June 18-21, 2006
We are engaged in a study of a seafloor landslide off the coast of Santa Barbara, California. A large scar there remains from the Goleta slide, a well studied feature (1.51 km3 of failed material) that likely failed several thousand years ago. A smaller neighboring feature, the Gaviota slide (0.02 km3 of failed material), was probably triggered during the 1812 Santa Barbara earthquake. Our investigations started in 2004 with a chirp sonar survey. The survey revealed a relationship between a “crack” in the sediment propagating from the Gaviota slide’s headwall and a thrust fault clearly seen in the subsurface layers. In the next phase of our project we are applying three new time-lapse seafloor geodetic techniques that vary in spatial and temporal resolution. One method uses optical fibers stretched and buried in the sediment to monitor creep. Each cable has an optical system that measures the absolute length of the stretched optical fiber with a precision of 1 mm every hour. The cables vary in length from 250 m to 750 m. A second system consists of an array of precise acoustic transponders on the seafloor interrogated by several buoyantly suspended command nodes. Offshore engineering tests of these reveal a precision of 5 mm over baselines up to 2 km. Finally, we are developing an AUV-borne precision mapping capability that promises to provide a monitor of seafloor shape changes that occur over tracklines of many kilometers in length with a precision goal of 10 cm. We are currently preparing these geodetic monitoring tools for deployment across a presumed future headwall near the Gaviota slide in a nested fashion to provide redundancy and a means to compare resolutions.
Mark Zumberge, Jeff Babcock, Hugh H. Banon, John Blum, C. D. Chadwell, Jeff Dingler, Neal Driscoll, Gerald D'Spain, Philippe Jeanjean, Graham Kent, Graham Openshaw, and John Orcutt, "Studies of the Gaviota Slide Offshore Southern California" in "Geohazards", Professor Farrokh Nadim, International Centre for Geohazards, Oslo, Norway; Dr. Rudolf Pöttler, Managing Director, ILF - Consulting Engineers, Innsbruck, Austria; Professor Herbert Einstein, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA; Professor Herbert Klapperich, TU Bergakademie Freiberg, Institut für Geotechnik, Freiberg, Germany; Professor Steven Kramer, University of Washington, Seattle, Washington, USA Eds, ECI Symposium Series, (2006). http://dc.engconfintl.org/geohazards/26