12 March 2015

Andrei Swidinsky describes a transient electromagnetic survey to image the resistivity structure of the hydrate vent CNE03, offshore Mid-Norway (located approximately 10 km north of the Storegga Slide sidewall). The experiment is unique in that the electric dipole transmitter has two polarizations for each transmission station. Furthermore, the newly designed transmitter is deployed in a pogo-style acquisition, which is suitable for a detailed investigation of a small scale seafloor target. The geometry of the experiment makes conventional interpretation methods difficult so that we simplify the data by creating a single rotationally invariant quantity from the original four electric field measurements (two electric field measurements for two transmitter polarizations). This invariant is further reduced to an apparent resistivity, which is useful for rapid resistivity mapping of the seafloor. Results show that CNE03 is characterized by increased apparent resistivities which correlate well with increased P-wave velocities determined from ocean bottom seismometer measurements.

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