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Volume 45, Issue 2
Displaying 1-14 of 14 articles from this issue
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Yasunori TSUBOI, Tamao SATO1992 Volume 45 Issue 2 Pages 121-128
Published: September 30, 1992
Released on J-STAGE: July 01, 2010
JOURNAL FREE ACCESSWe have studied the number of aftershocks with JMA magnitude (MJ)≥5 occurring within the next 30 days after large shallow earthquakes (MJ≥6.9) in Japan. As a whole, the relationship between the number of aftershocks (N), and the moment magnitude (MW) of the main shock is similar to that obtained by SINGH and SUÁREZ (1988) for the events along the entire circum-Pacific subduction zones. For the same MW, N is generally smaller for the interplate earthquakes along the Nankai trough, where the Philippine Sea plate subducts, than for the interplate earthquakes along the Kurile and Japan trenches where the Pacific plate subducts. This relative lack and excess of N correlates with the supposedly strong and weak coupling of the two plate boundaries, respectively. On the other hand, N for the intraplate earthquakes on the Japan Sea side is similar to that for the interplate earthquakes along the Kurile and Japan trenches. Thus, it is difficult to explain the relative lack and excess of N in different tectonic settings in terms of interplate and intraplate events.
It is reasonable to expect that N should correlate with the source spectrum of a main shock since they can both be affected by the degree of heterogeneity on and around the fault plane. We examined the correlation between N and the source type of a main shock that is determined by comparing the size of felt area with MJ. The source type is regarded as reflecting the enrichment of the source spectral amplitude at higher frequencies (1-5Hz) relative to that at lower frequencies (around 0.3Hz). Contrary to expectation, no clear correlation was found between them. It is concluded that the relationship between the aftershock activity and the source spectrum of a main shock is so complicated that it cannot simply be characterized in terms of such parameters as the number of aftershocks and the source type adopted in this study.View full abstractDownload PDF (918K) -
Yoshio MURAI, Yoshimasa KOBAYASHI1992 Volume 45 Issue 2 Pages 129-143
Published: September 30, 1992
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe scattering and attenuation properties of S-coda waves are investigated by analyzing seismic waves recorded during the off Ito earthquake swarm in 1989. First, on the basis of the analysis of tripartite array data, it is shown that coda waves of 3 earthquakes are propagated from all directions and their apparent velocities are estimated. Next, the values of Q-1 of coda waves, QC-1, are estimated in six frequency bands from 1.0 to 32.0Hz for two lapse time windows by using the single backscattering model. By fitting QC-1 from the long lapse time window to the power law frequency dependence, QC-1∝fn, the power n is estimated as -0.81 for the band covering 1.0 to 16.0Hz. The values of QC-1 for the two lapse time windows are compared in four frequency bands from 2.0 to 16.0Hz. While a good agreement is obtained in the 2.0Hz band, discrepancy is large in the 16.0Hz band. In addition, apparent velocities of coda waves are obtained within ±0.5km/s of the phase velocities of Rayleigh waves predicted for the subsurface structure over the frequency range from 2.0 to 4.0Hz. These results suggest that coda waves at around 2.0Hz contain backscattering surface waves and that the values of QC-1 reflect the attenuation properties in the shallow crust exclusively. On the other hand, for frequencies higher than 4.0Hz a decrease of the values of QC-1 with lapse time may be attributed to a decrease of Q-1 with depth. We compare QC-1 for earthquakes recorded before and after the two major events in the swarm, the July 9 Ito-Oki earthquake (M5.5) and the July 13 volcanic eruption. No appreciable temporal change of QC-1 is found associated with these events. The heterogeneity size or the maximum crack length is estimated to be longer than 0.6km from the frequency at which QC-1 takes the peak value.View full abstractDownload PDF (1675K) -
GSJ 90-1 Hidaka, HokkaidoTakanobu YOKOKURA, Teruki MIYAZAKI, Yasushi WATANABE, Tetsuro URABE1992 Volume 45 Issue 2 Pages 145-156
Published: September 30, 1992
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSThe seismic profiling experiment using vibrator sources was conducted at Hidaka, Hokkaido, to clarify the deep geological structure in this area and to estimate an applicability and field parameters of the seismic survey in geologically complex area and in noisy circumstances. The preliminary results show that the diversity stacking suppresses burst noises like trafic ones and that the band-limited deconvolution filter seems to eliminate high frequency noise. Although the obtained seismic data are so noisy, a careful velocity analysis discriminates weak coherent signals and, therefore, provides a velocity structure in this area. The velocity structure is shown to be in harmony with the gravity data and surface geology in this area.View full abstractDownload PDF (1708K) -
