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Volume 42, Issue 3
Displaying 1-14 of 14 articles from this issue
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Hideo WATANABE1989 Volume 42 Issue 3 Pages 271-276
Published: September 24, 1989
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThis is the report of the study continued after §4 of the first report [WATANABE (1987)].
In general, the equation on tsunami magnitude is expressed as, Mt-logH-5.80=alogΔ+b, where H is maximum semi-amplitude of tsunami in meter, Δ traveling distance of tsunami in kilomeler, “a” the coefficient related to traveling distance of tsunami and “b” the one non-related to traveling distance of tsunami. If a=1 and b=0, Mt is the tsunami magnitude defined by ABE (1981).
In this paper, the values of “a” have been calculated by data of more tidal records than the ones of the first report. In case of near tsunamis occurred around the Japan Islands, the mean values of “a” is 0.74 in the Pacific coast of Hokkaido, 1.13 in Hakodate to the Sanriku coast of northeast Japan and 0.90 in the Pacific coast of southwest Japan. However, in case of distant tsunamis observed along the coast of the Japan Islands, it does not differ in three domains. It mean that a locality on tsunami propagation occurs only on near tsunamis.
Some considerations are taken as the difference of locality in case of near tsunami. As the result it is suggested that the effect of sea current is small and ones of sea depth and the propagation direction are large.View full abstractDownload PDF (640K) -
Seiji TSUBOI, Kazuki KOKETSU, Kiyoshi TAKANO, Takashi MIYATAKE, Katsuy ...1989 Volume 42 Issue 3 Pages 277-284
Published: September 24, 1989
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe Earthquake Prediction Data Center (EPDC) of the Earthquake Research Institute, University of Tokyo, has been receiving the hypocentral parameters and arrival time data acquired through the University Information System for Earthquake Prediction Research, which is operated by Japanese national universities under the national program for earthquake prediction. Through the cooperation of these universities, the data and hypocenters were compiled and stored in the database system of the EPDC. There are two types of database; one is the real-time database and the other is the revised database which is sent by magnetic tapes from each regional center. EPDC has prepared to open these database for every seismologists to use and now the real-time database can be used by the real-time monitoring system and the revised database is open to be public as the Japan University Network Earthquake Catalog. The hypocentral coordinates and orgin times listed in the catalog are redetermined by EPDC using the arrival time data of the revised database. Although, the minimun magnitude of the earthquakes listed in the catalog is 2.0, the earthquakes listed in the catalog covers the microearthquake activities in Japan. In the present paper, we discuss the hypocenter determination procedure of the catalog and also the characteristics of the hypocenters listed in the catalog.View full abstractDownload PDF (848K) -
Tamao SATO, Kazuaki MIURA, Yoshihiko KOBAYASHI1989 Volume 42 Issue 3 Pages 285-298
Published: September 24, 1989
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSTeleseismic travel times of P waves to northeastern Japan, in the distance range from 24° to 85°, have been studied using data from 19 high-sensitivity stations of the micro-earthquake observing network operated by the universities. About 2, 800 arrival times from 267 seismic sources were used. Most of the seismic sources are earthquakes in the subduction zones of the western Pacific and the Southeast Asia. Mean travel times calculated for data at 2° intervals were fitted by a polynomial to determine a mean travel time curve. The standard deviations of travel times at the intervals are on the average about 0.7s. Travel times from two Nevada Test Site explosions have been utilized to estimate a correction of -2.39s for the absolute level of the travel time curve. The shape of the travel time curve shows broad agreement with the result of other works (e. g. HERRIN et al., 1968), though it is characterized by earlier times around 30°, which is probably due to the effect of the subdcting plates beneath the Japanese Islands. Differences from the mean travel time curve are 2 seconds at maximum, and mostly range within 1 second. Clearly they depend on the azimuth, suggesting the lateral heterogeneity in the lower mantle and/or the upper mantle in the source region. For a group of sources in a small limitted area, the standard deviation of travel times reduces to a value less than 0.5s. Especially the travel times from 12 Kazakh nuclear explosions, whose epicenters are probably limitted within 10km, give a standard deviation of 0.18s. This is as small as that expected from the reading error of P phases for teleseismic events.
