The authors describe a new approach to the problem of active source electromagnetic sounding at sea and give initial results from its first use, across a mid-ocean ridge crest-the East Pacific Rise at 13 degrees 10'N. The electromagnetic energy is generated by a 100 m horizontal electric dipole of moment 6000 Am, which is towed close to the sea-bed. Square-waves with frequencies from 1/4 Hz and 8 Hz are transmitted and these propagate through the, generally, more resistive lithospheric half of the ocean-seafloor interface. The receivers are remotely operating sea bottom instruments, each equipped with an orthogonal pair of 12 m horizontal electric antennae. Electric fields of the order of 10-10 V/m are measured. Initial results show porosities of 30% or more at 30 m below the seafloor decreasing to less than 5% at a depth of 1 km. No intrinsic difference is observed between the upper crustal conductivity structure of the rise axis and that of 100000 year old crust.
Active source electromagnetic technique for conductivity profiling below the seafloor
Eine elektromagnetische Messtechnik mit aktiver Quelle für Leitfähigkeitsprofile unterhalb des Meeresbodens
IEE Colloquium on 'Monitoring the Sea' ; No.182 ; 4/1-4/5
1990
, 8 Quellen
Conference paper
English
NEW OPPORTUNITIES FOR OCEAN RESEARCH: FROM THE SURFACE TO BELOW THE SEAFLOOR
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