Plate Tectonics is the notion that the Earth?s surface is comprised of large plates that form at mid-ocean ridges and are consumed by the process of subduction, largely near the margins of ocean basins. The plate tectonic model explains many observable phenomena, including the distribution of great earthquakes and violent volcanic eruptions. A central assumption of plate tectonic theory is that the plates are rigid. This assumption applies to most of the Earth?s surface, but there are exceptions. One exceptional region is the Gorda Basin, which is located west of northern California and southern Oregon. There is compelling evidence that the seafloor in this region is actively deforming ? including the occurrence of numerous earthquakes ? but just how the seafloor is deforming and why has eluded unambiguous interpretation for several decades. This deployment of Ocean Bottom Seismographs (OBS) has the objective of yielding a more detailed picture of earthquake seismicity in the Gorda Basin, and thereby resolving the manor and cause of the deformation. There is added interest in this problem because the Gorda Basin is being actively subducted beneath the adjacent continent, where major ?megathrust? earthquakes are known to have occurred. How deformation of the Garda Basin affects the potential for large damaging earthquakes in this region is unknown, but of considerable societal interest. An added broader impact of this project is that the deployment of OBSs for this project will supplement the Cascadia Initiative, an amphibious deployment of OBSs offshore and seismic stations onshore. A principal aim of the Cascadia Initiative is to develop a better understanding of seismicity and of megathrust earthquake risk along the Cascadia margin, which extends from northern California to southern British Columbia.