Part 2: Evaluation of Liquefaction Potential in Kohoku Area, Muroran City, Hokkaido, JapanSadaiku HATTORI, Noritoshi GOTO, Kenhiro KOSEKI, Tadashi TAKAYA, Takeh ...1992 Volume 45 Issue 2 Pages 157-167
Published: September 30, 1992
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSIn the present paper, liquefaction potential and liquefaction risk were evaluated for an experimental site in Muroran city by using critical S wave velocity. What is called FL-method for evaluation of liquefaction potential uses N-values by penetrating test in boreholes. The present method, on the other hand, compares S wave velocity of the ground with the critical S wave velocities which correspond to such N-values as the safety ratios in FL-method come to 1.0. As S wave velocity can be easily measured by the surface wave method, in which S wave velocity is estimated by making use of Rayleigh wave generated from a vibrator, it is favorable to use the critical S wave velocity from practical points of view. The experimental site is in the ground of branchoffice of Muroran-city fire service, which was one part of the campus of Khohoku Junior High School at the time of the 1968 Tokachi-Oki earthquake. The site is located at the northern coastal area of Muroran bay and the ground was damaged by the 1968 Tokachi-Oki earthquake. The ground model and the critical S wave velocity of the site area were estimated on the basis of geological section of a borehole, and S wave velocities for seven points were measured by the surface wave method. The evaluation of liquefaction potential and liquefaction risk were made for the above seven points. The results show that for almost all of points, liquefaction will occur for both maximum accelerations of 160cm/s2 and 200cm/s2 on the ground surface. But levels of liquefaction risk are low for the former and very high or high for the latter. It is said, therefore, that the experimental site may be damaged again by an earthquake similar to the 1968 Tokachi-Oki earthquake. The permanent displacements due to liquefaction were estimated to be 1.6m and 2.4m for the above two maximum accelerations. The results of evaluation of liquefaction potential for seven points, which were carried out by the present method and the FL-method are compatible each other. We can say that the present method is useful for the microzoning on liquefaction potential in urban area where the zoning must be done in very details.View full abstractDownload PDF (3590K) -
Tokutaro HATORI1992 Volume 45 Issue 2 Pages 169-176
Published: September 30, 1992
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSAdding to the Russian data, the behaviors of the 1952 Kamchatka, 1960 Chile and the 1968 Tokachi-Oki tsunamis propagated into the Japan Sea from the Tsugaru Straits are investigated. Wave-heights of the 1960 Chile tsunami reached 1.0-1.5m at the West Hokkaido and Tsugaru coasts. The ratio of amplitude of these coasts to that of Hakodate was 0.2-0.4. For the 1952 Kamchatka tsunami, the ratio at Nakhodka was 0.3. While, wave-heights at the West Hokkaido to Tsugaru coasts for the 1968 Tokachi-Oki tsunami being the short period decreased one-tenth high at Hakodate. Wave-heights observed with the wave-periods of 70min and 50min for the Chile and Kamchatka tsunamis are largest, respectively. The maximum wave of the Kamchatka and Chile tsunamis occurred 12 hours or more late after the initial wave, and the undulation continued for two days. According to the refraction diagram, the wave-rays concentrate at the Primorskiy and Korean coasts, but most of the energy trapped on the shelf of Japanese coast. For the long-period tsunamis, it is indispensable to take precautions against the effet of currents.View full abstractDownload PDF (594K) -
Masajiro IMOTO1992 Volume 45 Issue 2 Pages 177-185
Published: September 30, 1992
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSChanges in the rate of microearthquake activity before five earthquakes with magnitude 6 and larger are studied for data from the Kanto area in central Japan. Earthquake occurrences are assumed to follow the Poisson proccess of which the parameter (Poisson rate) may change at most once in the studied period. The period for study is assumed to be divided into two periods, a period of background seismicity and the succeeding anomalous period. Using Akaike Information Criterion, a significant change in the rate can be detected. For each earthquake, several sequences are analysed with different magnitude bands and different spherical source volumes. Increases in the rate are more frequently detected than decreases. Increases in the rate from a simulation are less frequent than those of the actual cases. Using a proper criterion, a probability gain for earthquake prediction based on rate increase is estimated to be about 6. Magnitude shifts, which might cause man-made changes in the rate, are discussed based on differences between the catalog magnitude and station magnitudes. In most cases, magnitude shifts appear little and could not explain for such large changes as those detected. As for depth distributions, differences in mean depth between the two periods are found for a few sequences.View full abstractDownload PDF (940K) -
