Juan de Fuca Ridge

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The Juan de Fuca Ridge is a tectonic spreading centre with a moderate spreading rate of 6 cm/year. It has a northeast orientation and runs along the coast of Oregon, Washington and British Columbia, stretching a total distance of 500 Km. The Juan de Fuca Plate sub-ducts under the North America Plate with a slab dip ranging from 45o-65o at half the full spreading rate of 63.6 ±3.6 mm/a at S67.2oE ±7.9o relative to the Pacific Plate. To the west of the Juan de Fuca ridge sediment accumulation on the Pacific plate is much less significant compared to sedimentation rates on the Juan de Fuca plate. Sediment accumulation of the Juan de Fuca plate may be up to several kilometers thick at the Cascadia deformation front. Early seismic work done by Raitt in 1963 showed a subdivision of the crust into two main seismic layers 2A/2B; this was later expanded to recognize a 3rd layer . These boundaries have been defined by highly porous basaltic lavas, and low-porosity diabase dykes displays p-wave velocities ranging from <2.5 km/s at the ridge axis to >4km/s over mature sections of the ocean crust. The average thickness displayed by layer 2A ranged from 320±80 - 460±80 m. 2B P-wave velocity averages are higher at 5.2 km/s with velocity lows at the ridge axis (4.4±0.3 km/s) and the overall average velocity of mature ocean crust being about 5.2±0.3 km/s. The strongest impact of the velocity difference is thought to be attributed to mineral precipitation around active hydrothermal circulation centres driven by the heat from active hot magma chambers. Within the Cascadia range their are two common classification of earthquakes. The most common is the shallow North American plate earthquake. These earthquakes typically occur at depths of 0 - 30 Km. The second type of earthquakes are the much deeper earthquakes that occur within the Juan de Fuca plate between 30 and 80 Km of
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