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TitleHorizontal compressive stress regime on the northern Cascadia margin inferred from borehole breakouts
AuthorRiedel, M; Malinverno, A; Wang, KORCID logo; Goldberg, D; Guerin, G
SourceGeochemistry, Geophysics, Geosystems (G3) vol. 17, issue 9, 2016 p. 3529-3545, Open Access logo Open Access
LinksIODP Data - Données de l'IODP
LinksIODP Logs - Diagraphie de l'IODP
Alt SeriesEarth Sciences Sector, Contribution Series 20160104
Mediapaper; on-line; digital
File formatpdf
ProvinceWestern offshore region; British Columbia
AreaVancouver Island; Cascadia Continental Slope
Lat/Long WENS-127.1667 -126.6667 48.8333 48.5833
Subjectsmarine geology; tectonics; geophysics; structural geology; sedimentology; continental margins; continental slope; subduction zones; stress analyses; geophysical logging; boreholes; resistivity logging; geophysical surveys; seismic surveys, marine; deformation; structural analyses; structural features; faults; folds; submarine ridges; slope failures; bathymetry; Cascadia Continental Margin; Cascadia Subduction Zone; Juan de Fuca Plate; North American Plate; gas hydrates
Illustrationslocation maps; geophysical images; seismic profiles; schematic representations; geophysical logs; profiles; rose diagrams; tables
ProgramPublic Safety Geoscience Western Canada Geohazards Project
ProgramIntegrated Ocean Drilling Program
Released2016 09 04
AbstractDuring Integrated Ocean Drilling Program Expedition 311 five boreholes were drilled across the accretionary prism of the northern Cascadia subduction zone. Logging-while-drilling borehole images are utilized to determine breakout orientations to define maximum horizontal compressive stress orientations. Additionally, wireline logging data at two of these sites and from Site 889 of Ocean Drilling Program Leg 146 are used to define breakouts from differences in the aperture of caliper arms. At most sites, the maximum horizontal compressive stress SHmax is margin-normal, consistent with plate convergence. Deviations from this trend reflect local structural perturbations. Our results do not constrain stress magnitudes. If the margin-normal compressional stress is greater than the vertical stress, the margin-normal SHmax direction we observe may reflect current locking of a velocity-weakening shallow megathrust and thus potential for trench-breaching, tsunamigenic rupture in a future megathrust earthquake.
Summary(Plain Language Summary, not published)
Crustal stresses control the occurrence of earthquakes. One of the most direct means of measuring crustal stresses is the analysis of borehole breakouts which refers to the failure of portions of the wall of a borehole in the direction of the least compressive stress. Breakouts in several boreholes drilled in the accretionary prism of the northern Cascadia subduction zone, off Vancouver Island, are analysed in this work. The results indicate margin-normal compression of the prism in the present interseismic state of the Cascadia great earthquake cycle and are consistent with the locking of the megathrust.

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