IRIS Exhibits OBS at AGU

There was no shortage of cool new innovative products at AGU this year- Nanometrics rolled out borehole versions of its Trillium 120 and Compact. Metrozet answered the Trillium Compact’s success with the “Mini Broadband Seismometer”. gempa introduced HTML-based GUIs for SeisComP. Vaisala showed off the all-in-one weather sensors that are popular with UNAVCO. Space geeks played with model NASA rovers. Even sleek yellow autonomous ocean gliders were on display. But Scripp’s ABALONES Ocean Bottom Seismometer (OBS) stole the show for me:

Scripps Institute of Oceanography ABALONES Ocean Bottom Seismometer (used in the Cascadia Initiative- for complete details visit obsip.org)

Scripps Institute of Oceanography ABALONES Ocean Bottom Seismometer (used in the Cascadia Initiative- for complete details visit obsip.org)

Spear-headed by Brent Evers in Washington, D.C., the IRIS managed Ocean Bottom Seismograph Instrument Pool (OBSIP) is pushing seismology overboard into new frontiers. When some of us look at a map of the Global Seismic Network we see a big gap in China. Brent and his team see things a little differently. They see oceans of space between sensors. But that is slowly changing. The National Science Foundation, known for its lavish spending on projects that push into new frontiers, has joined forces with the technical and instrumental expertise at the Lamont-Doherty Earth Observatory, Scripps Institute of Oceanography, Woods Hole Oceanographic Institution and IRIS to deploy OBS’s all over the globe. Passive experiments are ongoing west of Cascadia and at the Marianas trench. Many active-source experiments are also underway. You can track the progress of these and other OBS experiments by visiting: http://www.obsip.org/experiments/experiment-map/.

Jessica Lodewyk of OBSIP gave me a tour of Scripps’ latest OBS design. A beefed-up Nanometrics Trillium capable of withstanding 5 kilometers of ocean pressure sits inside a giant yellow buoy:

The Nanometrics Trillium Ocean Bottom Seismometer

The Nanometrics Trillium Ocean Bottom Seismometer

Jessica explained that the buoy sinks and is held fast to the ocean floor by heavy steal plates. Once the experiment is completed, a vessel can call the OBS to the surface by sounding a specific frequency that, when detected by the OBS’s hydrophone, triggers the severing of the cable that affixes the buoy to the metal weight and the whole unit rises to the surface:

Hydrophone mounted to the surface of the OBS (for display purposes only)

Hydrophone mounted to the surface of the OBS (for display purposes only)

Once surfaced, the Iridium beacon begins blinking and sending sms/email to the crew:

Novatel Iridium Beacons

Novatel Iridium Beacons

Data from all experiments is archived at the IRIS DMC. As the seismometers are installed at 100s to 1000s of meters depth, the orientation of the horizontal components is unknown. IRIS recommends using Stachnik et al. 2012’s Rayleigh-Wave Polarization method to correct the data.

The OBSIP currently has 160 broadband and 93 short-period instruments on hand and ready to walk the plank.

–Branden

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