Development of Experimental ApparatusTohru WATANABE, Mineo KUMAZAWA, Kei KURITA, Tadashi MASUDA1992 Volume 45 Issue 2 Pages 187-198
Published: September 30, 1992
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSA new experimental approach for the investigation of macroscopic behavior of partially molten material with relatively small melt fraction is proposed to complement the theoretical approach. The experiment is designed to clarify the interaction between the macroscopic deformation and the textural evolution in partial melts. The three key points of our approach are (1) the use of a binary eutectic system that can be dealt near room temperature, it should have appropriate solid-solid and solid-liquid interfacial energies; (2) the use of concentric-cylinder type rotational deformation apparatus that enables us to perform large strain deformation with a constant sample geometry and in-situ observation of sample structure by the acoustic waves; and (3) the use of a specially designed torque sensor which enables us to perform the precise measurement and the accurate feedback control of stress and/or strain. The ice-brine (KCl-H2O) mixture is used as a practical example for (1). The developed apparatus with (2) and (3) is described in detail, and the technical subjects are analyzed and discussed.View full abstractDownload PDF (5140K) -
Yuki YUSA, Keiji TAKEMURA, Koichi KITAOKA, Kokichi KAMIYAMA, Shoji HOR ...1992 Volume 45 Issue 2 Pages 199-212
Published: September 30, 1992
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSMultichannel seismic reflection profilings and gravity measurements give new information on the subsurface structure and the tectonic movement in the Beppu Bay area located at the northeast end of the Beppu-Shimabara Graben. Beppu Bay is structurally divided into the eastern and the western areas by a distinct tectonic line. In the eastern area, a graben structure whose axis runs parallel to the Median Tectonic Line is revealed by both the reflection profiles and the Bouguer gravity anomalies. The southern and the northern slopes of the graben are composed of the Sanbagawa Belt basement (SB) and the Ryoke Belt basement (RB), respectively. The surface of SB dips 30 degrees to the north at shallow depths and lowers at greater depths, and then SB lies below RB. The analysis of the seismic reflection and the gravity data suggests a possibility that an unknown formation having the similar density as SB may exist between SB and RB in the north part of this area. Many faults and folding structure in the thick sedimentary sequences overlying RB indicate that RB has been moved relatively to SB by dextral strike-slip movement, and has also slipped down along the surface of SB. On the other hand, the western area is subdivided into the main and the north parts. The main part is characterized by a basin structure buried by thick sediments, where an extremely low Bouguer gravity anomaly is observed. Active listric faulting is developed in the north part; the decolloment surface exists at about 300m depth below the sea floor.View full abstractDownload PDF (2990K) -
An application to olivineIsao SUZUKI, Yasushi INOUE, Jun-ichi HIRAO, Hitoshi ODA, Toshiaki SAIT ...1992 Volume 45 Issue 2 Pages 213-228
Published: September 30, 1992
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSComputation of free oscillatory eigenfrequencies and modes is possible for elastically anisotropic spheres. The resonant sphere technique (RST) is now applicable to measurements of elastic and anelastic properties of small specimens with general crystal symmetry. Changes of the eigenfrequencies due to ellipticity are also computable, and this may extend applicability of the method to measurements under pressure and/or temperature. Results for a very small olivine sphere are shown as examples. Simple relationships between elastic constants and density are observed in the forsterite-fayalite binary system. Anisotropic dissipation factors appear to have linear relationships against squared velocities.View full abstractDownload PDF (1565K) -
Toshiki KAKUTA, Hiroki MIYAMACHI, Hiroshi KUBOTA, Akio TAKAGI1992 Volume 45 Issue 2 Pages 229-237
Published: September 30, 1992
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSA notable WNW-ESE alignment of crustal earthquakes, which have been active since the latter half of 1989, was observed along a narrow zone from Amakusa-nada through Izumi City to Kakuto area; it nearly corresponds to a discontinuity presumed in the subducting plate. Focal mechanisms of some events suggested left lateral movements with T-axes of north or northwest trends. Though not comparable in length with the above, alignments of similar trends are also inferred in Central Kyushu, where seismic activities are mainly characterized by NE-SW tectonic lines such as Beppu-Shimabara and Amakusa-nada grabens and Futagawa-Hinagu active fault system.
