IT’S NOT OUR FAULT!
By Deborah Maynard, Lt Col, CAP USAF and TC4 Member
Article 1 in the Great Shake Out Series sponsored by Tillamook County Citizen Corps Council - TC4
The Cascadia Subduction Zone and the three types of earthquakes it produces. Graphic: U.S. Geological Survey.
Oh yes it is! If you have not heard by now, Oregon has a fault – it’s called the Cascadia Subduction Zone and it runs from California to British Columbia between 70 to 100 miles off the coast of the Pacific Northwest. It is our fault and the more we know about what a fault is and how it affects the area around it, the better prepared we are to handle the possible outcomes.
Movement in the Cascadia Subduction Zone has not produced a big earthquake since 1700 and is building pressure where the Juan de Fuca Plate is slipping beneath the North American plate (see picture).
Our fault has the potential to produce a 9.0+ magnitude earthquake resulting in a tsunami of up to 100 feet in height. Impact to the coastal area could be dramatic. Just because the fault has the potential to generate a mega earthquake does not mean it WILL happen tomorrow, only that it could happen in the near future so it is better to be prepared than not. Be Prepared, not Scared!
How do we know significant movement has even occurred in the Cascadia Subduction Zone? Just look at the historical record. The last big earthquake which occurred due to a Cascadia Subduction fault movement was on Jan. 26, 1700. Researchers estimated the quake was 9.0 in magnitude. It caused the coastline to drop several feet initiating a tsunami that hit land with disastrous effects. This information originally came from Japan’s geological record.
A tsunami struck their coast which was directly linked to a huge earthquake in the Pacific Northwest. Native American legends also support the timing of this great event. There have been some 43 major earthquakes in the Cascadia Subduction Zone in the last ten-thousand years.
So, what does that mean for Oregon coastal areas? A potential 9.0+ magnitude earthquake could generate a tsunami up to one-hundred feet high. Shaking from this kind of megathrust quake could last up to seven minutes and extend several miles inland. As the quake tremors, or waves of earth movement, extend inland they will decrease in intensity, however, our coastal range will suffer landslides and structural destruction. Waterways may change their paths and portions of land may rise or drop several feet.
What happens when the ground shakes violently? All kinds of bad stuff! Powerlines come down. Pipes break. Things fall over and break in the worst possible places. Things get jammed up or torn apart. Pets hide, shivering in fear. Roads and bridges come apart and fall down. Buildings collapse and people are often injured and trapped!
So, what do we do? Plan, prepare and practice!
Taking the first step involves planning. Be aware of the risks and hazards wherever you and your family spend time; ie: home, school, errands, traveling, etc. Plan to participate in the GREAT SHAKE OUT exercise. October 15th is designated as the day to practice. The GREAT SHAKE OUT on 10/15 at 10:15 am is the day and time for everyone to participate in a practice exercise for a catastrophic earthquake and subsequent tsunami (for more information see: https://www.shakeout.org/oregon/ ). Schools will practice their evacuation plans; people should practice finding their community’s evacuation Safe Places (Neighborhood Gathering Points, Assembly Areas, etc.) and check in. In addition, participants can learn about their neighbors and possible needs in the event of evacuation. This exercise will provide the knowledge you need to begin planning your survival and the survival of those you love. Plan to plan!
Currently, scientists are predicting there is about a 37% chance that a megathrust earthquake of 7.1 (or more) magnitude in the Cascadia Subduction Zone will occur in the next 50 years. This event will be felt throughout the Pacific Northwest and when the earth starts shaking, you need to know what to do and where to go. Make a plan today!
Resources:
The Great ShakeOut: Tillamook County
https://www.tillamookcounty.gov/emergency-management/page/great-oregon-shakeout-10152026-1015-am
The Great Shake Out: Oregon https://www.shakeout.org/oregon/
Cascadia Subduction zone https://en.wikipedia.org/wiki/Cascadia_subduction_zone
Watching the Cascadia Subduction Zone:
5.3 Earthquake off Coast of Oregon.. Watching the Cascadia Subduction Zone. Sunday Night update.
USGS Magnitude 2.5+ Earthquakes, Past Day https://earthquake.usgs.gov/earthquakes/map/?extent=-22.59373,-189.14063&extent=72.28907,-0.87891
Oregon Dept of Emergency Management https://www.oregon.gov/oem/pages/default.aspx
Trip Check https://tripcheck.com or call 511