Cascadia Subduction Zone

Cascadia Subduction Zone

According to the United States Geological Survey (USGS) the forces that produce earthquakes in western Oregon are generated as the Juan de Fuca oceanic plate moves northeastward with respect to the North American continental plate at an average rate of about 1.5 inches per year along the Pacific Northwest coast. At the zone of contact between the North America and Pacific Plates, the Juan de Fuca Plate slides beneath the North American continent and sinks slowly into the earth’s mantle, producing the Cascade volcanoes and earthquakes. The zone of the shallow, east-dipping subducting plate is called the Cascadia Megathrust Fault.

Cascadia Subduction Zone

Cascadia Subduction Zone – Juan de Fuca Triple Junctions and Cascade Volcanic Arc

Studies have shown through geological evidence provided by buried soil layers, dead trees, and tsunami deposits that about every 500-600 years the upper portion of the shallow dipping Cascadia Fault ruptures offshore and releases this compression and causes great earthquakes of magnitude 8 to 9. (The information provided for this section was from a very fascinating read from the USGS entitled Earthquake Hazards and Lifelines in the Interstate 5 Urban Corridor.)

The consequence of a Subduction Zone earthquake are the largest earthquakes in the world, with a result of a minimum 8.5 magnitude quake.  The last “big one” from the CSZ was in January 1700, the average times between quakes are less than 300 years apart.  Needless to say, we are overdue.

We can expect numerous situations during and after a large-scale earthquake:

  • The earthquake could last minutes, followed by equally large aftershocks and Tsunamis
  • Utilities
    • No power for at least a month
    • Full scale utility service restoration (power, gas, water, sewer, communications, etc.) could take 3 to 12 months, if not longer.
    • No clean water
    • No access to sanitation
    • Broken waterlines
    • Fires due to leaking gas lines
  • Damaged roads and bridges destroyed
  • Thousands dead
  • Tens of thousands injured
  • Tens of thousands homeless

Reading this can seem bleak, but if we prepare and educate ourselves on how to live through and survive a “megathrust” quake, our chances of survival with multiply.

We have created an earthquake preparation page with guides and checklists on how you can prepare for yourself and your family during and after a major earthquake.

Additional websites with information regarding the earthquakes in the Northwest and the Cascadia Subduction Zone:

Seismic Retrofit Common Questions

 Why should I retrofit my home? 

  • To reduce the damage to your home, lessen the potential for injury and the loss of sentimental and monetary valuables.
  • Without retrofitting your home, you will not be able to obtain earthquake insurance.  In the case of a major earthquake and your home is destroyed, without insurance, you are left with a mortgage payment and no house.
  • Most crucial is the ability to occupy your home for weeks, even if it is destroyed. To think of your home as a shelter after a disaster is vital, you could still remain in the house to stay dry and limit your exposure to the weather.

What size earthquake will this protect me against?

Retrofitting your home does not equal fortification of your structure. The main goal of retrofitting your home is to reduce your risk against major injuries, protection of material property and to give you and your family the resiliency to survive, by using your home as a shelter against the elements.

What does it mean to retrofit?

In the most basic of terms, it is the modification of an existing structure to make them more resistant to seismic activity. Retrofitting can help prevent the home from slipping off the foundation and/or collapsing.  Please see our videos below showing the difference between and unattached and an attached home and how retrofitting can protect your investment.

Unattached house video  Attached house video

What about my water heater and other utilities?

Hot water heaters should be strapped to a wall or post to protect people from a bursting water heater and reduce fire potential. The installation of natural gas shut-off valves can help prevent houses from catching fire from natural gas lines.

I have an older home, why should I be worried about my home in an earthquake?

The majority of older homes are built and sit on top of a foundation and are not attached to it. Unless your home is built on a concrete slab, it is highly likely that it is constructed on a raised foundation with a crawlspace or basement. This type of construction does not give your home the strength to hold up to a strong earthquake that produces powerful lateral and upward movements, it will literally be knocked off its foundation.

The purpose of retrofitting is to attach the home to the foundation and give it the stability that it needs to withstand a violent earthquake.

Please visit our Seismic Retrofit Attachments – Illustration and Photos page for a detailed view of completed seismic upgrades.