I grew up in Salem and I've never heard a thing about earthquakes in Salem. My wife's family came to the Willamette valley in the 1850s and no one in her family has ever heard of earthquakes in the Willamette valley. When we moved back to Salem from Seattle we thought we'd be getting away from the risk of earthquakes.
However, in the last 15 years Oregon geologists have come to understand the following facts:
- The Willamette valley has had big (magnitude 8 and 9) earthquakes (called subduction zone quakes) on the average of every 250 years for a very, very long time (many thousand years). This is recorded in the geologic record.
- The last big (magnitude 9) quake in Salem was in 1700, before white men were here. They know the exact date, time and size of this quake because the time and height of the Tsunami was recorded in Japanese historical records.
- Local Indian folklore has stories about big earthquakes and Tsunamis.
- We are currently 311 years into a 250 year earthquake cycle.
- The reason the quakes here are bigger here than Seattle and California is because of the nature of the Cascadia subduction zone along the Oregon coast.
This lecture by James Roddey of the Oregon Dept of Geology explains all the ugly details. It's an hour and 10 minutes but it's well done and well worth understanding this subject.
The bottom line is that these big magnitude 9 quakes are not likely to kill many people but they disable the infrastructure (roads, bridges, power grid, etc.) from northern CA through OR and to BC for a very long time. You need to be able to survive on your own for months!