| Title | Horizontal compressive stress regime on the northern Cascadia margin inferred from borehole breakouts |
| Author | Riedel, M; Malinverno, A; Wang, K; Goldberg, D; Guerin, G |
| Source | Geochemistry, Geophysics, Geosystems (G3) vol. 17, issue 9, 2016 p. 3529-3545, https://doi.org/10.1002/2016GC006443 |
| Links | IODP Data - Données de l'IODP
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| Links | IODP Logs - Diagraphie de l'IODP
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| Year | 2016 |
| Alt Series | Earth Sciences Sector, Contribution Series 20160104 |
| Publisher | American Geophysical Union |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Province | Western offshore region; British Columbia |
| NTS | 92D |
| Area | Vancouver Island; Cascadia Continental Slope |
| Lat/Long WENS | -127.1667 -126.6667 48.8333 48.5833 |
| Subjects | marine 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; accretionary prism; gas hydrates; trend analyses |
| Illustrations | location maps; geophysical images; seismic profiles; schematic representations; geophysical logs; profiles; rose diagrams; tables |
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| Program | Western Canada Geohazards Project, Public Safety Geoscience |
| Program | Integrated Ocean Drilling Program |
| Abstract | During 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. |
| GEOSCAN ID | 299006 |
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