Instrumentation Centers: Lamont-Doherty Earth Observatory A. Barclay, J. Gaherty, M. Tolstoy Scripps Institution of Oceanography J. Babcock, A. Harding, G. Kent, J. Orcutt Woods Hole Oceanographic Institution J. Collins, K. Peal, B. Wooding Oversight Committee: Doug Toomey, Chair, U. Oregon Gail Christeson, UTIG Rob Dunn, U. Hawaii Jim Fowler, IRIS Francis Wu, SUNY-Binghamton Funded by the NSF, Marine Geology and Geophysics Program

Enhancement of the OBSIP Pool for Amphibious Experiments Contour interval 1000 m

Amphibious Experiments Present Major Challenges for OBS Deployments Shallow Water Deployment (<1000 m) Trawling Biofouling Current-induced noise (all depths) Reliability Contour interval 500 m

Timeline Contour interval 500 m April: Early discussions with NSF Early May: OC consults with ad hoc science group Mid May: Earthscope meeting Mid-late May: OC report to IICs and NSF the results of the above discussions, via and conference call and prepares request for bids (RFB). June 1: IICs respond to request for bids, providing costs estimates and delivery schedule to OC. June 5: OC (does not) report to NSF. Begs for delay until after this meeting. By July 10: External panel reviews RFBs and reports to NSF. Summer 2010: Initial Cascadia deployment

Cascadia Amphibious Array: First Guess The backbone of the effort should consist of intermediate-band instruments deployed to mirror the onshore array. Assuming that the coast defines the edge of the onshore array, this would consist of 3 north-south columns of instruments extending to roughly 200 km offshore. We should also plan for a “flex” array capability to focus on smaller targets with dense spacing, probably to consist of a mix of intermediate-band and short-period instruments. Determining the mix of instruments for the flex array will consider both Cascadia and future amphibious experiments. Contour interval 500 m The OC consulted with the scientific community in order to obtain guidance on the types, capabilities and numbers of OBSs to build for Cascadia as well as future amphibious experiments.

General description of amphibious array It is very desirable to bury (or shield) sensors at intermediate-water sites to improve data quality. Trawl resistant OBSs are a must for shallow-water sites, and may mitigate noise due to currents. Trawl resistant instruments may require an ROV for recovery and possibly deployment. It may be desirable to equip some OBSs with APGs in order to detect vertical deformation. It may be desirable to equip some OBSs with accelerometers. Contour interval 500 m

Shallow water (<1000 m) requires trawl resistant mounts Shallow Water Intermediate Water ~ km Typical Cascadia Profile This is doable in terms of repackaging. May have implications for operations and ship-time, depending on water depth.

Burial improves performance Collins et al., 2001 Horizontal components on buried seismometer (red traces) are much less noisy at long periods than the horizontal components of an identical seismometer sitting on the seafloor (blue traces).

Burial/Shielding improves performance

Intermediate water ( m): Examples of shielding Not all have been tested.

Prototypes for Burial Burial has not been well tested. High risk, high payoff

Existing broadband instruments: Shielding or burial not implemented SIO BB WHOI BBLDEO BB Advantages: Less risk in delivery Known design Disadvantages: No shielding/burial Not trawl resistant

Intermediate band OBS Trillium Compact Broadband OBS Trillium 120 or 240 Guralp CMG3T Short-period OBS DPG APG Accelerometer Other Considerations Sensor configurations Leveling of sensor

Cost per Unit Instrument Type Shallow Water <1000 m Intermediate-water m Intermediate Band OBS w/ DPG$60-80K$60-70K Intermediate Band OBS w/ APG$65-95K$65-85K Broadband OBS w/ DPG-$70-100K Broadband OBS w/ APG-$75-110K Short period OBS$40-55K Addition of accelerometerAdd $5-20K

Delivery Schedule Delivery of instruments for the 2010 field season will be a challenge. LDEO: 1 per week beginning Jan by April for beginning of testing, at-sea certification. SIO: Anticipates building fleet by summer of Faster if unmodified broadband instruments. Non- specific schedule. WHOI: No schedule given.

What will our recommendations address? What types of instruments should be procured (e.g., short period, broadband, sensor types)? What is the optimal spacing of instruments given the scientific objectives? Should some of the instruments be buried to achieve better data quality? Are shallow water deployments required, if so can they be made trawl resistant and at what cost? What is the cost of each type of instrument? What is the delivery schedule? These are just some of the issues that we are considering. They are provided here to give you an idea of what to start thinking about.