SZO Seminar Notes – May 27, 2015: The merits of deep drilling


Slow and delayed deformation and uplift of the outermost subduction prism following ETS and seismogenic slip events beneath Nicoya Peninsula, Costa Rica Discussion leader: Will Wilcock
Paper: Davis, E.E., H. Villinger, and T. Sun (2015), Slow and delayed deformation and uplift of the outermost subduction prism following ETS and seismogenic slip events beneath Nicoya Peninsula, Costa Rica, Earth and Planet. Sci. Letts., 410, 117-127.

IODP is international consortium, with ~40 countries, with 3 science themes that can be addressed with deep drilling.  Has multiple platforms (ships); the JOIDES Resolution (NSF owned) is ‘riserless’ (drilling cuttings don’t get saved – dumped on seafloor), the Chikyu (Japanese owned) employs riser drilling in which drilling fluid and cuttings come back up to the ship.  Riser drilling is safer and thus can be done to greater depths and higher pressures.

JOIDES Resolution regions targeted for the next 5 years are oceans that have not previously been drilled.  Since the Pacific has been drilled, it will be 5-10 years before any further drilling is done there.  To date the Chikyu has only drilled around Japan, but is scheduled already for the coming decade.


Experiments have been attempted to test the improvement in signals and practical feasibility of borehole seismometer deployments.  Early failures in the late 1990s basically killed any will to do further development.  The borehole signals were significantly quieter (20-30 db) than those at the surface or buried a few meters.


With offshore acoustic GPS could discriminate between different locking models.  Can also use dilatation to measure secular and transient deformation, by deploying pressure sensors in boreholes.


CORK plugs a borehole so you can measure the pressures at various depths in a borehole, below where the borehole is cased.  Can also be used to sample fluids (e.g. for biological studies).  Many were deployed early on in mid-plate regions just to understand circulation through the shallow crust.  They’re very sensitive to earthquake-generated dilatation/contraction, but sorting out deformation from hydrologic response is challenging.  Can also see secular and transient strains.


Currently there are 3 sites offshore Cascadia where acoustic GPS is being measured.  New sensors are being added to the Canadian cabled observatory. 


At the recent drilling meeting drilling was proposed  offshore central Oregon (hydrate ridge, span deformation front), central Washington (span deformation front, where surface faults dip opposite way), and Vancouver Island near the cable.  In Cascadia it is impossible to drill to base of the sediments because of their great thickness.