Cascadia and San Andreas Fault are linked. What is Their Frequency of Major Earthquakes? 2022-12-14. Jorma Jyrkkanen

According to USA Earthquake Geologists, Looking at Sediments going Back 10,000 Years.

Location of core sample sites. U.S. Geological Survey scientists studied undersea core samples of soil looking for turbidites -- deposits of sediments that flow along the ocean floor during large earthquakes. The samples were gathered from more than 50 sites during cruises in 1999, 2002 and 2009.

Overall the stated frequency going back 10,000 years is every 246 years. The last one was in 1700. That was 323 years ago and that is 76 years longer than the average frequency. However if you examine the chart closely, you will note that about 5000 years ago the frequency increased and the interval between quakes was shortened. I compute it as [(5000-323)/25]= 187 yrs mean frequency during this interval. In other words by this reasoning, the next one should have happened in 1887. Perhaps this was the Big One in San Fransisco in 1906, only 19 years later than the new computed frequency.

It appears that its companion Cascadia megathrust has another one up its sleeve from the pairing we are seeing on the frequency chart that is overdue now and we are well within the time interval for it to happen. Please be prepared and have a plan.