Abstract
The Costa Rica Seismogenesis Project (CRISP) is an experiment to understand the processes that control nucleation and seismic rupture of large earthquakes at erosional subduction zones. Integrated Ocean Drililng Program (IODP) Expedition 334 by R/V <i>JOIDES Resolution</i> is the first step toward deep drilling through the aseismic and seismic plate boundary at the Costa Rica subduction zone offshore the Osa Peninsula where the Cocos Ridge is subducting beneath the Caribbean plate. Drilling operations included logging while drilling (LWD) at two slope sites (Sites U1378 and U1379) and coring at three slope sites (Sites U1378–1380) and at one site on the Cocos plate (Site U1381). For the first time the lithology, stratigraphy, and age of the slope and incoming sediments as well as the petrology of the subducting Cocos Ridge have been characterized at this margin. The slope sites recorded a high sediment accumulation rate of 160–1035m m y<sup>&minus;1</sup> possibly caused by on-land uplift triggered by the subduction of the Cocos Ridge. The geochemical data as well as the <i>in situ</i> temperature data obtained at the slope sites suggest that fluids are transported from greater depths. The geochemical profiles at Site U1381 reflect diffusional communication of a fluid with seawater-like chemistry and the igneous basement of the Cocos plate (Solomon et al., 2011; Vannucchi et al., 2012a). The present-day <i>in situ</i> stress orientation determined by borehole breakouts at Site U1378 in the middle slope and Site U1379 in the upper slope shows a marked change in stress state within ~12 km along the CRISP transect; that may correspond to a change from compression (middle slope) to extension (upper slope). <br><br> doi:<a href="http://dx.doi.org/10.2204/iodp.sd.15.03.2013" target="_blank">10.2204/iodp.sd.15.03.2013</a>
Highlights
Introduction andGoals and at one site on the Cocos plate (Site U1381)
(IODP) Expedition 334 by R/V JOIDES Resolution is the first hole breakouts at Site U1378 in the middle slope and Site step toward deep drilling through the aseismic and seismic U1379 in the upper slope shows a marked change in stress plate boundary at the Costa Rica subduction zone offshore state within ~12 km along the Costa Rica Seismogenesis Project (CRISP) transect; that may the Osa Peninsula where the Cocos Ridge is subducting correspond to a change from compression to beneath the Caribbean plate
For the first time the lithology, stratigraphy, and age of the slope and Subduction megathrusts are responsible for the largest incoming sediments as well as the petrology of the subduc- earthquakes on Earth and are often accompanied by devasting Cocos Ridge have been characterized at this margin. tating tsunamis
Summary
IODP Expedition 334: An Investigation of the Sedimentary Record, Fluid Flow and State of Stress on Top of the Seismogenic Zone of an Erosive Subduction Margin doi:10.2204/iodp.sd.15.03.2013 by Paola Vannucchi, Kohtaro Ujiie, Nicole Stroncik, and the IODP Exp. 334 Scientific Party. (IODP) Expedition 334 by R/V JOIDES Resolution is the first hole breakouts at Site U1378 in the middle slope and Site step toward deep drilling through the aseismic and seismic U1379 in the upper slope shows a marked change in stress plate boundary at the Costa Rica subduction zone offshore state within ~12 km along the CRISP transect; that may the Osa Peninsula where the Cocos Ridge is subducting correspond to a change from compression (middle slope) to beneath the Caribbean plate. The slope sites recorded a high sediment accumulation rate 50% of the global subduction zones (Clift and Vannucchi, of 160–1035m m.y.-1 possibly caused by on-land uplift trig- 2004), can generate magnitude 9.0 earthquakes, as shown by gered by the subduction of the Cocos Ridge. 84°W Caribbean Plate upper plate prov-enance of the material that 10° N is present along the megathrust at seismo-
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