The electrical conductivity distribution beneath Vancouver Island: A region of active plate subduction

Journal Article · Tue Jul 10 00:00:00 EDT 1990 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JB095iB07p10929· OSTI ID:5456197

Kurtz, R D; Gupta, J C ^[1]; DeLaurier, J M ^[2]

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1. Geological Survey of Canada, Ottawa, Ontario (Canada)
2. Geological Survey of Canada, Sidney, British Columbia (Canada)

Magnetotelluric (MT) and geomagnetic depth sounding (GDS) data were recorded at 25 locations across Vancouver Island, Canada, over the subducting Juan de Fuca plate. The GDS data respond to a number of local conductive features at frequencies above 10 Hz while at longer periods, the in-phase and quadrature induction arrows are colinear and are aligned approximately normal to the continental shelf with a maximum amplitude response near the southwest coast. Interpretation of the MT data show the presence of a conducting zone at depths greater than 20 km beneath Vancouver Island and correlating with a strong seismic reflector. Extensive testing with two dimensional models shows the MT and GDS data are consistent with a proposed geoelectrical structure containing a conducting layer extending from the Pacific Ocean, dipping beneath Vancouver Island, and in electrical contact with the mainland conductive region. The layer has a horizontal conductance of 200 S that may decrease to 100 S beneath the northeast side of Vancouver Island. Related geophysical studies suggest the conductive zone is above the actual thrust surface of the Juan de Fuca plate. The conducting layer is most likely the result of cracks and pores filled with saline fluids which are supplied by water subducted with the oceanic crust and by dehydration reactions. The presence of fluids has significant implications for thrust earthquakes and for metamorphic reactions that occur in subduction zones. The conductance of the upper mantle (between 90 and 390 km) is best modeled at approximately 1,500 S.

• OSTI ID: 5456197
• Journal Information: Journal of Geophysical Research; (United States), Vol. 95:B7; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
BRITISH COLUMBIA
SUBDUCTION ZONES
ELECTRIC CONDUCTIVITY
CONTINENTAL SHELF
DEPTH
DISTRIBUTION
EARTHQUAKES
GEOLOGIC FORMATIONS
GEOLOGIC FRACTURES
GEOLOGIC MODELS
GEOMAGNETIC FIELD
GEOPHYSICAL SURVEYS
ISLANDS
MAGNETIC SURVEYS
MAGNETOTELLURIC SURVEYS
PLATE TECTONICS
POROSITY
RESERVOIR FLUIDS
SALINITY
TWO-DIMENSIONAL CALCULATIONS
CANADA
CONTINENTAL MARGIN
DEVELOPED COUNTRIES
DIMENSIONS
ELECTRICAL PROPERTIES
ELECTRICAL SURVEYS
ELECTROMAGNETIC SURVEYS
FLUIDS
GEOLOGIC STRUCTURES
MAGNETIC FIELDS
NORTH AMERICA
PHYSICAL PROPERTIES
SEISMIC EVENTS
SURVEYS
TECTONICS
580000* - Geosciences