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doi:10.2204/iodp.proc.344.205.2016

Introduction

The objective of the Costa Rica Seismogenesis Project (CRISP) was to understand the processes that control fault zone behavior during earthquake nucleation and rupture propagation in an erosional subduction zone (see the “Expedition 344 summary” chapter [Harris et al., 2013a]; Expedition 334 Scientists, 2012a). To achieve a comprehensive seismogenesis study, a transect was drilled from the incoming plate to the overriding plate in a single subduction system. The CRISP drilling sites are located offshore west of the Costa Rica convergent margin, which was previously identified as a site of subduction erosion (see the “Expedition 344 summary” chapter [Harris et al., 2013a]; Vannucchi et al., 2004) (Fig. F1). This area is characterized by a low sediment supply, fast convergence rate, abundant plate interface seismicity, and changing subducting plate relief along strike (see the “Expedition 344 summary” chapter [Harris et al., 2013a]; Expedition 334 Scientists, 2012a). The incoming plate is regarded as vital to seismogenesis at this location because of the variability of the subducted components (materials derived from the subducting Cocos Ridge). During the first phase of CRISP drilling (Integrated Ocean Drilling Program [IODP] Expedition 334), basement rocks were recovered from Hole U1381A. During the second phase of CRISP (IODP Expedition 344), basement rocks were recovered from both Holes U1381C and U1414A. Here we report major and trace element and Sr-Nd-Pb isotope compositions for basement rocks collected from the two sites (U1381 and U1414) drilled on the incoming plate during Expeditions 334 and 344 (Fig. F1).

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