When the Juan de Fuca tectonic plate goes beneath the North American plate, it begins to get crushed.  The heat from the friction of the two massive plates rubbing together, melts the Juan de Fuca plate into Magma (lava).

Goldfinger et al. (2012) interpreted a 10,000-year old sequence of deep sea turbidites at the Cascadia subduction zone (CSZ) as a record of clusters of plate-boundary great earthquakes separated by gaps of many hundreds of years. We performed statistical analyses on this inferred earthquake record to test the temporal clustering model and calculate time-dependent recurrence intervals and probabilities. We used a Monte Carlo simulation to determine if the turbidite recurrence intervals follow an exponential distribution consistent with a Poisson (memoryless) process. The latter was rejected at a statistical significance level of 0.05. We performed a “cluster analysis” on 20 randomly simulated catalogs of 18 events (event T2 excluded), using ages with uncertainties from the turbidite dataset. Results indicate 13 catalogs exhibit statistically significant clustering behavior, yielding a probability of clustering of 13/20 or 0.65. Most (70%) of the 20 catalogs contain 2 or 3 closed clusters (a sequence that contains the same or nearly the same number of events) and the current cluster T1 to T5 appears consistently in all catalogs. Analysis of the 13 catalogs that manifest clustering indicates that the probability that at least one more event will occur in the current cluster is 0.82. Given that the current cluster may not be closed yet, the probabilities of a M 9 earthquake during the next 50 and 100 years were estimated to be 0.17 and 0.25, respectively. We also analyzed the sensitivity of results to including event T2, whose status as a full-length rupture event is in doubt. The inclusion of T2 did not change the probability of clustering behavior in the CSZ turbidite data, but did significantly reduce the probability that the current cluster would extend to one more event. Based on the statistical analysis, time-independent and time-dependent recurrence intervals were calculated.  https://www.researchgate.net/profile/Chris_Goldfinger

CT scan, photograph, mean grain size, magnetic susceptibility and composition information showing the structure of a stratigraphic unit from approximately 1500 cal yr BP in the new Sanger Lake core (SL2010). Results suggest two fining upward sequences, with fine silt and clay caps (which take time to settle from the water column). The presence of high concentrations of woody debris alters the magnetic susceptibility and density records of this sequence. (b) Based on similarities in physical properties and event timing, this event is thought to correlate to marine event T5. Both data sets support the idea that T5 may be a composite of two events closely spaced in time, which is supported by the presence of two deposits from the same time at Bradley Lake, which were determined to be ∼ 20-40 yr apart based on the evaluation of varves separating the two events (Goldfinger et al., 2012).

IF THE GROUND IS MOVING FOR OVER 4 MINUTES, ITS PROBABLY A SUBDUCTION ZONE EARTHQUAKE!

The Cascadia lies underwater where the oceanic plate actually dives under the North American Plate.


The "Cascadia subduction zone" derives its name from the Cascade Range of volcanic mountains that parallel the fault from afar and from how one plate subducts, or goes under, another.  This page is simply to gather information to share, so you can prepare.  

Northwest Earthquakes

Preliminary correlations between Cascadia Channel core M9907-23PC and core MD02-2494 from Effingham Inlet, western Vancouver Island, Canada. Each plot shows the magnetic-susceptibility record (blue) from an Effingham Inlet (inner basin) turbidite, and a magnetic-susceptibility or gamma-density record from our 1999 cores in Cascadia Channel (in purple). These events were interpreted as seismites by Dallimore et al. (2005), Thomson and others (2005) based on the wall-rock signature from the adjacent fiord walls (shown in grey) and by comparison to the historical turbidite triggered by the1946 Vancouver Island earthquake. The records show a striking similarity in general size, number of sandy pulses (magnetic and density peaks) and in some cases, detailed trends. Radiocarbon ages also are first-order compatible, but have separations of 100-200 yr in some cases. The combined age data and stratigraphic correlation suggest that the Effingham turbidites and Cascadia Basin turbidite signatures are recording the same earthquakes. Effingham data from Dallimore et al. (2009).

OREGON & WASHINGTON EARTHQUAKES AND TSUNAMIS

CASCADIA SUBDUCTION ZONE

PACIFIC NORTHWEST . San Andreas Fault

Fig. 5. Preliminary correlations between Cascadia Channel core M9907-23PC and core MD02-2494 from Effingham Inlet, western Vancouver Island, Canada. Each plot shows the magnetic-susceptibility record (blue) from an Effingham Inlet (inner basin) turbidite, and a magnetic-susceptibility or gamma-density record from our 1999 cores in Cascadia Channel (in purple). These events were interpreted as seismites by Dallimore et al. (2005), Thomson and others (2005) based on the wall-rock signature from the adjacent fiord walls (shown in grey) and by comparison to the historical turbidite triggered by the1946 Vancouver Island earthquake. The records show a striking similarity in general size, number of sandy pulses (magnetic and density peaks) and in some cases, detailed trends. Radiocarbon ages also are first-order compatible, but have separations of 100-200 yr in some cases. The combined age data and stratigraphic correlation suggest that the Effingham turbidites and Cascadia Basin turbidite signatures are recording the same earthquakes. Effingham data from Dallimore et al. (2009).

There are around 500,000 earthquakes each year. 100,000 of these can actually be felt. The largest earthquake ever recorded was a magnitude 9.5 (Mw) in Chile on May 22, 1960. The world's deadliest recorded earthquake occurred in 1556 in central China.

(a) CT scan, photograph, mean grain size, magnetic susceptibility and composition information showing the structure of a stratigraphic unit from approximately 1500 cal yr BP in the new Sanger Lake core (SL2010). Results suggest two fining upward sequences, with fine silt and clay caps (which take time to settle from the water column). The presence of high concentrations of woody debris alters the magnetic susceptibility and density records of this sequence. (b) Based on similarities in physical properties and event timing, this event is thought to correlate to marine event T5. Both data sets support the idea that T5 may be a composite of two events closely spaced in time, which is supported by the presence of two deposits from the same time at Bradley Lake, which were determined to be ∼ 20-40 yr apart based on the evaluation of varves separating the two events (Goldfinger et al., 2012).

EARTHQUAKE WATCH FOR THE NEXT 7 DAYS FOR CALIFORNIA, NORTHWEST ARIZONA, OREGON, WASHINGTON


The Cascadia subduction zone (also referred to as the Cascadia fault) is a convergent plate boundary that stretches from northern Vancouver Island to northern California. It is a very long, sloping subduction zone that separates the Explorer, Juan de Fuca, and Gorda plates, on the one hand, and the North American Plate, on the other.

The denser oceanic plate is subducting beneath the less dense continental plate offshore of British Columbia, Washington, Oregon, and northern California. The North American Plate moves in a general southwest direction, overriding the oceanic plate. The Cascadia subduction zone is where the two plates meet.

Tectonic processes active in the Cascadia subduction zone region include accretion, subduction, deep earthquakes, and active volcanism of the Cascades. This volcanism has included such notable eruptions as Mount Mazama (Crater Lake) about 7,500 years ago, Mount Meager about 2,350 years ago, and Mount St. Helens in 1980.[1] Major cities affected by a disturbance in this subduction zone would include Vancouver and Victoria, British Columbia; Seattle, Washington; and Portland, Oregon.  From Wikipedia


                   
EARTHQUAKES IN THE NORTHWEST - WEST COAST WATCH AND OTHER NEWS ON QUAKES...

               SAN ANDREAS MAP AND NORTH AMERICAN PLATE   *  JUAN DE FUCA & SUBDUCTION ZONE