3 research outputs found
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
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 JOIDES Resolution 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.-1 possibly caused by on-land uplift triggered
by the subduction of the Cocos Ridge. The geochemical
data as well as the in situ 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 in situ 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)