Monitoring of time dependent electrical resistivity by magnetotellurics.

Reddy, I. K.; Phillips, R. J.; Whitcomb, James H.; Cole, David M.; Taylor, Robert A.

doi:10.5636/jgg.28.165

Cited by 28 publications

(12 citation statements)

References 17 publications

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“…The magnetotelluric method has also been used for studies of crustal resistivity changes REDDY et al, 1976;PHILLIPS et al, 1977;KURTZ and NIBLETT, 197$). However, no unambiguous changes have so far been reported in association with earthquake occurrences.…”

Section: An Example Of Time-dependence Of the Electric Fieldmentioning

confidence: 99%

“…As an alternative to the above conventional method, we can rely on the principle of electromagnetic induction in the earth by geomagnetic variations originating outside of the earth (YANAGIHARA, 1972;MIYAKOSHI, 1975;HONKURA et al, 1976;REDDY et al, 1976;PHILLIPS et al, 1977;KURTZ and NIBLETT, 1978;RIKITAKE, 1979;HONKURA and TAIRA, 1983). However, some problems remain unsolved in the electromagnetic induction method; for example, how much amount of change would we expect for respective observational quantities and to what spatial extent would anomalous changes be observable for a localized resistivity anomaly in an earthquake source region and its vicinity?…”

Section: Introductionmentioning

confidence: 99%

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Local anomaly in magnetic and electric field variations due to a crustal resistivity change associated with tectonic activity.

Honkura

Kubo²

1986

J. geomagn. geoelec

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Electromagnetic response is examined for a local three-dimensional resistivity anomaly embedded in the earth's crust of uniform resistivity , in order to interpret time-dependence of horizontal amplitudes as well as transfer functions for shortperiod geomagnetic variations at an observation site in the Izu region, Japan. The results of numerical estimation indicate that the detected enhancement of about ten percent in horizontal amplitude can be well explained by a local decrease, amounting to one order of magnitude, in crustal resistivity, on the condition that the observation site is located over the area of resistivity decrease. In this situation no marked change is expected for transfer functions; this is consistent with the observation . The results of numerical estimation also suggest that electric as well as magnetic field measurements are useful for detecting crustal resistivity changes; for instance , changes are expected in the amplitude of induced electric field, as would be reflected in apparent resistivity changes in magnetotellurics, and also in polarization angle of the electric field. It should be noted, however, that no detectable precursory changes are expected unless observation sites are located close to the area of resistivity change presumably corresponding to an earthquake source area and its vicinity.

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Section: An Example Of Time-dependence Of the Electric Fieldmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Local anomaly in magnetic and electric field variations due to a crustal resistivity change associated with tectonic activity.

Honkura

Kubo²

1986

J. geomagn. geoelec

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“…However, analysis of simultaneous data from Charlevoix and Lac la Batture (70km distant) indicate that power ratios of the magnetic components do not vary by more than 9%. REDDY et al (1976) demonstrate how the amount of downward bias may be estimated from the multiple coherence. Because of the stringent criteria we have used for selection of good data the impedances shown in this paper could not be biased downward by more than 5 to 10% using their assumptions.…”

Section: Data Analysesmentioning

confidence: 99%

“…Any estimates that have power less than a specified minimum are rejected. In addition, any estimates which give a multiple coherency between computed and measured electric fields less than 0.9 are rejected (REDDY et al, 1976). The remaining estimates are averaged into frequency bands from which various parameters are calculated.…”

Section: Data Analysesmentioning

confidence: 99%

Time dependence of magnetotelluric fields in a tectonically active region in eastern Canada.

Kurtz¹,

Niblett²

1978

J. geomagn. geoelec

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Magnetotelluric 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.

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“…Reddy et al (1976) give an account of the influence of bias (measurement-noise) and random errors on the magnetotelluric response functions. Gamble et al (1979) have recently discussed the use of remote reference components (E or H) to obtain an unbiased estimate of the impedance tensor.…”

Section: Data Processing and Error Determinationmentioning

confidence: 99%

The time-dependence of electromagnetic response functions

Beamish¹

1982

Geophysical Surveys

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Abstract. Dynamic processes within the Earth axe capable of modifying many of its physical properties. This review considers the modification of electrical resistivity mainly by time-changes in the stressfield experienced by crustal materials. Laboratory experiments indicate that certain rock types, whose resistivity is controlled by the volume and geometry of microcracks, can undergo large resistivity variations in response to the typical strain accumulation and release that accompanies major earthquakes. Electromagnetic response functions axe reviewed with regard to their ability to monitor timechanges of resistivity in active regions. Some examples of the different experimental techniques used to investigate precursory changes in response functions prior to earthquakes are noted. The problems and successes of the subsequent correlation and interpretation of the derived response as a function of time are then discussed. Only relatively few controlled and integrated studies of time-dependent electromagnetic response functions exist. Those which are available, however, emphasise that changing stress-differentials occurring before major earthquakes can be monitored using suitable electromagnetic techniques.

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Monitoring of time dependent electrical resistivity by magnetotellurics.

Cited by 28 publications

References 17 publications

Local anomaly in magnetic and electric field variations due to a crustal resistivity change associated with tectonic activity.

Local anomaly in magnetic and electric field variations due to a crustal resistivity change associated with tectonic activity.

Time dependence of magnetotelluric fields in a tectonically active region in eastern Canada.

The time-dependence of electromagnetic response functions

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