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Volume 32 (1980)
- Issue 12 Pages 721-
- Issue 11 Pages 671-
- Issue 10 Pages 585-
- Issue 9 Pages 507-
- Issue 8 Pages 431-
- Issue 7 Pages 365-
- Issue 6 Pages 309-
- Issue 5 Pages 265-
- Issue 4 Pages 181-
- Issue 3 Pages 129-
- Issue 2 Pages 67-
- Issue 1 Pages 1-
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Volume 30 (1978)
- Issue 6 Pages 619-
- Issue 5 Pages 477-
- Issue 4 Pages 299-
- Issue 3 Pages 131-
- Issue 2 Pages 65-
- Issue 1 Pages 1-
Volume 30, Issue 5
Displaying 1-16 of 16 articles from this issue
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M. Fuller, M. Johnston, T. Yukutake1978 Volume 30 Issue 5 Pages 477
Published: 1978
Released on J-STAGE: August 11, 2011
JOURNAL FREE ACCESSDownload PDF (57K) -
V. A. SHAPIRO, M. J. S. JOHNSTON1978 Volume 30 Issue 5 Pages 479-480
Published: 1978
Released on J-STAGE: March 12, 2010
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Yu. P. SKOVORODKIN, L. S. BEZUGLAYA, T. V. GUSEVA1978 Volume 30 Issue 5 Pages 481-486
Published: 1978
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSHigh-precision simultaneous observations of the geomagnetic field have been made over areas with fault displacements and junctions of mountain structures in Tajikistan using proton magnetometers MPP-1 with 0.1γ sensitivity. The optimal duration and frequency of resurveying as well as the detection level of possible tectonomagnetic variations (0.6γ) have been experimentally determined.
Examples of characteristic local geomagnetic variations possibly associated with changes of tectonic stresses are given. Oscillations with periods of one or a few weeks and amplitudes of 0.7-1.5γ occur during seismically quiet times, and monotonic variations continuing over a month with subsequent change of sign and a tendency for rapid recovery to the former level occur shortly before energy class K>11 earthquakes (on the Rautian scale, where K=1.8ML+4).View full abstractDownload PDF (624K) -
V. A. SHAPIRO, K. N. ABDULLABEKOV1978 Volume 30 Issue 5 Pages 487-492
Published: 1978
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSPortable proton magnetometers with a sensitivity of 0.1nT operated before, during and after the moment of the magnitude M=7.3, 17th May 1976, Gazly earthquake. Magnetometers were operating essentially at the epicenter at the Kara-Kyr station and 170km to the northeast at the Tamdybulak. Measurements were made during the period 13-22 May 1976. No variations of the geomagnetic field total force with an amplitude exceeding 0.1nT were seen during the earthquake. Similar results were obtained from the magnetic measurements during 12 aftershocks with M≥4.5 which followed the main quake. The profiles of the changes of the geomagnetic field during these 12 aftershocks were stacked. The stacked plot shows no variations with amplitude greater than 0.1nT.View full abstractDownload PDF (542K) -
V. A. SHAPIRO, A. L. ALEINIKOV, A. A. NULMAN, V. A. PYANKOV, A. V. ZUB ...1978 Volume 30 Issue 5 Pages 493-502
Published: 1978
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSSecular variation anomalies (SVA) of two types were revealed as a result of high-precision measurements of the geomagnetic field in the Urals. The results suggest significantly non-uniform tectonic stresses in the Urals. An attempt to measure the time dependence of stress variations was made. An anomaly of the first type is characterized by the steady growth of the field at a rate of 2-3nT/year. Laboratory experiments with the rocks showed that similar changes might be caused by the changes of magnetic susceptibility and remanent magnetization with changes of hydrostatic pressure of about 10bars. The anomalies of second type border the zone of folded Urals to the East and the West. They exhibit sign changes in trends of up to ±20nT/year. These anomalies are probably caused by the change of the rock conductivity because of changes in pore pressure in the zones of thrusting.View full abstractDownload PDF (1022K) -
V. A. SHAPIRO, A. N. PUSHKOV, K. N. ABDULLABEKOV, E. B. BERDALIEV, M. ...1978 Volume 30 Issue 5 Pages 503-509
Published: 1978
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSInvestigations of local geomagnetic field changes have been carried out in Middle Asia in the following regions: Tashkent, including Charvak reservoir, Fergana and Kyzyl-Kum. Since 1968, a variety of total field features have been observed there, including: (a) slow changes at separate stations, which may be explainable by compression or tension of individual earth's crustal blocks; (b) a variety of field changes with amplitudes of a few gammas and periods of 0.5-2 years; (c) variations, which may be due to different conductivity of rocks; (d) anomalous changes in the fracture zones; (e) anomalous variations in the Charvak region, connected with reservoir filling. The amplitudes of these variations are 3-5nT/year at Fergana, 8-9nT/year at Kyzyl-Kum, 20-25nT/year at Tashkent regions and up to 15-25nT/year at Charvak reservoir area. Sometimes these anomalous changes are correlated with seismic activity (for example, Tashkent 1968 earthquakes).View full abstractDownload PDF (652K) -
M. J. S. JOHNSTON1978 Volume 30 Issue 5 Pages 511-522
Published: 1978
