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Yukio HAGIWARA, Hirokazu TAJZMA, Sadakatu IZUTUXA, Hideo HANADA
1976 Volume 22 Issue 4 Pages
201-209
Published: March 25, 1977
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A remarkable crustal uplift covering an area of about 30 km across was found by leveling resurveys over earthquake swarm epicenters in the eastern part of Izu Peninsula . The top of the uplift has amounted to 15 cm during the period of 1969-1976 . The repeatedly-made precise gravity surveys also detected gravity decrease with a rate of about 3 μgals/cm, i.e., the free-air rate, which can be interpreted as a dilatancy generation in the crust. The gravity-decreasing area has been gradually extended in a N-S direction. This fact may indicate the dilatancy diffusion due to the compression by a continuous westward motion of the Philippine Sea plate.
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Shigeyasu ONO
1976 Volume 22 Issue 4 Pages
210-222
Published: March 25, 1977
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The distribution of gravity stations and their number, designed to give an adequate accuracy in gravimetric deflections of the vertical is considered. The method can be applied to determination of the number and distribution of gravity stations which yield results of accuracy adequate for the purpose of carrying out astrogravimetric leveling . The accuracy of astrogravimetric leveling is estimated that depends on the error of astrogeodetic gravimetric deflections of the vertical determined from the variations of differences between the gravimetric and astrogeodetic deflections of the vertical at adjacent astronomical stations. The accuracy required for astrogravimetric leveling is determined from the point of view of spatial constituting and rigorous computing the astrogeodetic network. Practical problems connected with forming an astrogravimetric leveling system are discussed.
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Keichi KASAHARA, Ichiro NAKAGAWA, Takehisa HARADA
1976 Volume 22 Issue 4 Pages
227
Published: March 25, 1977
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Takehisa HARADA
1976 Volume 22 Issue 4 Pages
228-234
Published: March 25, 1977
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This report is a short guide to geodetic data accumulated in the Geographical Survey Institute in Japan for researchers who want to utilize them.
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Kennosuke HOSOYAMA
1976 Volume 22 Issue 4 Pages
235-241
Published: March 25, 1977
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An estimation of observational accuracy of crustal movement is usually difficult . Particularly, in the case of continuous observations of the crustal movement, it needs extraordinary efforts to detect the original crustal movement from composite signals of original, instrumental, meteorological etc . in the record. In this paper, some discussions are made for necessary conditions to estimate the observational accuracy and possibility of detecting the extensive crustal movement . The project of precise observations of crustal movement at a new planning station is also proposed.
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Takeshi DAMBARA
1976 Volume 22 Issue 4 Pages
242-251
Published: March 25, 1977
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First, a precise definition is made for crustal movements which include all sorts of movements detected by continuous (CTCM), tidal (TDCM), geodetic (GDCM), topographic (TPCM) and geological (GLCM) observations. Sometimes there are difficult problems of inconsistency in the comparison of the observations by different methods of crustal movements. As a preparation to discuss these problems, leading ideas I, II and III are proposed. Next, a problem of consistency in accuracy between the five sorts of crustal movements is discussed, where the synthetic accuracy of instruments and time are considered, and the accuracy of geodetic movement is chosen as a standard .
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Tokihiko MATSUDA
1976 Volume 22 Issue 4 Pages
252-263
Published: March 25, 1977
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Recent geologic crustal movement in Japan can be assumed to have proceeded uniformly during at least the last a few hundred thousand years. The average rate of movement during this period is of the order of millimeters per year in Cenozoic active zones. This rate of movement is one order higher than that during Neogene and is nearly the same as that during historical times. A comparison of historical crustal movements with geologic ones shows that in the focal region a co-earthquake crustal movement is always consistent in sense with geologic crustal movements, but outside the focal region it is not necessarily consistent. Generally, an integral sum of crustal movements during the period of an earthquake cycle is consistent in sense with the recent geologic crustal movement in the respective area. In strike-slip faulting, however, the sense of the subordinate vertical component of fault displacement and the associated vertical deformation along strike-slip faults is not always cumulative through time even in the focal region.
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Atsushi TSUCHIYA
1976 Volume 22 Issue 4 Pages
264-274
Published: March 25, 1977
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Accuracies of Doppler satellite tracking, satellite and lunar laser rangings and the very long baseline interferometer (VLBI) for geodetic applications are discussed from the practical point of view . As two radio waves at two operating frequencies pass through different regions in the ionosphere due to the difference in refractive indices, for the Doppler satellite system, error is caused, especially at lower satellite angles of elevation and limits accuracy . An accuracy of 10 cm will be practically obtained by laser ranging and VLBI . To improve the accuracy to 1 cm, much effort is necessary, i.e., the development of short pulse laser, high speed electronics, accurate retro-reflectors for laser ranging; and for VLBI, the ionospheric and atmospheric effects should be studied more carefully and the limitation of SN in the receiving system should be overcome .
