NEPTUNE Canada

Monitoring crustal formation pressures using CORKs

Away from their boundaries Earth's tectonic plates move steadily, but near plate boundaries, motions are episodic. Stresses that accumulate over years, decades or even centuries, are released as sudden earthquake-generating slips. These events change the hydrology of the surrounding crustal rock, as it is squeezed and shaken by tectonic forces. Strain-induced pressure changes can be observed hundreds of kilometers from earthquake centres.

Geoscientists are using Circulation Obviation Retrofit Kits (CORKs) to study tectonic activity in the Cascadia subduction zone. CORKs are installed in boreholes extending tens to hundreds of metres into the igneous seafloor through a sediment cover of several hundred metres. Pressure changes at the borehole can be used to determine the magnitude of slip and corresponding efficiency with which earthquakes may be generated.

At site ODP 1027, NEPTUNE Canada will initially connect to two existing Ocean Drilling Program borehole monitoring systems (CORKs were instrumented there in 1996 and 2002). Upgraded CORK data logging units will feature:

1. increased sensor resolution for a more detailed view of the plate-scale processes at work
2. compatibility with NEPTUNE Canada's power and data transmission network

These upgrades will enable nearly continuous measurement, helping scientists to better understand the interconnections between hydrologic, geodynamic and seismic processes in Earth's plates.

With the new-found ability to study active plate tectonic processes, seismogenic slip, and related fluid flow using seafloor hydrologic instrumentation, comes new motivation to increase the rate with which information can be gathered. Towards these ends, we have built new 

• Plugging the Seafloor with CORKs: A window into the plumbing system hidden beneath the ocean's floor (Oceanus Magazine, v.42, No.1, 2000)
• Using ODP Boreholes for Studying Sub-seafloor Hydrogeology: Results from the First Decade of CORK Observations (Geoscience Canada, v.28, No.4, 2001)