Journal of Physics of the Earth
Online ISSN : 1884-2305
Print ISSN : 0022-3743
ISSN-L : 0022-3743
Volume 37, Issue 6
Displaying 1-3 of 3 articles from this issue
  • Shigeru NAKAO, Alan T. LINDE, Satoshi MIURA, Masaaki MISHINA, Akio TAK ...
    1989 Volume 37 Issue 6 Pages 357-383
    Published: 1989
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
    The response of strain to atmospheric pressure changes is studied for six borehole strainmeter sites in Tohoku district, Japan. The analysis is carried out by two methods: one is time domain filtering and the other is Fourier transform in frequency domain. Though the responses at Oga (OGA), Nibetsu (NIB), Honjo (HOJ), and Gojome (GJM) are frequency independent, the response at Tazawako (TAZ) clearly depends on frequency. This phenomenon is not expected for an elastic or viscoelastic medium, but is due to the movement of groundwater through the medium. We simulate the frequency dependence using a fluid-filled porous medium model (Bum., 1941). This model explains the frequency-dependent response at TAZ and gives the porosity of 22% and the permeability of 2.5×10-7 cm/s beneath this station.
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  • Ichiro OHNO, Kazuyoshi TAKAICHI, Yasuo ENDO, Ryoji GOTO, Atsuo TAKAHAS ...
    1989 Volume 37 Issue 6 Pages 385-400
    Published: 1989
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
    We carried out a gravity survey by means of LaCoste and Romberg gravity meters in northwestern Shikoku, Japan, and presented a detailed Bouguer anomaly map. The most significant feature of the .map is the anomaly pattern along the Median Tectonic Line (MTL). We regarded it as a pattern due to the sharp density contrast between both sides of the MTL, and analyzed it assuming a simple step model of a uniform horizontal slab with a dipped end. We also measured densities of rocks that are distributed in the surveyed area. Optimum models obtained on three profiles are 2 km in thickness, 22° in dip, and 0.30 g/cm3 in density contrast approximately.
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  • Tooru OOIDA, Fumihito YAMAZAKI, Iwao FUJII, Harumi AOKI
    1989 Volume 37 Issue 6 Pages 401-416
    Published: 1989
    Released on J-STAGE: April 30, 2009
    JOURNAL FREE ACCESS
    The damaging earthquake (M=6.8) on September 14, 1984 was a strike-slip faulting trending ENE-WSW across an area of earthquake swarm near Ontake volcano, central Japan. The rupture was 12 km long, about 10 km wide and very shallow, though there was no break on the surface. The earthquake occurred near the boundary of crustal blocks between two adjacent earthquake swarms that have been markedly active since 1976. The expansion of aftershock activity to the west and to the east was obvious, though the rupture pattern was complicated. The largest aftershock of M=6.2 to the west of the main shock was conjugated with the main fault. The largest to the east was a reverse faulting. However the pressure axes of these faultings were the same as that of the main shock. The difference between these fault types might be controlled by block boundaries with different directions around the volcano.
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