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Tohoku University
1976 Volume 22 Issue 4 Pages
275-277
Published: March 25, 1977
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Strain accumulation in the Tohoku District is revealed by analyzing data of extensometers observed in array stations. It is shown that feature of the principal strain coincides with the results obtained from earthquake mechanism. It is found that maximum shear strain migrates in the N 50°W direction with the velocity 40 km/year.
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Toshihiro KAKIMI, Yoshihiro KINUGASA
1976 Volume 22 Issue 4 Pages
278-279
Published: March 25, 1977
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Hiroshi SATO
1976 Volume 22 Issue 4 Pages
280-281
Published: March 25, 1977
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Izuo OZAWA
1976 Volume 22 Issue 4 Pages
282-283
Published: March 25, 1977
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According to data of the precise leveling around Lake Biwa-ko and the continuous observation of the Crustal deformation in old Osakayama tunnel which is located in the south-west district of the lake, the earth crust of the north-west district of the lake has upheaved recently. The study of the crustal movement around the lake is performed by the continuous observation of the crustal deformation in the tunnel, precise leveling around the lake and measurements of the lake water level.
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Kazuo OIKE, Yoshimichi KISHIMOTO, Kajuro NAKAMURA, Yoshiro NAKAHORI
1976 Volume 22 Issue 4 Pages
284-285
Published: March 25, 1977
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Data from continuous observation of crustal movements by an array of extensometers crossing the fractured zone of the Yamasaki fault have been analyzed. The fractured zone shows significant movements after isolated heavy rainfall, and a few days after such rainfall microearthquake swarms occur along this active fault. We suggest that the rainfall triggers the occurrence of earthquakes.
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Hiroshi TAKAHASHI, Teiji KUMAGAI, Norio OYAGI
1976 Volume 22 Issue 4 Pages
286-287
Published: March 25, 1977
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Tadanao OHISHI, Shoichi SEINO, Yoshimasa SAKURAI
1976 Volume 22 Issue 4 Pages
288-289
Published: March 25, 1977
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Crustal Dynamics Division, Geographical Survey Ins
1976 Volume 22 Issue 4 Pages
290-291
Published: March 25, 1977
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Minoru KASAHARA
1976 Volume 22 Issue 4 Pages
292-294
Published: March 25, 1977
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Earthquake prediction research project began in earnest in Hokkaido University when the Urakawa Seismological Observatory (KMU) was established in 1967. Later the project has been gradually advanced so that the Erimo Geophysical Observatory (ERM) and the Sapporo Seismological Observatory (HSS) in turn were established in 1971 and 1973, respectively. In order to accelerate the project development, the Research Center for Earthquake Prediction was established in 1976 in the campus of Hokkaido University. The Research Center provides us with efficient data collection by the use of telemetry and speedy data analysis by a computer. In this report, a data collection system using time-sharing multichannel digital PCM telemetering is briefly described.
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Tsuneo YAMAUCHI
1976 Volume 22 Issue 4 Pages
295-296
Published: March 25, 1977
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Izuo OZAWA
1976 Volume 22 Issue 4 Pages
297-298
Published: March 25, 1977
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In order to determine information relating to large earthquakes from crustal deformation at a distance of 100 km, for example, we need to observe strains as small as 10
-7. The surface and the crust are formed of many blocks which have individual elastic and plastic coefficients. Therefore, a complex pattern of strain is usually observed near the surface even under a uniformstress pattern. Besides, changes of creep velocity, viscosity and strength of the crust forming materials depending on temperature, watersaturation and pressure are much larger than those of elasticity. Therefore, the gradient of distribution of the plastic deformation is usually complex and large. The short period strains caused by seismic waves, the earth tidal force and so on chiefly consist of elastic deformation, but the long period crustal movement consists both of elastic and plastic deformations. In addition, the stress caused by atmospheric phenomena is very complex at shallow depths. So, the pattern of the long period strains is more complex than that of the short period strain near the surface. In order to avoid the trouble produced by the complexity of the ground structure and the ground noise on observation of crustal deformation, we require placing the instrument in a deep place. However, increase of efficiency of the station decreases rapidly with depths. There are two methods to offset the ground noise and to smooth the irregularity. The first method is group setting, in other word; array, which takes the average of observations of the same component at several observatories distributed in a specified area whose radius is smallerthan few kilometers. The second method is the using of a long base line with a length longer than few hundred meters. An experiment to determine the relativemerit between these two methods was conducted at old Osakayama tunnel of the former Tokaido Line.
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Hiroshi ISHII
1976 Volume 22 Issue 4 Pages
299-301
Published: March 25, 1977
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A prediction method is applied to the analysis of crustal movement in order to find anomalous phenomena preceding earthquakes. It is found that the technique is useful from the results employed for some cases.
