- © 2009 by the Seismological Society of America
Two-thirds of the Earth's surface is covered by oceans, which represents a considerable challenge to investigations of global-scale dynamic processes in the Earth's interior and of tectonic processes at ocean-continent boundaries. Long-term ocean-floor observations are also necessary to better constrain regional tectonics, such as on the western margin of North America where tectonics and seismic activity do not stop at the continental edge. In northern California, for example, the most active seismic zone is near the Mendocino triple junction and is mostly offshore, as are a number of hazardous faults such as the San Gregorio and Hosgri faults and part of the San Andreas fault. Much effort has been expended to deploy networks of seismic stations in the western United States, most recently broadband stations, with the simultaneous goals of monitoring the background seismicity, understanding modes of strain release, documenting seismic hazards, and providing constraints on crustal and upper-mantle structure. However, because there are very few offshore islands in central and northern California, practically all stations are located on the continent. As a consequence, the study of plate-boundary processes, as afforded by regional seismological investigations, is heavily skewed on the continental side of the San Andreas fault (SAF) system. Offshore seismicity is poorly constrained, both in location and in mechanisms, as is crustal structure at the edge of the continent.
The need for long-term ocean-floor seismic observatories has been widely recognized, and several national and international efforts have been striving for more than two decades to resolve the technological and logistical issues associated with such deployments and establish such observatories (e.g., Le Pichon et al. 1987; Purdy and Dziewonski 1988; Purdy 1995; Forsyth et al. 1995; Montagner and Lancelot 1995; Suyehiro et al. 2002, 2006).
In April 2002 we deployed a broadband …