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The Juan de Fuca Plate is a tectonic plate generated from the Juan de Fuca Ridge and is subducting under the northerly portion of the western side of the North American Plate at the Cascadia subduction zone. It is named after the explorer of the same name. One of the smallest of Earth's tectonic plates, the Juan de Fuca Plate is a remnant part of the once-vast Farallon Plate, which is now largely subducted underneath the North American Plate.
The last megathrust earthquake at the Cascadia subduction zone was the 1700 Cascadia earthquake, estimated to have a moment magnitude of 8.7 to 9.2. Based on carbon dating of local tsunami deposits, it occurred around 1700. As reported in National Geographic on 8 December 2003, Japanese records indicate the quake caused a tsunami in Japan, which occurred on 26 January 1700.
In 2008, small earthquakes were observed within the plate. The unusual quakes were described as "more than 600 quakes over the past 10 days in a basin 150 miles southwest of Newport". The quakes were unlike most quakes in that they did not follow the pattern of a large quake, followed by smaller aftershocks; rather, they were simply a continual deluge of small quakes. Furthermore, they did not occur on the tectonic plate boundary, but rather in the middle of the plate. The subterranean quakes were heard on hydrophones, and scientists described the sounds as similar to thunder, and unlike anything heard previously.
originally posted by: watchitburn
a reply to: OneGoal
What makes us believe that it is "long overdue"? 300 years is not a geologically significant period of time.
Whats the average periodicity between major events?
And how does a few rumbles almost 10 and 15 years ago make it "built up" for a major megathrust quake?
I'm not saying it isn't, I'm no geologist. But it's information that should be included in the OP.
Scientists believe the most recent subduction zone earthquake, a M9 event, occurred in January 1700. The best available evidence indicates that these earthquakes occur, on average, every 500 to 600 years. However, the years between these events have been as few as 100 to 300 years -- meaning, all Cascadia residents should prepare to experience a powerful and potentially damaging subduction zone earthquake in their lifetimes.
Plans for managing tsunami risk on the West Coast are still evolving, according scientists speaking at the Seismological Society of America's (SSA) 2016 Annual Meeting, held April 20-22 in Reno, Nevada. k