IODP Exp. 334 CRISP A; overview of initial results from the Costa Rica seismogenesis experiment

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Author(s): Vannucchi, P.; Ujiie, K.
Integrated Ocean Drilling Program, Expedition 334 Scientific Party
Author Affiliation(s): Primary:
University of Firenze, Dipartamento Scienze della Terra, Florence, Italy
Other:
University of Tsukuba, Tsukuba, Japan
Volume Title: AGU 2011 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2011; American Geophysical Union 2011 fall meeting, San Francisco, CA, Dec. 5-9, 2011. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: IODP Expedition 334 took place in Spring 2011 offshore the Osa Peninsula in the Costa Rica subduction zone. This drilling expedition represented the beginning of the Costa Rica Seismogenesis Experiment (CRISP), a multi-year project aiming at exploring the processes responsible of earthquake nucleation and rupture propagation along erosive plate boundaries. During IODP Exp. 334 we obtained a comprehensive suite of data at the three upper and middle slope sites which were focused on the up-dip transition from seismic to aseismic plate boundary fault behavior, using logging while drilling (LWD) techniques and coring to depths of 450 to 950 m. A site was also devoted to drilling and coring the incoming Cocos Ridge. One highlight of LWD and core results is evidence for the orientation of present-day principal stresses from borehole breakouts, and paleostresses from fractures and faults in cores. The orientation of the maximum horizontal stress axis (SHmax) from breakouts changes from NNW-SSE in the middle slope to ENE-WSW in the upper slope site, consistent with a compressional to transpressional stress state in the outer wedge according to Cocos Ridge indentation, and an extensional state of stress in the inner wedge. Coring in the upper slope reached the forearc basement as defined by geophysical techniques. Biostratigraphy marked the oldest silty/clayey slope sediments, drilled at ≈ 900 mbsf, as being deposited at the Plio/Pleistocene boundary (≈2.2 Ma), which indicates very high sedimentation rates up to 1035 m/my. Onland uplift triggered by Cocos Ridge subduction can easily provide this material, while the processes leading to such strong forearc subsidence can be associated with subduction erosion and upper plate thinning. Both of these processes can be also linked to the landward dipping fractures/normal faults visible in seismic images, which are also characterized by localized fluid flow as revealed by shipboard geochemical data. Further results include: a) new constraints on timing and evolution of subsidence, b) continuous structural and physical property logs to better constrain the stress and strain history of forearc material, c) new heat flow measurements and d) first ever sampling of Cocos Ridge basalts.
Year of Publication: 2011
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; 16 Structural Geology; Basalts; Central America; Cocos Ridge; Cores; Costa Rica; Costa Rica Seismogenesis Project; Earthquakes; East Pacific; Expedition 334; Faults; Fractures; Heat flow; Igneous rocks; Integrated Ocean Drilling Program; North Pacific; Northeast Pacific; Ocean floors; Offshore; Osa Peninsula; Pacific Ocean; Plate tectonics; Propagation; Rupture; Sedimentation; Sedimentation rates; Seismicity; Seismotectonics; Stress; Subduction; Subduction zones; Tectonics; Uplifts; Volcanic rocks
Coordinates: N082400 N084200 W0840000 W0841100
Record ID: 2015077173
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