Plan and technological difficulties on NanTroSEIZE long term borehole monitoring system

摘要

IODP (Integrated Ocean Drilling Program) scientific drilling proposal 603 (NanTroSEIZE: Nankai Trough Seismogenic Zone Experiment) not only proposes drilling, coring, geological analyzing, and geophysical logging, but also mandates that several long term borehole monitoring systems (LTBMS) should be installed at Nankai trough, where we expect to encounter the mega splay fault and the locked region of mega thrust fault, respectively, in order to understand on the dynamics of seismogenic zone. Borehole is not mere relic after core sampled, but should be sufficiently utilized as the scientific legacy hole to monitor the interior of the Earth. The advantage of LTBMS is to simultaneously manage precise monitoring on various parameters at multiple layers in the same borehole. Its technological difficulties are hiding in establishing the reliable and robust system against deploying long and narrow structure into tiny borehole through the ocean current from the heaving surface vessel. Also, for deeper penetration, higher temperature and pressure cause many problems on the system. This paper describes the plan of NanTroSEIZE LTBMS and its technological difficulties including some results on our development.