This page shows the same data explained on the Likelihood of an 8.0 page; however, here, we explore how that data looks in Sunburst Charts rather than Bar Charts.
How to Read the Sunburst Charts shown below:
- Each number inside a slice corresponds to the “Event Number” shown on the table here.
- The width of each slice represents how long an interval was.
- The wider the slice, the more years passed between two adjacent megathrust earthquakes. For example, slice 41 stretched 577 years and is the widest slice shown.
The Pacific Northwest’s current number of years without a Cascadia megathrust earthquake (324 years) falls at the line between slice 34 (318 years) & slice 21 (330 years).
There are certainly more slimmer slices at that division than there are thicker ones. 80% of the time, the fault has not had to wait 324 years for the strain to break it.
Here, the Pacific Northwest’s current number of years without a Cascadia megathrust earthquake (324 years) is a slice that would fit between slice 24 (292 years) & slice 21 (330 years).
During the most recent 6,000 years, only two slices (intervals) have been thicker than our current amount of time without an event. To reach the “thickness” of #21, the PNW only has to make it 6 more years. The region only needs to hold off another 20 years to match the thickness of #27.
That means if the PNW makes it 21 years without an event, the region will be in the longest interval to have occurred in over 6,000 years.
Put another way, (and assuming the estimated ages from the USGS publication are accurate) during the past ≈6,000 years…93% of the time the fault has not had to wait 324 years for the strain to break it.
The Pacific Northwest hasn’t had an interval longer than
344 years in over 6 millennia.
Citation: Goldfinger, C., Nelson, C.H., Morey, A.E., Johnson, J.E., Patton, J.R., Karabanov, E., Gutiérrez-Pastor, J., Eriksson, A.T., Gràcia, E., Dunhill, G., Enkin, R.J., Dallimore, A., and Vallier, T., 2012, Turbidite event history—Methods and implications for Holocene paleoseismicity of the Cascadia subduction zone: U.S. Geological Survey Professional Paper 1661–F, 170 p. (Available at https://pubs.usgs.gov/pp/pp1661f/).
Surviving Cascadia 