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSData from an array of proton magnetometers in central California indicate that a systematic decrease in magnetic field of about 2γ in 5 years has occurred in a localized region near Anzar, California, just north of the creeping section of the San Andreas fault. This field change has most likely resulted from changes in crustal stress in this region, although an unknown second-order effect of secular variation cannot be excluded as a alternate explanation. Tectonomagnetic models have been developed using dislocation modeling of slip on a finite section of fault. Assuming a fault geometry and rock magnetization, these models relate changes in stress, fault slip, and fault geometry to surface magnetic field anomalies. A large-scale anomaly, opposite in sense to that observed but of similar amplitude, would be expected to have accumulated in this area during the past 70 years. A localized 5-bar decrease in shear strain on the fault resulting from about 2cm of slip on a 0.25-km square patch at a depth of 1km beneath the surface trace of the fault opposite the magnetometer could explain the observed data and still be compatible with the geodetic strain measurements in the area. Other models of limited local slip are equally possible. The occurrence of a moderate magnitude earthquake in this region will allow comparison of stress changes estimated by different techniques.View full abstractDownload PDF (1101K) -
Wolfgang MUNDT1978 Volume 30 Issue 5 Pages 523-531
Published: 1978
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSFor about 25 years, measurements of the magnetic components have been carried out at repeat stations in the territory of the GDR. All measurements at common stations of the magnetic surveys for the epochs 1901, 1935, and 1957 were compared. The results of the investigation indicate secular variation anomalies with amplitudes of about 3-4nT/year. These anomalies are obviously partly located in regions with marked recent vertical and horizontal movements. Moreover they seem to be characterized by positive anomalies of the heat flow.View full abstractDownload PDF (681K) -
R. H. WARE, P. L. BENDER1978 Volume 30 Issue 5 Pages 533-537
Published: 1978
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSMeasurements of the difference in total field ΔF(t) have been made over a 16km N-S path near Boulder. The behavior observed is quite different from that for an E-W path. The present accuracy of the narrow line rubidium magnetometers used is about 0.01γ. The N-S variations appear to correlate mainly with variations in H rather than D, and may be associated with either gradients of external fields or currents in shallow conductivity anomalies. More recently three magnetometers have been set up on a straight E-W line so that the ‘second difference’ can be measured, and a transfer function from field component variation to the second difference can be determined. A generalization of this approach will be used for analyzing USGS tectonomagnetic data from California.View full abstractDownload PDF (459K) -
B. E. SMITH, M. J. S. JOHNSTON, R. O. BURFORD1978 Volume 30 Issue 5 Pages 539-548
Published: 1978
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSComparison between local variations in magnetic field, long-term changes in creep rate, and local earthquakes have been made for the seismically active and creeping section of the San Andreas fault between the most southern extent of the 1906 earthquake fault break and the most northern extent of the 1857 break, for the period early 1974 through mid-1977. The data utilized are from stations located near the two ends of this section of the San Andreas fault where strain accumulation is expected. The proton precession magnetometer stations included in this study have recorded local magnetic field variations up to 1.8γ with durations of a few minutes to several months. The creep data indicated changes in creep rate of up to 10mm/year lasting for 6 months or more and a close similarity between the changes in creep rate on two adjacent creepmeters about 7km apart. Earthquakes with magnitudes less than 4.0 do not appear to correspond in time to local changes in magnetic field greater than 0.75γ or variations in the creep rate. There is no general correspondence between creep events and magnetic field variations. There is, however, an approximate correspondence, in both space and time, between the long-term changes in creep rate and the variations in magnetic field. In order to explain the observations presented in this study, it appears necessary to allow for a substantial amount of deep aseismic slip without any obvious attendant changes in the time distribution or size of the local earthquakes.View full abstractDownload PDF (1114K) -
Junichiro MIYAKOSHI, Akira SUZUKI1978 Volume 30 Issue 5 Pages 549-560
Published: 1978
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSGeomagnetic and telluric current observations were conducted on and around the seismically active fault, Yoshioka-Shikano Fault, from 1976 to 1977.
The confined plane of the geomagnetic variation expressed as ΔZ=AΔX+BΔY, was calculated for each station by applying the transfer-function techniques or the least-square method to the records of Pi 1-2 type pulsations.
It was found that the landward increasing tendency of the A values of the confined planes caused by the electromagnetic coastal effect of the Sea of Japan, was slightly interrupted on the northern edge of the fault and also, that the amplitude of the N-S component of geomagnetic variation (ΔX) was considerably enhanced upon the fault. These results are proposed to be due to the effect of the swelling of the electrically conducting medium in the crust beneath the seismically active fault.
