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doi:10.2204/iodp.proc.334.201.2014

Introduction

The Costa Rica Seismogenesis Project (CRISP) was designed to understand the processes that control fault zone behavior during earthquake nucleation and rupture propagation at erosional subduction zones. The CRISP study area, located offshore the Osa Peninsula of Costa Rica, is part of the active and long-lived subduction erosion from Guatemala to Costa Rica (Ranero et al., 2000; Ranero and von Huene, 2000; Vannucchi et al., 2004). This area is characterized by low sediment supply, fast convergence rate, abundant plate interface seismicity, and a change in subducting plate relief along strike (see the “Expedition 334 summary” chapter [Expedition 334 Scientists, 2012a]). Arcward of the trench, the lower slope consists of a 10–12 km wide frontal prism where a modern sediment apron overlies older sediments that may have been deposited on an older fore-arc basin setting. The first phase of this project focuses on sampling of sediments, fluids, and crustal rocks to fully characterize the eroding material before subduction.

A fundamental component of our understanding of the subduction input focuses on sampling sediments, fluids, and crustal rocks because fluids and associated diagenetic reactions affect hydrological parameters (e.g., permeability and pore pressure) and may regulate the mechanical state of the plate interface at depth. Because of time constraints imposed by a short expedition with high recovery and the importance of fully constraining the fluid regime during Integrated Ocean Drilling Program (IODP) Expedition 334, we concentrated our efforts on collecting samples for postcruise studies, and only a limited number of analyses was carried out onboard. Here we report on the concentration of minor elements of samples collected from coring at two slope sites (Site U1378 on the middle slope and Site U1379 on the upper slope) and at one site on the Cocos plate (Site U1381) (Fig. F1). These data were used to complement geochemical interpretations based on shipboard results from a second IODP expedition (344) to this margin in 2012 (Harris, Sakaguchi, Petronotis, and the Expedition 344 Scientists, 2013) and strontium isotopic analyses of fluids collected during both Expeditions 334 and 344 (Ross et al., submitted).

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