The relative travel-time residuals of each station are consistent with both the station corrections determined from an inversion of P-wave travel times from local earthquakes and the Moho time terms derived from a set of Pn phases from events in northeastern Japan. Therefore the relative travel-time residuals for the teleseismic events are estimated to be affected mainly by the inhomogeneity in the crust and the uppermost mantle beneath the station network.View full abstractDownload PDF (1590K) -
Ikuo KATSURA, Setsuro NAKAO, Yoshimichi KISHIMOTO, Takuo SHIBUTANI, Ka ...1989 Volume 42 Issue 3 Pages 299-310
Published: September 24, 1989
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe measurement of γ-ray count rate is continued at an observation vault of the Tottori Microearthquake Observatory since August, 1983. The method is by a γ-ray scintillation survey meter with an NaI (T1) scintillator. The result reveals an annual variation of γ-ray count rate as high in summer and low in winter. The annual variation seems to be related on the annual variations of atmospheric pressure as negative and of atmospheric temperature as positive. These relations, however, are held on the manner that the phase of γ-ray variation is faster than those of the meteorological factors; i. e. about 24 and 44 days faster than the atmospheric pressure and the temperature, respectively. The annual variation of γ-ray could be attributed to the regionally thermal deformation of crustal rocks. On the contrary, short term variations of the γ-ray count rate can be correlated with the atmospheric pressure and the temperature as about 4 days to 2 weeks periods. The daily variation which can be correlated with the daily variation of temperature is mainly observed at the fine days under a high atmospheric pressure in the spring season.
The simultaneously continuous measurement of γ-ray using a multichannel spectrometer with an NaI (T1) scintillator showed that the sources of γ-ray were 214Bi, 214Pb and 40K. The above-mentioned variations of γ-ray count rate can be attributed to the variation of gaseous radon concentration as 222Rn of uranium series in the soil gas at the vault.View full abstractDownload PDF (1082K) -
Fumiaki KIMATA, Yonezou ANDOU, Shouzou AOYAMA, Takanori OBATA, Kyouzou ...1989 Volume 42 Issue 3 Pages 311-316
Published: September 24, 1989
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSPrecise levelings across the Atera fault have been repeated every summer at Sakasita, Gifu-Prefecture since 1976. The leveling network consists of two loops with lengths of 1.3km and 2.6km. Loop closures of leveling were within 1.4mm. Geodetic tilt vectors are calculated from horizontal positions and annual elevation changes at bench marks by least squares method. If a residual of elevation change greater than the twice the standard deviation of the tilt vector is found at any bench mark, the calulation is repeated excluding the erroneous data. Significant ground tilts are observed four times, i. e., 1976-1977, 1981-1982, 1982-1983 and 1985-1986, and these tilt rates are 1.0-2.0μrad/y. Atera fault is geologically characterized by the uplift on the northeast side. However the present movement suggests northeast tilting during three epochs and southwest tilting at one epoch. The 1985 survey suggests that the western Nagano Prefecture Earthquake (ML=6.8; Sept. 14, 1984) about 30km to the north, caused co-seismic tilt of the ground.View full abstractDownload PDF (680K) -
Satoshi MATSUMOTO, Akira HASEGAWA1989 Volume 42 Issue 3 Pages 317-324
Published: September 24, 1989
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSWe have carried out a seismic refraction experiment around Bandai volcanic area, the southern part of Tohoku, by using a large capacity marine airgun. Analysis of observed seismograms from the airgun shots shows that the coda wave amplitude at each observation site is independent of hypocentral distance. This indicates that the coda wave energy is homogeneously distributed in the medium beneath the refraction profile. The coda wave amplitude correlates well to the amplitude of the direct P wave from distant earthquakes and inversely correlates to the Bouguer anomaly. The relative site amplification of the coda wave is nearly the same as that of the direct P wave, and is considered to be related to the average density or the thickness of sedimentary layer just beneath the observation site. By using the coda wave amplitude at each observation site, we can evaluate the relative site amplification. Correction of the site amplification factor gives a smooth and less scattered distribution of the P wave amplitude from the airgun shots along the refraction profile.View full abstractDownload PDF (761K) -