A tentative analysis was also made for the telluric current records observed on the fault, comparing it with the data obtained at the same site just after the Tottori Earthquake. As for the direction of polarization of the electric field there was no noticeable difference between them.View full abstractDownload PDF (918K) -
R. D. KURTZ, E. R. NIBLETT1978 Volume 30 Issue 5 Pages 561-577
Published: 1978
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSMagnetotelluric fields have been monitored for 3 years near the centre of seismicity in a tectonically active region on the north shore of the St. Lawrence River. The results indicate that electrical properties of upper crustal layers are strongly time-dependent in this area, and changes of more than 30% in the impedance tensor have been detected over a period of a few months. However, the most important part of the measured time dependence appears to be a trend increase in impedance of about 14% per year. There have been only two earthquakes greater than magnitude 3.0 in the area since recording began in 1974 and it has not been possible to develop a clear association between seismic activity and resistivity changes. Seasonal variations in the temperature and salinity of the nearby St. Lawrence River may be a contributing factor. Much less change in impedance was observed at similar MT recording stations located outside the zone of seismicity.View full abstractDownload PDF (1797K) -
R. S. CARMICHAEL1978 Volume 30 Issue 5 Pages 579-584
Published: 1978
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSPiezomagnetic field variations can result from tectonic stress changes in the focal zone of an impending earthquake. Interpretation of such observed tectonomagnetic effects requires modeling of the stress response of magnetic properties of the lithosphere. Calculations have been made to estimate the here piezomagnetic effect as a function of depth, by considering the effect of stress on the magnetization of magnetite (Fe3O4) with increasing temperature and hydrostatic pressure. The responsiveness of magnetization to seismotectonic stress is gauged by an appropriate balancing of magnetocrystalline and magnetoelastic anisotropy energies. The calculations indicate that magnetite becomes progressively more responsive to stress at depth increases. The rate of change depends on the local geothermal gradient. The upper 15km of the lithosphere is likely to be the most important in yielding observable piezomagnetic field effects. Such shallow-focus earthquakes are expected to be best for monitoring tectonomagnetic anomalies for earthquake prediction.View full abstractDownload PDF (511K) -
A. A. NULMAN, V. A. SHAPIRO, S. I. MAKSIMOVSKIKH, N. A. IVANOV, Joon K ...1978 Volume 30 Issue 5 Pages 585-592
Published: 1978
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSThe erects of hydrostatic pressure up to 2.7kb on the susceptibility of magnetite single crystals, rocks and ore, and synthetic samples were studied. Susceptibility was measured using both static and alternating-frequency methods, with cyclic change of hydrostatic pressure and with time-dependent experiments. For a single crystal, susceptibility at saturation remanence decreases with pressurization, by about 25% for 2.5kb, and is recovered reversibly upon release of pressure. For rocks and ore, susceptibility k0 at small natural remanence increases slightly up to 0.2-0.8kb, then decreases at higher pressures at rates up to -10%/kb. It recovers upon pressure release. For cyclic pressurization without a time lag between cycles, the initial increase is not observed. Annealing increases the value of k0, and also suppresses the initial increase of k0 with pressure. Time lags of hours between pressure cycles result in recovery of pre-pressurization values of susceptibility. This work is intended to assist in the interpretation of stress-induced changes observed for rocks in the earth's lithosphere. Applications are in understanding piezomagnetic field changes as precursors for earthquake prediction, and study of other secular tectonomagnetic changes.View full abstractDownload PDF (820K) -
Jacques REVOL, Ron DAY, Michael FULLER1978 Volume 30 Issue 5 Pages 593-605
Published: 1978
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSPolycrystalline magnetite and rock samples have been subjected to uniaxial compression and stress cycling at room temperature. The changes in the components of remanent magnetization were recorded continuously as a function of stress, and the changes in direction and total intensity of magnetization were inferred. Different types of response were recognized, according to the type of magnetization the sample was carrying, i. e., high field or weak field remanence. The anomalous increase of weak field remanence previously reported, appears partly reversible under stress cycling. However, the changes in the lowest stress range are irreversible and reduce the zero stress magnetization from cycle to cycle. Reversible rotations of the magnetization vector of as much as 180° were observed during each half cycle and were primarily due to changes in the sign of the component of magnetization parallel to compression. An andesite whose magnetic phases are single domain according to hysteresis criteria showed a much smaller effect regardless of the type of magnetization it carried. These results again draw attention to the variety of stress responses and the importance of three component observations in field attempts to detect seismomagnetic precursors.View full abstractDownload PDF (1217K) -
T. L. HENYEY, S. J. PIKE, D. F. PALMER1978 Volume 30 Issue 5 Pages 607-617
Published: 1978
Released on J-STAGE: March 12, 2010
JOURNAL FREE ACCESSPreliminary stress sensitivities of NRM of two rocks from along the San Andreas fault, California, have been investigated using a cryogenic magnetometer and uniaxial pressure vessel. Of particular interest has been the irreversible behavior in response to cycling in the stress range 0-500bars. The effect of hydrostatic pressure has also been examined. Sensitivities parallel to the compression axis behave as predicted by simple theory and show irreversible behavior during initial stress cycles. In contrast, transverse sensitivities show significant deviations from simple theory. Stress sensitivities of NRM do not appear to be appreciably affected by increase in hydrostatic pressure up to 0.5kb.View full abstractDownload PDF (1066K)
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