As part of the 2009 ARRA (American Recovery and Reinvestment Act) spending, NSF?s Earth Sciences (EAR) and Ocean Sciences (OCE) divisions each received $5M in facility-related investment. The funds were targeted toward the creation of an Amphibious Array Facility to support EarthScope and MARGINS science objectives. The first of these studies will take place in Cascadia (offshore northern California, Oregon, Washington and southern British Columbia), where there is significant risk of a major subduction zone, ?megathrust? earthquake that will affect population centers including Vancouver, Seattle and Portland. With the primary aim of improving our understanding of seismicity and seismic risk in this region, 60 or more Ocean Bottom Seismographs (OBS) will be deployed across the region over a period of four years beginning in the summer of 2011. The recent earthquake and tsunami in northern Japan, a setting not unlike Cascadia, provide fresh impetus for this study. Good bathymetric data are essential for choosing OBS station locations. Because many of the deployments occur in and near active canyon systems and very seismically active areas, site selection will be difficult, and good bathymetric data are required to minimize the loss of instruments. The proposed cruise will fill in poor bathymetric coverage in Cascadia, particularly along the Washington and Canadian margins. In addition to its obvious contribution to the overall objective of the Cascadia Initiative, broader impacts of this effort include improvements in regional bathymetric coverage that will significantly improve our understanding of the Cascadia subduction margin, and have implications for seismic hazards in the western U.S. Additionally, the project will provide training and support for a graduate student.
As part of the 2009 Stimulus or ARRA (American Recovery and Reinvestment Act) spending, NSF’s Earth Sciences (EAR) and Ocean Sciences (OCE) divisions each received $5M in facility-related investment. The funds were targeted toward the creation of an Amphibious Array Facility to support EarthScope and MARGINS science objectives. The initial emphasis and deployment site was onshore/offshore studies of the Cascadia margin, with an expectation that the facility would later move to other locations. Addressing the offshore region, The Cascadia Initiative funded the construction of a total of 60 Ocean Bottom Seismometers (OBSs) by the three Institutional Instrument Contributors (IICs) of the National Ocean Bottom Seismometer Instrumentation Pool (OBSIP). The overall purpose if the deployment is the investigation of the Cascadia subduction margin and ridge system as a whole, a new approach embraced in recent years by EarthScope and OOI. Good bathymetric data are essential for siting OBS station locations and ensuring the best chance of the instruments settling to the bottom in relatively smooth flat areas with a good chance of recording fidelity. Equally important is to deploy instruments in areas where the topographic, structural, and hydrologic context is reasonably well understood, so that a maximum number of instruments will be recovered from each deployment, and so that analysis of the signals will benefit from understanding the topographic and structural settings for each instrument. Some of the CI deployed instruments will be located on the abyssal plain of the Juan de Fuca plate, and are relatively safe from local geohazards. However, this initiative specifically addresses the Cascadia subduction boundary, and thus most of the instrument deployments are on the continental margin of this very dynamic plate boundary. Because many of the deployments are planned to span a number of active canyon systems and very seismically active areas, site selection will be difficult, and good bathymetric data are also required to prevent a number of instruments from being swept into channels and canyons and lost or damaged during the deployment. The primary goal of the project was to the extent possible, remedy the poor bathymetric coverage in Cascadia, particularly along the Washington and Canadian margins for the safely of the instruments, and will also substantially improve our scientific context for future work in Cascadia expected under GeoPrisms and OOI. This project had several outcomes beyond the original goals. One of these was the creation of the best possible bathymetric surface as a "before" picture, prior to the coming great earthquake. Following a great thrust earthquake, it will be possible to re-survey the area and difference the new grid with the current one to assess the difference in three dimensions. This was done to some extent off Tohoku following the March 2011 earthquake, but that effort, while successful, was limited to a few swaths. Our hope is that a broad surface will be available for comparison in Cascadia. These data also will form the basemap for other Cascadia studies conducted as part of the Cascadia Initiative, and the GeoPrisms Programs, and well as other investigations for many years to come. A second outcome is that improvements in regional bathymetric coverage will significantly improve our understanding of the Cascadia subduction margin, and will have implications for seismic hazards in the western U.S. The new bathymetric surface has already been incorporated into three papers, one published and two in preparation, which deal with this topic. Additionally, the project provided training and support for a graduate student who is carrying on with his work to develop structural models of the accretionary prism using the products from this project, and another who is using the data for analysis of turbidity currents likely triggered by past great earthquakes. The resulting data has and is being be provided to the community through publications, national and international meetings, and public databases such as NGDC, GeoMap App, and PaCOOS.
