Instrumentation Centers:

Lamont-Doherty Earth ObservatoryA. Barclay, J. Gaherty, M. Tolstoy

Scripps Institution of OceanographyJ. Babcock, A. Harding, G. Kent, J. Orcutt

Woods Hole Oceanographic InstitutionJ. Collins, K. Peal, B. Wooding

Oversight Committee:

Doug Toomey, Chair, U. OregonGail Christeson, UTIG Rob Dunn, U. HawaiiJim Fowler, IRISFrancis Wu, SUNY-Binghamton

Funded by the NSF, Marine Geology and Geophysics Program

www.obsip.org

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 e-mail 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 WaterIntermediate

Water

~50-100 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 (1000-5500 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 BB LDEO 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 TypeShallow Water

<1000 m

Intermediate-water 1000-

5500 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 $40-55K

Addition of accelerometer Add $5-20K Add $5-20K

Delivery Schedule

Delivery of instruments for the 2010 field season will be a challenge.

LDEO: 1 per week beginning Jan. 2010. 10 by April for beginning of testing, at-sea certification.

SIO: Anticipates building fleet by summer of 2010. 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.