In May 2006, we conducted a combined magnetotelluric (MT) and controlled source electromagnetic (CSEM) survey of the Catalina Crater, located in the Inner Continental Borderland off the coast of southern California. The Catalina crater is visible in seafloor bathymetry as a circular feature 30 km in diameter, with a morphology similar to a large crater, including a raised outer rim, ring moat and a central peak. Seismic, gravity and magnetic data show similarities to known impact craters, yet enough ambiguity exists that an alternative volcanic origin cannot be ruled out. Our marine electromagnetic survey was designed to map electrical conductivity from the seafloor to 30 km depth in order to provide further constraints on the origin of the crater. We deployed a 38-kilometer line of 12 seafloor MT/CSEM receivers, extending over the eastern three quarters of the crater and out over the trough directly to the east. CSEM transmissions were performed by deep-towing the Scripps Undersea EM Source Instrument (SUESI) along a 30 km tow line over the receivers. SUESI transmitted with a 95.2 kAm source dipole moment and used a complex binary waveform consisting of fundamental frequencies of 0.1, 1, and 10~Hz. The MT data provide constraints on conductivity variations to 30 km depth and are augmented with CSEM data for imaging conductivity from the seabed to a few kilometers depth. Good quality MT responses were obtained in the period band of 5-5000 seconds and show large conductivity variations across the survey line. As a first cut interpretation of the CSEM data, we derived apparent resistivities from changes in amplitude of the recorded signal with range, and mapped the apparent resistivities into a resistivity pseudosection for each frequency. The pseudosections slice through the eastern half of the crater and the adjacent trough, providing a first-order glimpse of the lateral variations of conductivity. Our electromagnetic study of the crater will provide new insights into the crater origin by allowing us to distinguish between conductive porous sediments and resistive volcanics and basement formations.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 1515 Geomagnetic induction;
- 1599 General or miscellaneous