In a rather small area west off Satsuma peninsula, South Kyushu, crustal earthquakes also swarmed. The seismic zone was composed of two narrow planes steeply dipping and intersecting with each other. The events along the WNW-ESE alignment mentioned above also swarmed especially at the places where the alignment crosses Amakusa-nada graben, NE-SW fault systems in the northwest of Kagoshima prefecture and a graben-like structure trending NE-SW at Kakuto area. Generally speaking, high seismic activity is observed in an area where tectonic lines or alignments of different trends intersect.
Sporadic shallow earthquakes were noticed along “Nobeoka” tectonic line geologically inactive.View full abstractDownload PDF (1233K) -
Shinji KAWASAKI, Yoshimasa KOBAYASHI, Tomoki TSUTSUI1992 Volume 45 Issue 2 Pages 239-245
Published: September 30, 1992
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSSeismic reflection survey was conducted in Fushimi-Momoyama, Kyoto in November 1990. A linear array was spread across the extension of the Momoyama fault, which strikes from north to south at the eastern edge of the Kyoto basin. The length of the survey line was 1200m. A main aim of this survey was to investigate subsurface structure up to the depth of about 1km which possibly reveals the activity of the growth history of the Momoyama hill as well as the Momoyama fault. Seismic reflection survey is capable of imaging sedimentary layers because of its relatively short wavelength. A hydraulic weight dropping machine named “Yuatsu impactor” was used as a source apparatus. Through the data-processing by the CDP method and reverse time migration, the following results mainly were obtained.
(1) The basement and some sedimentary layers were identified. They are bent beneath the surveyline and their maximum dip is about 20 degrees to the west. The depth of the basement is about 300m beneath the Momoyama hill (east side) and about 600m in the Kyoto basin (west side).
(2) From the change of the dip in each layer, we found that the movement forming the Momoyama hill began less than 0.9 million years ago. Additionally, from the depth difference of each layer, the relative velocity of faulting since then is estimated at about 0.2m per 1 thousand years. This indicates that the activity of this movement is B class as noted in “Active Faults in Japan” (1991).View full abstractDownload PDF (961K) -
Hiroyuki TAKAYAMA, Akio YOSHIDA1992 Volume 45 Issue 2 Pages 247-254
Published: September 30, 1992
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSCorrelation of seismic activities in the Kanto, Tokai, and Kinki regions has been investigated. We used an earthquake data file obtained from the JMA Earthquake Catalogue by removing swarm-like earthquakes. We divided the whole region (N33°-36°, E134°-141°, 0-60km) into 6×14×2 blocks and calculated correlation coefficients of the increase rates of seismic activities for every pair of the blocks. Significant positive correlation was found between the shallow seismicity (0-30km) in Wakayama and the deep seismicity (31-60km) in northern Chiba, and between the deep seismicities (31-60km) in southwestern Kii and Choshi.View full abstractDownload PDF (939K) -
Shigeki HORIUCHI, Noriko TSUMURA, Akira HASEGAWA, Syuichiro HORI, Koui ...1992 Volume 45 Issue 2 Pages 255-258
Published: September 30, 1992
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (581K) -
Osamu OKITSU, Yutaka HIRATA, Toshi ASADA, Hideo TSUNAKAWA, Shinichi KI ...1992 Volume 45 Issue 2 Pages 259-261
Published: September 30, 1992
Released on J-STAGE: March 11, 2010
JOURNAL FREE ACCESSDownload PDF (313K)
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