Kazuki KOKETSU1989 Volume 42 Issue 3 Pages 325-331
Published: September 24, 1989
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSSome techniques used in statistics, such as the variable change method, the penalty function method and the gradient projection method, are introduced to determine the location of a hypocenter with a definitely non-negative depth. Numerical simulations are carried out to compare the efficiency of them by using synthetic arrival time data for a four-station seismic array. They demonstrate that the penalty function method with a proper weight is the most efficient. However, if we take an improper weight, it may lead to a negative depth or an invalid solution. Since the variable change method and the gradient projection method do not have such arbitrariness, those can be implemented more easily into hypocenter determination processes operated routinely. The demonstration with real arrival time data shows that the variable change method as z=h2 has practical efficiency.View full abstractDownload PDF (755K) -
Hitoshi ODA1989 Volume 42 Issue 3 Pages 333-339
Published: September 24, 1989
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSWe have reexamined whether the velocity decrease of the seismic waves due to dilatancy can be detected or not. A numerical investigation was made to see the change of travel times by using synthetic seismograms of P-waves traveling through a dilatant region. In synthesizing the seismograms, the Brune's source model was used, and the P-wave velocity was assumed to increase with increasing frequency and to approach asymptotically an intrinsic velocity. This relation between P-wave velocity and frequency is based on the experimental result obtained by uniaxial compression test of a granitic rock sample; the velocity decrease is larger at low frequencies than at high frequencies. The dispersion curve is characterized by crack density ε, crack width 2a and intrinsic velocity α. A characteristic frequency fM=5α/πa, above which no velocity decrease is found, is defined. We investigated the change of the P-arrival times in the synthetic seismograms, changing both crack density and crack width. When the P-wave forms of earthquakes with the same magnitudes are recorded without off scale, the travel time anomaly can be detected in the case of fc<<fM, where fc is the corner frequency of seismic source spectrum. Therefore, for detecting the travel time anomaly, it is necessary to observe earthquakes in low frequency range of f<<fM, where the significant velocity decrease is expected. For this purpose, group arrival times of the P-wave at low frequencies may also be useful.View full abstractDownload PDF (794K) -
Ikuo KATSURA, Yoshihisa YAMADA, Susumu NISHIMURA, Tohru MOGI, Jun'ichi ...1989 Volume 42 Issue 3 Pages 341-348
Published: September 24, 1989
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSGeophysical surveys were carried out to trace the fracture zones in the Awakura and the Ute areas, the northeastern part of Okayama Prefecture, which borders on Tottori and Hyogo Prefectures. The Yamasaki fault terminates in these areas. The methods employed were ELF-magnetotelluric sounding and γ-ray survey. The trends of low resistivity zones were deduced from the principal axis directions of impedance tensor. The peak positions of γ-ray count rate suggest the location of fault lines at the surface layer. The traces of faults were estimated from the results of the surveys combining with the topographic lineaments. The estimated traces show that the Yamasaki fault sprays westward into several branches. A north-south striking fracture, which is tentatively named the Ute fault, is also estimated along the west side of the Kajinami River in Katsuta-cho. The northern extension of the Ute fault is considered to be linked with the linear array of epicenters between Tottori and Chizu. The Ute fault is a candidate for the boundary of tectonic blocks dividing the Chugoku and the Kinki districts.View full abstractDownload PDF (1396K) -
Masayuki TAKEMURA, Shigeto HIEHATA, Tomonori IKEURA, Tomiichi UETAKE1989 Volume 42 Issue 3 Pages 349-359
Published: September 24, 1989
