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Volume 32 (1980)
- Issue 12 Pages 721-
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Volume 28 (1976)
- Issue 6 Pages 437-
- Issue 5 Pages 333-
- Issue 4 Pages 253-
- Issue 3 Pages 189-
- Issue 2 Pages 65-
- Issue 1 Pages 1-
Volume 28, Issue 2
Displaying 1-11 of 11 articles from this issue
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T. RIKITAKE, M. J. S. JOHNSTON1976 Volume 28 Issue 2 Pages 65-67
Published: 1976
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSDownload PDF (307K) -
Minoru TAZIMA, Hiroo MIZUNO, Minoru TANAKA1976 Volume 28 Issue 2 Pages 69-84
Published: 1976
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSMean isoporic charts of the geomagnetic horizontal component, declination, vertical component and total force in and around Japan are constructed for epoch 1970.0 on the basis of the results of the 1st order magnetic survey carried out by the Geographical Survey Institute and the observations at magnetic observatories.
A number of local anomalous areas, over which the secular change is larger than the normal one as determined from the overall isoporic charts by 2γ/yr or more, are found. Some of the areas seem to be correlated with tectonic activities such as earthquake occurrence and volcanism.
In addition to the anomalies of local character, a rapid change in the pattern of the secular change distribution in Japan is found within the period of 1950' or an early stage of 1960'. In the same period or thereabout, the maximum of the secular change curve of the vertical component occurred successively in Japan, Siberia and Ural as if a regional magnetic anomaly source had traveled in a north-west direction with a speed on the surface of the earth's core of about 200km/yr. The rapid change in the distribution of isoporic lines in Japan within a period of 10 years or less may be caused by such a regional secular change source.View full abstractDownload PDF (1550K) -
M. J. S. JOHNSTON, B. E. SMITH, R. MUELLER1976 Volume 28 Issue 2 Pages 85-97
Published: 1976
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSSimultaneous measurements of the geomagnetic field with differential proton magnetometers (0.25 gamma sensitivity) have been recorded periodically since 1973 at more than 100 pairs of sites, 8 to 12km apart, along active faults in western U. S. A. Along one 80km test section of the San Andreas fault the data from 7 instruments is continuously telemetered to Menlo Park, California. Probable tectonomagnetic effects with amplitudes of about 1 and 1.8 gammas have been observed for earthquakes with magnitudes 4.2 and 5.2 respectively. The corresponding stress changes for simple dislocation models are in the range 10 and 100 bars respectively. Magnetic and electrical response differences and site separation appear to be the most important factors determining discrimination limits for tectonomagnetic signals.View full abstractDownload PDF (2166K) -
Seismo-magnetic Effect in a Possible Association with the Niigata Earthquake in 1964Takesi NAGATA1976 Volume 28 Issue 2 Pages 99-111
Published: 1976
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSThe source mechanism of the Niigata earthquake (M=7.5), which occurred on June 16, 1964, is represented by a thrust fault of about N10°E in strike, about 60° in dip, about 100km in length, about 20km in width and about 4m in displacement discontinuity. The source model can well represent the observed co-quake land deformations along the sea coast on land and on the sea bed in the neighbourhood of the epicenter. The average shear stress along the fault plane is estimated to be 130-150 bars.
The geomagnetic field in the epicentral area was locally deviated by 20γ at maximum during the pre-quake period and the co-quake local geomagnetic variations. The distribution patterns of the pre-quake and co-quake geomagnetic variations are negatively correlated with a correlation coefficient of about -0.7. These variations are proved to be attributable to the tectonomagnetic effects caused by an accumulation and a release respectively of the shear stress within the earth's crust, provided that the average intensity of magnetization of the earth's crust is about 5×10-3emu/cm3.View full abstractDownload PDF (1252K) -
Paul M. DAVIS1976 Volume 28 Issue 2 Pages 113-122
Published: 1976
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSA volcano containing a pressurized magma chamber is approximated by a centre of dilatation embedded in a semi-infinite isotropic elastic medium. Stresses corresponding to a given surface strain are used to compute the associated piezomagnetic surface anomaly field. Comparison with results taken from a proton precession magnetometer array on Kilauea volcano, Hawaii indicates that stresses associated with shallow centres of inflation beneath the volcano are less than those expected from an elastic model. The most plausible explanation appears to be anelastic deformation of the volcano, leading to an effective crustal rigidity an order of magnitude less than that for competent basalt.View full abstractDownload PDF (820K) -
Yilmaz ISPIR, Orhan UYAR, Yalçin GÜNGÖRMÜS, Naci ...1976 Volume 28 Issue 2 Pages 123-135
Published: 1976
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSIn Turkey, studies on the tectonomagnetic effect have started at the end of 1970. Taking simultaneous measurements of the total geomagnetic field at a few stations in NW Turkey by proton precession magnetometers, some tectonomagnetic effects up to 50 nT accompanying felt earthquakes are observed within the period December 1972-March 1975. A linear relation is obtained between the magnitude and distance of the earthquakes which are close to the magnetic stations (less than 75km), and the observed tectonomagnetic effect.
