OCEANIC ELECTRIC CURRENTS, GEOMAGNETIC VARIATIONS AND THE DEEP ELECTRICAL CONDUCTIVITY STRUCTURE OF THE OCEAN-CONTINENT TRANSITION OF CENTRAL CALIFORNIA

The variations of electromagnetic field components along a line across central California have been examined in the frequency range .125 to 4 cph by means of an array of stations extending from 320 km inland to 630 km offshore. The three components of the magnetic variations were recorded at six lan...

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Bibliographic Details
Main Author: Filloux,Jean H
Format: Report
Language:English
Subjects:
CONDUCTIVITY
DEPTH FINDING
ELECTRIC FIELDS
ELECTROMAGNETIC FIELDS
Geomagnetism
MAGNETIC PROPERTIES
MAGNETOMETERS
NUMERICAL ANALYSIS
OCEAN BOTTOM
OCEAN CURRENTS
OCEANS
Physical and Dynamic Oceanography
PRESSURE
ROCK
TEMPERATURE
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Summary:The variations of electromagnetic field components along a line across central California have been examined in the frequency range .125 to 4 cph by means of an array of stations extending from 320 km inland to 630 km offshore. The three components of the magnetic variations were recorded at six land positions. Simultaneously, records of the oceanic electric field in a direction approximately parallel to the coast were obtained at three stations located as far as 150 km offshore by using self-contained recorders installed on the sea floor. The cross-correlation of all field components leads to field relationships suggesting a large-scale, nearly two-dimensional structure of the electrical conductivity of the earth's crust and upper mantle in a region adjacent to the California coast. Estimates of the continental and oceanic conductivity distribution with depth were carried out by solving numerical models. The estimate of the offshore conductivity profile based on models of the coastal cross section are in excellent agreement with the independent magnetotelluric sounding. In the light of the present knowledge of the properties of rocks at high pressure and temperature, the high electrical conductivity of the oceanic basement favors a highly basaltic external mantle shell, extending to no less than 30 km below the Mohorovicic discontinuity. (Author)