Present-day principal horizontal stress orientations in the Costa Rica subduction zone; preliminary estimates from logging-while-drilling, IODP Expedition 334

Author(s): Saito, S.; Malinverno, A.; Yamamoto, Y.; Lin, W.; Kitamura, Y.; Hashimoto, Y.; Wu, H.; Ujiie, K.; Vannucchi, P.; Stroncik, N.
Integrated Ocean Drilling Program, Expedition 334 Scientists
Author Affiliation(s): Primary:
Japan Agency for Marine-Earth Science and Technology, IFREE, Yokosuka, Japan
Lamont-Doherty Earth Observatory, Palisades, NY, United States
University of Tsukuba, Tsukuba, Japan
University of Florence, Florence, Italy
Texas A&M University, College Station, TX, United States
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: Integrated Ocean Drilling Program (IODP) Expedition 334 is the first step in the Costa Rica Seismogenesis Project (CRISP), designed to understand the processes that control nucleation and seismic rupture of large earthquakes at erosional subduction zones. The scientific objectives of this expedition include constraining the architecture and evolution of the plate boundary megathrust, the role of fluids, as well as the nature of the upper plate in a tectonically erosive margin along a drilling transect at two slope sites. One of our goals was to obtain a comprehensive suite of geophysical logs at two sites using logging-while-drilling (LWD) technology. The principal objectives of the LWD program were to document in situ physical properties (natural gamma ray, density, neutron porosity, resistivity), stratigraphic and structural features, compaction state, and hydrological parameters. Density and borehole radius images were used to determine stress orientations from borehole breakouts. Despite their limited azimuthal resolution, the borehole images clearly display vertical bands of large borehole radius in the interval 110-438 mbsf at Hole U1378A and in the interval 292-885 mbsf at Hole U1379A, interpreted as borehole breakouts caused by differences in the principal horizontal stresses. The average azimuth of the breakouts at Site U1379 is roughly NE-SW to ENE-WSW, indicating that the maximum horizontal stress is oriented NW-SE to NNW-SSE. The average azimuth of the breakouts at Site U1378 is roughly N-S to NNW-SSE, indicating that the maximum horizontal stress is oriented E-W to ENE-WSW. The borehole breakouts also yield useful information on stress magnitudes. The principle is that the width of the breakout is dependent on the stress magnitudes and the compressive strength of the borehole wall rock. In order to constrain the range of possible stress magnitudes, we will report on preliminary results of rock compressive strength analyses, as well as the width of borehole breakouts.
Year of Publication: 2011
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 16 Structural Geology; Borehole breakouts; Boreholes; Compressive strength; Costa Rica Seismogenesis Project; Earthquakes; East Pacific; Expedition 334; IODP Site U1378; IODP Site U1379; Integrated Ocean Drilling Program; North Pacific; Northeast Pacific; Orientation; Pacific Ocean; Physical properties; Rupture; Seismotectonics; Stress; Subduction zones; Tectonics
Coordinates: N083532 N083532 W0840438 W0840438
N084051 N084051 W0840201 W0840202
Record ID: 2015077174
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