This article is available on www.survivingcascadia.com, published by Bridget Good. Please note that the contents of this article are not owned by us and are being shared for educational purposes only. We have obtained permission to share this article from Bridget Good, and it is important to mention that Sound Seismic is not affiliated with Surviving Cascadia.

We prepare — or choose not to — based on our perceived risk.
For that reason alone, understanding the risk is key to 
Surviving Cascadia.

We often hear there is a “37% chance of a major Cascadia Subduction Zone (CSZ) earthquake in the next 50 years”. The probability is derived from a log-normal distribution, like that shown on the left of this image.

To see supporting details and play with the 37% probability calculations, visit Step 2 on Surviving Cascadia’s Timing The Next Big One page.

This page, however, exists because the Log-Normal formula is not the only way to evaluate the risk. In 2010, Oregon State University professor Chris Goldfinger said the following:

“Perhaps more striking than the probability numbers is that we can now say that we have already gone longer without an earthquake than 75 percent of the known times between earthquakes in the last 10,000 years,” Goldfinger said. “And 50 years from now, that number will rise to 85 percent.”

Page 2 (14/184) of the 2012 USGS research paper Turbidite Event History—Methods and Implications for Holocene Paleoseismicity of the Cascadia Subduction Zone writes:

“Failure analysis suggests that by the year 2060, Cascadia will have exceeded… 85 percent of recurrence intervals for the southern margin.”

If you have questions about what is meant by the “southern margin”, details are located on Surviving Cascadia’s Size of The Next Big One.

To fully grasp what this failure analysis means, it helps to have a visual. Take a look at this ten thousand-year historical bar graph for Cascadia. 

The horizontal blue line in the graph above lies at 360 years — the amount of time that will have passed between the last major CSZ quake in 1700 and the year 2060 (the year mentioned in the USGS paper) if an earthquake doesn’t occur by then. Intervals longer than 360 years are shown in red, while those that are shorter are in green.

Only 6 intervals stretch above the blue line… and they’re kind of clumped together. More on that in a minute.

Read the full article here: https://survivingcascadia.com/37-in-50-years/