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doi:10.2204/iodp.proc.344.207.2017

Introduction

The study region of the Costa Rica Seismogenesis Project (CRISP), located offshore the Osa Peninsula, is part of an extensive erosional subduction zone, spanning from Guatemala to Costa Rica (Ranero and von Huene, 2000; Ranero et al., 2000; Vannucchi et al., 2004). The CRISP drilling project was aimed at understanding the processes that control fault zone behavior during earthquake nucleation and rupture propagation at erosional subduction zones. This region is characterized by low sediment supply, fast convergence rate, abundant seismicity, and change in subducting plate relief along strike (see the Expedition 344 summary chapter [Harris et al., 2013a]). Arcward of the trench, the lower slope consists of a 10–12 km wide frontal prism, where a modern sediment apron overlies older sediment that may have been deposited in a forearc basin setting (Ross et al., 2015). Five sites were drilled, three on the overriding and two on the incoming plates (Fig. F1).

Pore fluids were subsampled and analyzed for Cl, K, Rb, and Cs concentrations at the five sites drilled during Expedition 344, and the results are reported below (Table T1; Figs. F2, F3, F4, F5, F6).

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