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doi:10.2204/iodp.sp.334.2010

Introduction

The key objective of the Costa Rica Seismogenesis Project (CRISP) is to understand the physical processes that generate earthquakes. This could be achieved through drilling the seismogenic zone and long-term near-source monitoring of this dynamic environment. During the past three decades, the tectonically active near-trench areas of convergent margins have been drilled several times. However, natural hazards relevant to society such as earthquakes, tsunamis, and volcanism occur in parts of the subduction system that are too deep to be directly sampled by conventional drilling technology. The improved capabilities of IODP allow exploration of the seismogenic zone, which is a primary scientific objective highlighted in the Initial Science Plan for IODP. The Central American margin offshore the Osa Peninsula of Costa Rica is a region where the processes that lead to the onset of seismicity can be addressed because of the abundant earthquake activity and because the seismogenic zone is within the operational capabilities of the IODP riserless drillship and the D/V Chikyu (riser drillship).

Expedition 334 is based on part of IODP Proposal 537A-Full5 (CRISP Program A). This expedition will focus on constraining the boundary conditions of lithology, fluid flow, and thermal structure that trigger unstable slip in the seismogenic zone along a drilling transect at two sites (CRIS-3B and CRIS-4A; Fig. F1, F2) which will serve as pilot holes for future riser drilling (CRISP Program B). CRISP Program B aims to reach the plate boundary, observe physical conditions, and sample fault zone material before and after the onset of seismogenic behavior of large earthquakes.

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