Temporary magnetic measurements along a profile show that the tectonomagnetic effect increases towards the fault.
The last part of this study shows that it will be useful and possible to use the magnetic records of the Istanbul-Kandilli, Panagyurishte and Surlari observatories to compute tectonomagnetic effects of the past.View full abstractDownload PDF (1114K) -
Yilmaz ISPIR, A. Mete ISIKARA, Hüseyin ÖZDEN1976 Volume 28 Issue 2 Pages 137-143
Published: 1976
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSThe secular variation of the geomagnetic field and the variation in the local magnetic constant (G) between the epochs 1965.0 and 1970.0 for whole Turkey are considered. G isolines are found to be almost perpendicular to the stress directions obtained by earthquake mechanism studies for this region. There is also a good correlation between the values of G and the released energy density which is calculated for only the west part of Turkey, and the depth of felt earthquakes.View full abstractDownload PDF (639K) -
Tsuneji RIKITAKE1976 Volume 28 Issue 2 Pages 145-156
Published: 1976
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSElectromagnetic induction in a two-dimensional conductor having a rectangular cross-section embedded in a less conductive half-space is studied. Supposing that such a system of conductors represents an electric model of a dilatant region in the earth's crust, an appreciable enhancement of the horizontal magnetic field is found over the portion of the earth's surface immediately above the higher conductivity region for a certain frequency range of the inducing field.
The possibility of monitoring an underground dilatant region by means of an observation of short-period geomagnetic variations is thus suggested.View full abstractDownload PDF (1072K) -
Kazuo YANAGIHARA, Tetsuro NAGANO1976 Volume 28 Issue 2 Pages 157-163
Published: 1976
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSElectrical conductivity change of the earth interior is confirmed in relation with earthquake occurrences by using transfer functions which connect three components of geomagnetic variation. During 22 months from August 1973 to May 1975, 6 conspicuous changes of transfer functions are found at Kakioka coinciding with 10 large and near earthquakes. High seismic activity extends near the edge of a local conductivity anomaly in the vicinity of Kakioka.View full abstractDownload PDF (618K) -
I. K. REDDY, R. J. PHILLIPS, J. H. WHITCOMB, D. M. COLE, R. A. TAYLOR1976 Volume 28 Issue 2 Pages 165-178
Published: 1976
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSA feasibility study is being made to monitor possible electrical resistivity changes preceding the earthquakes. Numerical calculations, based on dilatancy hypothesis, indicate that the resistivity changes as much as 60 percent can be possible at some of the Southern California sites. Preliminary magnetotelluric measurements in the eight month period indicate that changes in the resistivities greater than 10 percent can be monitored by magnetotelluric measurements. The observed scatter in the magnetotelluric measurements are within the random errors of the estimates, and no major earthquake activity is reported in the vicinity of these sites, during this period.View full abstractDownload PDF (1411K) -
Hitoshi MIZUTANI, Tsuneo ISHIDO1976 Volume 28 Issue 2 Pages 179-188
Published: 1976
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSLocal magnetic field variation observed during the Matsushiro earthquake swarm in central Honshu, Japan, is well correlated with the variation of spring-water outflow but not with that of the seismic activity. This indicates that the origin of the magnetic field variation is not the stress-induced piezomagnetic effect but may be the water-induced electrokinetic effect proposed by MIZUTANI et al. (1975). The electrokinetic effect combined with the observed amount of water discharge is found to give the correct magnitude and sign of the local magnetic field variation observed at the two stations in Matsushiro area.View full abstractDownload PDF (952K)
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