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Volume 33 (1985)
- Issue 6 Pages 485-
- Issue 5 Pages 391-
- Issue 4 Pages 279-
- Issue 3 Pages 157-
- Issue 2 Pages 59-
- Issue 1 Pages 1-
Volume 33, Issue 2
Displaying 1-6 of 6 articles from this issue
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Masanori HORIKE1985 Volume 33 Issue 2 Pages 59-96
Published: 1985
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSEngineering seismology now requires a convenient and easy survey method for S-wave-velocity structures which enables exploration down to the basement even in urbanized areas. We have attempted an application of long-period (0.5Hz to 3.0Hz) microtremors to answer this demand. The method consists of three steps: (1) microtremors are observed using an array of seismometers; (2) their phase velocities are determined by the frequency-wavenumber-spectral analysis of array data; and (3) the S-wave-velocity structure is determined from the obtained phase velocities by the generalized inversion method. As an exploration method, this procedure has several advantages: (1) microtremors can be observed at any time and location; (2) observation is much easier than with other exploration methods; (3) it causes no environmental problems; and (4) geological conditions down to a depth of more than 100m can be inverted, as far as microtremors of required frequency range are observed. The method was applied at two sites located in and near urban areas, and the whole S-velocity structure above the basement was determined. This method proves to be a useful and practical tool for determining S-wave-velocity structures especially in urbanized areas.View full abstractDownload PDF (3185K) -
Toshiki KAKUTA1985 Volume 33 Issue 2 Pages 97-119
Published: 1985
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSWe present a method suitable for ray tracing in a three-dimensional structure composed of several zones. This is a method extended from two-dimensional ray tracing and is characterized by a small number of calculation steps for a ray. Applying this method to four events occurring around Hokkaido and off the east coast of Kyushu, we investigate the anomalous structure in the upper mantle beneath Japan. P velocities of 8.05 and 7.50km/s are estimated as a model in the uppermost parts of the high and low velocity zones, respectively; the velocity difference of 6.8 percent is comparable with those in the studies made to date. At the lower boundary of the high velocity lithosphere, the velocity contrast is suggested to be lower than 2 percent, while it is over 2 to 3 percent at the upper boundary.View full abstractDownload PDF (1931K) -
Kazuki KOHKETSU1985 Volume 33 Issue 2 Pages 121-131
Published: 1985
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSThe reflectivity method of seismogram synthesis is extended to compute near-field seismograms due to a propagating fault. The complete representation of a point dislocation wave-field is made using Fuchs matrices and SH propagator matrices. The inversion of Fourier-Bessel transforms and fault surface integration are carried out numerically with the complex frequency technique and some time-reducing devices. Numerical examples which demonstrate the validity of our extension are also made. One of them shows that body waves are amplified by the sediment layers inferred from refraction experiments compared to those predicted using homogeneous crustal models. This amplification suggests that the effects of sediment layers should be included in the interpretations of near-field seismograms.View full abstractDownload PDF (921K) -
Taku URABE, Kiyoshi SUYEHIRO, Takaya IWASAKI, Naoshi HIRATA, Toshihiko ...1985 Volume 33 Issue 2 Pages 133-147
Published: 1985
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSFive ocean bottom seismographs (OBSs) were dispatched to the source region of the 1983 Japan Sea earthquake (occurred on May 26; M=7.7) by a helicopter only three days after the mainshock. The source region was 40 to 100km off the western coast of northern Honshu. The major part of the aftershock area was covered by the OBS network, which recorded ground motion on magnetic tape continuously for 12 days. Among the vast number of aftershocks recorded, 500 events were selected for reproduction. A precise aftershock distribution was obtained from these data. The aftershock area, which ran along the eastern margin of the Japan Basin, was 140km long in north-south with a width of 40km. The focal depths of the aftershocks were concentrated in a range of 8 to 21km. Since the lithosphere of this region is estimated to be no less than 30km thick, the fracture did not span the entire lithosphere. The geometry of the main fault was suggested by a plane arrangement of the aftershock distribution, which is 30km long in north-south and dips eastward by 15 to 25°. This observation is consistent with the mechanism solution of the mainshock obtained from land data. Not a few hypocenters which do not belong to the eastward-dipping plane may suggest the existence of another major fault plane.View full abstractDownload PDF (1463K) -
Andrzej KIJKO1985 Volume 33 Issue 2 Pages 149-154
Published: 1985
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSDownload PDF (485K) -
So Gu KIM1985 Volume 33 Issue 2 Pages 155-156
Published: 1985
Released on J-STAGE: April 30, 2009
JOURNAL FREE ACCESSDownload PDF (178K)
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