DRILLING STRATEGY
In order to install the instrument string, the borehole needs to equipped with reentry cones and be cased through unstable sections. The instrument string should be located in a relatively homogeneous and unfractured zone, preferably in rocks older than early Miocene. Installation of borehole sensors will be made by the drillship. The sensor package consists of an 8-in diameter strainmeter, with two seismometers and a tiltmeter attached above it. Above the sensor, there will be nearly 1 km of support tubing or casing that runs from the sensor package to the seafloor. The sensor package will be secured to rock exposed at the base of the borehole by pumping cement through the drill string and support tubing. Afterwards, the drill string will be disconnected from the support tubing at seafloor level (Fig. 5).
To obtain volcanic ash records that will ensure complete recovery in the Pliocene and younger section, piston coring to refusal is preferred, ideally at least twice at one site. Below that, single extended core barrel (XCB) coring will be used to recover the Miocene section in the interval from ~250 to 450 mbsf. We will then switch to a rotary core barrel (RCB) bit and drill a new hole to ~450 mbsf and then core to ~1000 mbsf or deeper, if time permits.