Scientific objectives

Operations at proposed Site NT2-11B will drill, sample, and case the hole above the locked portion of the coseismically active plate boundary thrust. These operations will also provide preparation for later observatory placement, which will monitor deformation, seismicity, pore pressure, and temperature (Figs. F3, F4). The fundamental scientific objectives of Expedition 319 include:

  1. Documenting the lithology, structural geology, physical properties, and composition of the upper 1600 m of basin fill sediments in the hanging wall of the plate boundary fault;

  2. Collecting core at or near the depth of potential observatory installation to confirm stratigraphic and structural observations and interpretations made from geophysical techniques, and to obtain samples for shore-based geotechnical and mechanical analyses; and

  3. Conducting downhole tests to measure in situ pore pressures and stress states.

At proposed Site NT2-01J, drilling will penetrate the megasplay fault at 410 meters below seafloor (mbsf) and the footwall to a total depth (TD) of 525 mbsf (Figs. F5, F6). The major scientific objectives at proposed Site NT2-01J include:

  1. Characterizing the lithology and structural geology of the hanging wall, fault zone, and footwall using logging data;

  2. Defining physical properties in the hanging wall and footwall of the shallow part of the megasplay; and

  3. Installing a temporary monitoring package in a screened interval, which is designed to monitor pore pressure and temperature within the fault zone.

The overall engineering objectives at proposed Sites NT2-11B and NT2-01J are to set the wellhead, case and cement the sites in preparation for future observatory deployment, and install temporary monitoring instruments attached to a bridge plug at proposed Site NT2-01J.