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe purpose of this study is to examine regional variation of source properties of middle earthquakes for the estimation of irregularities of the coupling along plate boundary, which is effective to the prediction of strong ground motions due to large interplate earthquakes. Strong motion records of acceleration and velocity have been observed at 5 stations since 1983 for earthquakes along the southern part of the Japan trench (off Fukushima prefecture). The magnitude Mj of these events ranges from 4.2 to 6.7 in the JMA scale. Classification of source properties, such as high-, medium-, and low-frequency earthquakes, is made by using the residual values for each earthquake from averaged acceleration response spectra S(T) in the period range shorter than 1s. S(T) is expressed as
logS(T)=a(T)MJ-(b(T)X+logX)+Ci(T)
where a(T), b(I), and Ci(T) are regression coefficients. Ci(T) is determined for each station. X is hypocentral distance. Judging from the dominant period of seismograms used for the magnitude determination, the JMA magnitude shows amplitude of surce spectrum at medium period. It is found that the high-frequency earthquakes mainly occur in the northwestern part of the subduction region, while the low-frequency earthquakes in the southeastern part. The stress drop of high-frequency events is about 300bar, which is meaningfully larger than the average stress drop over the fault plane of large events off Fukushima prefecture. In this region, a series of large earthquakes occurred in 1938. We classify 27 events of MJ≥6 from 1926 to 1938 including the events of the 1938 series into high-, medium-, and low-frequency earthquakes, based on the difference between MJ and MI MI is a magnitude scale determined from the data of seismic intensity, which shows amplitude of source spectrum at higher frequency. Regional variation of source properties of the old events is consistent with that of the recent earthquakes. This indicates that the spatial variation of source properties has not changed at least for the recent 50 years and suggests that the high frequency events show the distribution of sustained asperities along the plate boundary.View full abstractDownload PDF (1284K) -
Yosuke TAGUCHI, Yoichiro FUJII1989 Volume 42 Issue 3 Pages 361-363
Published: September 24, 1989
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (255K) -
Naoyuki KATO, Yasuto KUWAHARA, Kiyohiko YAMAMOTO, Tomowo HIRASAWA1989 Volume 42 Issue 3 Pages 365-369
Published: September 24, 1989
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (467K) -
Shozo MATSUMURA1989 Volume 42 Issue 3 Pages 371-390
Published: September 24, 1989
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe style of seismic observation during the last two decades has drastically changed due to the revolutionary advancement of technology, especially noted in the advent of the telemetry system and computer systems. Introducing the telemetry system into seismic observation resulted in a concentration of a large amount of data, which brought the necessity to change and systematize the style of routine-base data processing. Computer-based automatic processing was a long-time hope of researchers in charge of seismic observation, and they tried to develope various kinds of effective techniques and algorithms for the processing of seismic wave signals, including the automatic reading of seismic wave parameters and the automatic hypocenter locations.
Recent progress in computer technology has made it possible for these researcher's hopes to be actualized. Today, most research institutes utilize computer systems operating in realtime data processing, and offer up-to-date products. Subjects for use are not always defined within a category of usual routine-base processing, but they are expanded into a higher level of processing, such as an automatic monitoring of seismic activity, or automatic detection of precursory phenomena.View full abstractDownload PDF (2788K) -
Kazuki KOKETSU, Hiroshi TAKENAKA1989 Volume 42 Issue 3 Pages 391-403
Published: September 24, 1989
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSWe review recent theoretical studies on wave propagation in the near field of seismic sources. These include theories for horizontally layered media as well as those for irregularly layered media. Ray theory and its extensions are easily applied to arbitrarily inhomogeneous media, but they include serious approximations. The finite difference method is also flexible, but requires extensive computation. Except for these methods, we should note that all the methods currently available for irregularly layered media belong to the category of the method of weighted residuals.View full abstractDownload PDF (1801K)
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