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doi:10.2204/iodp.sp.344.2012

Introduction

The primary objective of CRISP is to better understand the processes that generate earthquakes along the subduction thrust at erosive margins. Drilling and monitoring the plate boundary provides critical data for understanding these systems. Drilling allows sampling of the sedimentary inputs, the framework rock comprising the overriding plate, and the plate boundary and measurements of fluid geochemistry, temperature, and stress. Monitoring studies provide insight as to how these systems change with time.

During the past three decades, tectonically active shallow near-trench areas of convergent margins have been drilled in several areas. These areas include Barbados (Mascle, Moore, et al., 1988; Shipley et al., 1992), the Nankai Trough (Kinoshita, Tobin, Ashi, Kimura, Lallemant, Screaton, Curewitz, Masago, and the Expedition 314/315/316 Scientists, 2009; Taira, Hill, Firth, et al., 1991), and Costa Rica (Kimura, Silver, Blum, et al., 1997; Morris, Villinger, Klaus, et al., 2003). However, to better understand natural hazards such as the generation of earthquakes, tsunamis, and arc volcanism requires drilling to the seismogenic zone. The improved capabilities of IODP allow exploration of the seismogenic zone, a primary scientific objective of the Initial Science Plan for IODP. The Costa Rica margin offshore the Osa Peninsula is a region where the processes that lead to the onset of seismicity can be addressed because of abundant seismicity and because the shallow subduction thrust is within the operational capabilities of the IODP riserless drillship (JOIDES Resolution) and the seismogenic zone is reachable with the riser drillship (D/V Chikyu).

Expedition 344 is based on IODP Proposal 537A-Full (CRISP Program A) and is the continuation of Expedition 334. Like Expedition 334, this expedition will focus on sampling the lithology, characterizing the fluids, and measuring the temperature and stress indicators that lead to a transition from stable to unstable slip. The goals of CRISP Program B are to reach the plate boundary within the seismogenic zone, observe physical conditions, and sample fault zone behavior updip and downdip of large earthquake generation.

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