Scientific objectives

Operations at proposed Site NT1-03B will penetrate the frontal thrust, and those at proposed Site NT2-01B will target the shallow portion of the megasplay fault system, just seaward of the break in slope marking the boundary between the inner and outer accretionary wedge (Figs. F3, F4). At both sites, drilling will continue sufficiently far into the footwall sediments to fully characterize them. The overall scientific objectives at Sites NT1-03B and NT2-01B are to understand the following:

Structural observations of cores, particularly in and surrounding the fault zone, will be of primary importance in characterizing the nature of slip and the past evolution of the splay fault. These observations will be integrated with imaging using the computed tomography scanner and downhole visualization logs collected during Expedition 314 (LWD Transect) and wireline logging. Core descriptions and physical property observations will characterize the consolidation state of the hanging wall and footwall and yield insight into the displacement history along the splay fault and the fluid response to fault slip. The shipboard physical property measurements will help ground-truth data from Expedition 314 (LWD Transect) and wireline logging. Age determinations above and below the fault will be extremely important to estimate displacement.

A further scientific objective is to understand the relationship between fluid behavior and slip and deformation:

  • How do fluid pressure and consolidation state influence fault zone slip?
  • Do fault zones provide conduits for fluid flow from depth?

Geochemical observations will provide important information on fluid flow within and surrounding the fault zones. For example, detailed characterization of veins can yield information on past fluid flow, whereas pore fluid anomalies along the fault zone are potential indicators of recent fluid flow. Temperature measurements, through in situ probes and wireline logging, provide information on background thermal gradient, which controls diagenetic reactions and can indicate areas of very rapid fluid flow from depth. Estimation of pore pressure is important to the scientific objectives; although in situ probe measurements have not yet been developed for the Chikyu, porosity will provide an indirect constraint. In addition, geotechnical tests on cores will provide data on consolidation state.