Time Dependence of Magnetotelluric Fields in a Tectonically Active Region in Eastern Canada
Part of the
Advances in Earth and Planetary Sciences
book series (AEPS, volume 5)
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.
KeywordsApparent Resistivity Impedance Tensor Vertical Crustal Movement Measured Time Dependence Apparent Resistivity Curve
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.
, Variations of electric resistivity of mountain rocks connected with tectonic causes, Tectonophysics
, 273–277, 1972.CrossRefGoogle Scholar
and A.S. Orange
, Electrical resistivity changes in saturated rock under stress, Science
, 1525–1526, 1966.CrossRefGoogle Scholar
and A.S. Orange
, Electrical resistivity changes in saturated rocks during fracture and frictional sliding, J. Geophys. Res.
, 1433–1445, 1968a.CrossRefGoogle Scholar
and A.S. Orange
, Further studies of the effects of pressure on electrical resistivity of rocks, J. Geophys. Res.
, 5407–5420, 1968b.CrossRefGoogle Scholar
and C. Keith
, Search for changes in velocity in the La Malbaie region of Quebec, EOS, Trans. Am. Geophys. Union
, 433, 1977 (Abstr.).Google Scholar
and G.D. Garland
, Crustal loads and vertical movements near Lake St. John, Quebec, Can. J. Earth Sci.
, 711–720, 1975.CrossRefGoogle Scholar
, B.J. Kotick
, and R.D. Elliott
, Polarization analysis of natural and artificially induced geomagnetic micropulsations, J. Geophys. Res.
, 2871–2883, 1967.CrossRefGoogle Scholar
and J.E. Lilly
, Crustal movement in the Lake St. John area, Quebec, Can. Surv.
, 292–299, 1966.Google Scholar
, R.D. Kurtz
, and E.R. Niblett
, Geomagnetic depth sounding and magnetotelluric results from a seismically active region northeast of Quebec City, Can. J. Earth Sci.
, 256–267, 1977.CrossRefGoogle Scholar
, E.R. Niblett
, and R.D. Kurtz
, Changes in magnetic and telluric fields in a seismically active region of eastern Canada: Preliminary results of earthquake prediction studies, Tectonophysics
, 219–230, 1976.CrossRefGoogle Scholar
and V.A. Savll
, The St. Lawrence Valley System: A North American equivalent of the East African Rift Valley System, Can. J. Earth Sci.
, 639–658, 1966.CrossRefGoogle Scholar
and G.D. Garland
, Magnetotelluric measurments in eastern Canada, Geophys. J. R. Astr. Soc
, 321–347, 1976.CrossRefGoogle Scholar
, J. Liard
, and H. Dragert
, Canadian precise gravity networks for crustal movement studies; an instrument evaluation, Tectonophysics
, 87–96, 1979.CrossRefGoogle Scholar
and G.G.R. Buchbinder
, Second microearthquake survey of the St. Lawrence Valley near La Malbaie, Quebec, Can. J. Earth Sci.
, 2778–2789, 1977.CrossRefGoogle Scholar
, A.E. Stevens
, R.J. Wetmiller
, and R. Du Berger
, A micro-earthquake study of the St. Lawrence Valley near La Malbaie, Quebec, Can. J. Earth Sci.
, 42–53, 1973.CrossRefGoogle Scholar
and H.F. Morrison
, Electrical resistivity variations associated with earthquakes on the San Andreas Fault, Science
, 855–857, 1974.CrossRefGoogle Scholar
, R.J. Phillips
, J.H. Whitcomb
, D.M. Cole
, and R.A. Taylor
, Monitoring of time dependent electrical resistivity by magnetotellurics, J. Geomag. Geoelectr.
, 165–178, 1976.CrossRefGoogle Scholar
, La Malbaie structure, Quebec—A Palaeozoic meteorite impact site, Meteoritics
, 1–24, 1968.Google Scholar
, Zones of shock metamorphism at the Charlevoix impact structure, Quebec, Bull. Geol. Soc. A
, 1630–1638, 1975.CrossRefGoogle Scholar
, Nouvel impact meteoritique fossile? La structure semicirculaire de Charlevoix. Can. J. Earth Sci.
, 1305–1317, 1968.CrossRefGoogle Scholar
, F.X. Bostick
, and H.W. Smith
, The estimation of magnetotelluric impedance tensor elements from measured data, Geophysics
, 938–942, 1971.CrossRefGoogle Scholar
, Earthquakes of eastern Canada and adjacent areas 1534–1927, Publ. Dom. Obs..Ottawa
, 271–301, 1962.Google Scholar
, Earthquakes of eastern Canada and adjacent areas 1928–1959, Publ. Dom. Obs., Ottawa
, 87–121, 1966.Google Scholar
, An amplifier and filter system for telluric signals, Publ. Earth Phys. Branch, Ottawa
, 1–5, 1972.Google Scholar
, P.H. Serson
, and P.A. Camfield
, A solid state electrical recording magnetometer. Publ Earth Phys. Branch, Ottawa
, 67–80, 1970.Google Scholar
and A.C. Hamilton
, Further analysis of vertical crustal movement observations in the Lac St. Jean area, Quebec, Can. J. Earth Sci.
, 1139–1147, 1972.CrossRefGoogle Scholar
© Center for Academic Publications Japan 1979