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TitleHydrological response to a seafloor spreading episode on the Juan de Fuca ridge
AuthorDavis, E; Becker, K; Dziak, R; Cassidy, J; Wang, K; Lilley, M
SourceNature vol. 430, no. 6997, 2004 p. 335-338,
Alt SeriesGeological Survey of Canada, Contribution Series 2004093
PublisherSpringer Nature
Mediapaper; on-line; digital
File formatpdf
ProvinceWestern offshore region
AreaJuan de Fuca Ridge
Lat/Long WENS-129.0000 -128.4167 49.0000 48.3333
Subjectsgeophysics; tectonics; marine geology; mid-ocean ridges; sea floor spreading; rift valleys; rifting; seismic zones; seismology; earthquakes; hydrothermal systems; pressure-temperature conditions; formation fluids; formation water; formation pressures; discharge rates; hydraulic head; strain; oceanic crust; igneous rocks; intrusions; dykes; boreholes; Juan de Fuca Ridge; Middle Valley rift; microbial activity; negative pressure transient; co-seismic dilatation
Illustrationsgeophysical images; focal mechanisms; plots
Released2004 07 15
AbstractSeafloor hydrothermal systems are known to respond to seismic and magmatic activity along mid-ocean ridges, often resulting in locally positive changes in hydrothermal discharge rate, temperature and microbial activity, and shifts in composition occurring at the time of earthquake swarms and axial crustal dike injections. Corresponding regional effects have also been observed. Here we present observations of a hydrological response to seafloor spreading activity, which resulted in a negative formation-fluid pressure transient during and after an earthquake swarm in the sediment-sealed igneous crust of the Middle Valley rift of the northernmost Juan de Fuca ridge. The observations were made with a borehole seal and hydrologic observatory originally established in 1991 to study the steady-state pressure and temperature conditions in this hydrothermally active area. The magnitude of the co-seismic response is consistent with the elastic strain that would be expected from the associated earthquakes, but the prolonged negative pressure transient after the swarm is surprising and suggests net co-seismic dilatation of the upper, permeable igneous crust. The rift valley was visited four weeks after the onset of the seismic activity, but no signature of increased hydrothermal activity was detected in the water column. It appears that water, not magma, filled the void left by this spreading episode.