EarthquakesToru OUCHI1982 Volume 35 Issue 3 Pages 447-460
Published: September 25, 1982
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSA new statistical model is presented for describing the frequency distribution of the time intervals between the successive earthquakes. In this modelling, we consider a general differential equation for the probability distribution function f (x) as
df(x)/dx=-g(x, f), (1)
where x is the time interval of the successive events. Assuming that the function g depends only on f and expanding g(f) with respects to f and neglecting higher terms than the second order, we obtain the following equation.
df(x)/dx=-β(1±αf)f, (2)
where α and β are constants. In the limit of α→0, we get the familiar exponential distribution. The general solution of this equation is given as
f(x)dx=1/exp[β(x+ξ)]±1 dx/α. (3)
This function form is equivalent to the familiar distributions known as the Bose-Einstein (-) and Fermi-Dirac (+) distribution in statistical physics. By using this model, the frequency distributions of the intervals of actual seismic series which deviate from the exponential distribution are successfully described. The result shows that the second term of the right side of ed. (2) which characterizes the clustering effect of the events is essentially important in the earthquake occurrences.View full abstractDownload PDF (1057K) -
Si-hua ZHENG, Ziro SUZUKI, Takeshi HASEGAWA1982 Volume 35 Issue 3 Pages 461-468
Published: September 25, 1982
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe previous paper [SUZUKI and HASEGAWA (1970)] discussed the stationary response of electromagnetic seismometer when its pick-up is shunted with a condenser to have a flat displacement response for longer period than the natural period of the pendulum. A general study on the transient response of the same system is made in this paper. Main effects of shunt condenser on the impulse response are: (i) The response is more likely to be oscillatory than the case without condenser. (ii) The period of oscillatory impulse response becomes longer. (iii) Statical magnification decreases. (iv) The time of the first peak of oscillatory impulse response is not zero but has a finite positive value. (v) The ratio of amplitudes of the negative overshoot and the first peak becomes large. Some of these effects imply a deterioration of transient response. The quantitative computation, however, shows that it is not so serious for many seismometer commonly used.View full abstractDownload PDF (618K) -
Satoshi MIURA, Hiroshi ISHII1982 Volume 35 Issue 3 Pages 469-471
Published: September 25, 1982
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (359K) -
Takeshi HASEGAWA1982 Volume 35 Issue 3 Pages 472-475
Published: September 25, 1982
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (479K) -
Akira IKAMI, Hiromi OHKUBO1982 Volume 35 Issue 3 Pages 475-478
Published: September 25, 1982
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (410K) -
Kiyoo MOGI1982 Volume 35 Issue 3 Pages 478-482
Published: September 25, 1982
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (521K)
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