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Teruyuki KATO
1976 Volume 22 Issue 4 Pages
302-304
Published: March 25, 1977
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Yoshimitsu OKADA, Keichi KASAHARA
1976 Volume 22 Issue 4 Pages
305-307
Published: March 25, 1977
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A program system, which uses a TSS (Time-Sharing System) data terminal and files of crustal movement data, has been studied. The present paper describes the first part of the system, which is linked to the store-forward data trans fer system at crustal movement observatories [1] and processes their tilt- and strain-meter records on a routine basis. The advantages of the present system may be emphasized as follows: (1) Easy operation aided by semiautomatic and conversational mode processing. (2) Protection of the filed data against careless operation. (3) Economical use of the limited file space. (4) Adaptability for further development of the system.
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Yoichiro FUJII
1976 Volume 22 Issue 4 Pages
308-310
Published: March 25, 1977
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FUJITA and FUJII proposed detailed phases of seismic Crustal movement in 1973 [1]. The α phase is stationary crustal movement. Anom alous crustal movement β phase prior to an earthquake occurrence is divided into two phases β
1 and β
2. β
1 phase is beginning of precursory crustal movement and β
2 phase is the following unstable crustal movement. Co-seismic crustal movement γ phase is divided into three phases γ
1, γ
2 and γ
3. γ
1 phase is just forerunning preslip and γ
2 phase is co-slip closely associated with earthquake occurrence. γ
8 phase is postslip, δ phase is transient one to the next aphase. Recently a creep dislocation model that assumes slow faulting movement along an extension of co-seismic fault plane was discussed in order to make a picture of anomalous crustal movement prior to earthquakes (for example, [2, 3]). The terminology "creep instability model" is used by MORTENSEN and JOHNSTONE [4]. In case of the 1964 Niigata earthquake, an abnormal upheaval was detected along the level-line across the epicentral region during the first period from 1955 to 1959. During the second period from 1959 to 1961, the northern part of the levelline subsided and the southern part upheaved continually [5]. These facts may be interpreted by assuming slow faulting at depth. The 1973 Nemurohanto-oki earthquake was also preceeded by anomalous crustal movement and associated gravity change during coand post-seismic periods. The author applies a creep dislocation model to interpret the associated gravity change.
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Yutaka TANAKA, Isao NAITO
1976 Volume 22 Issue 4 Pages
311-313
Published: March 25, 1977
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Ietsune TSUBOKAWA
1976 Volume 22 Issue 4 Pages
314-316
Published: March 25, 1977
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In 1969, the writer proposed the following equation for precursor time T for an earthquake of magnitude M.log T=0.79M-4.44.He also presumed that NT=10 in the Japan seismic area, where Ndenotes annual frequency of earthquake of magnitude M as specified in the equation. In the present paper, the writer confirmed these relations using the data in the Seismological Bulletin of the Japan Meteoro logical Agency (1926-1975). He also applied this equation for materials for history of Nankai and Tokai huge earthquakes and presumed that energy accumulation is continuous for a huge earthquake.
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Tsuneji RIKITAKE
1976 Volume 22 Issue 4 Pages
317
Published: March 25, 1977
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Statistics of recurrence time of great earth quakes at the Pacific subduction margins are made. The mean return period of great earth quakes is different from zone to zone ranging from 27 to 117 years. The standard deviation of the return period proves very small, several years say, in some cases. The probabilities for a great earthquake to recur in each zone are estimated on the basis of Weibull distribution analysis. The mean return periods thus estimated are combined with the relative plate velocities at respective zones in order to estimate the ultimate displacement at rupture at the interface of the continental plate and the downgoing oceanic plate. It is presumed that great earthquakes at subduction zones occur as a result of the rebound of the continental plate at the time of rupture. The ultimate displacement thus estimated ranges from 2 to 8 m, and seemssomewhat larger than that estimated on the basis of seismic observations although the value of ultimate displacement seems to harmonize roughly with estimates based on geodetic observations on land. However, the ultimate displacement at the Aleutian-Alaska zone as estimated here seems much smaller than that estimatedfrom actual observations. The ultimate strains, which are deduced from the displacements obtained on the assumption that the logarithmic extent of the deformed area is proportional to earthquake magnitude, are then calculated, and compared to thoseestimated for large inland earthquakes as revealed by repetition of geodetic surveys. The mean ultimate strain is estimated as 4.3 ×10
-5 for subduction zone earthquakes while that for inland earthquakes has been estimated as 4.7 ×10
-5. As the agreement between both the ultimate strains is fairly good, it is tentatively concluded that the strength of the continental-oceanic plate interface is similar to that as continental crust.
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“Future Scope of Research on Crustal Movement”
1976 Volume 22 Issue 4 Pages
319-325
Published: March 25, 1977
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