The recent M5.3 earthquake in Colorado and M5.9 earthquake in Virginia serve as reminders that shallow earthquakes can happen away from known fault lines. The Cascadia Region has experienced many shallow historical earthquakes. A shallow earthquake on the Seattle or Portland Hills faults would result in widespread damage and disruption. For more information on shallow earthquake, refer to CREW Cascadia Shallow Earthquakes and our other scenario documents at: EQ Scenarios.
Many recent earthquakes that grabbed headlines occurred outside of Cascadia, in countries such as Japan (Tohoku, 2011), Chile and Haiti (2010) and Indonesia (Sumatra, 2004). These far-away events, while not a part of Cascadia’s history, can teach us what to expect from future earthquakes in our region and help us plan and prepare for them.
A catastrophic magnitude 9 earthquake hit the northeast coast of Japan on March 11, 2011. The quake and resulting tsunami killed more than 15,700 people and injured another 5,300. More than 4,600 went missing. The events destroyed or damaged buildings, roads, bridges and several reactors at a nuclear power plant. Electricity, gas and water supplies, telecommunications and railway service were disrupted. Economic losses were estimated at $309 billion.
What it means for Cascadia
The tsunami generated by the Tohoku quake hit Hawaii and the U.S. west coast but caused relatively minor damage that generally was limited to beach front and harbor facilities.
- The Tohoku quake was on a subduction zone fault, almost identical to the Cascadia subduction zone fault that lies off the coast from northern California to British Columbia. The Cascadia fault last ruptured in 1700, and is capable of unleashing a tsunami every bit as powerful and devastating.
- As devastating as Tohoku was, Japanese building codes (more restrictive and expensive than U.S. codes) prevented greater destruction.
- The tsunami generated by the Tohoku quake, not the quake itself, was responsible for most of the deaths, injuries and property damage. The size of the waves (up to 33 feet or 10 meters) overwhelmed seawalls and other defenses. The only way to protect people in the tsunami’s path is to train them to evacuate to high ground when a warning is given. In the case of Tohoku, as in a potential Cascadia subduction zone tsunami, the warning is the earthquake itself.
More Tohoku resources
- Tohoku earthquake summary (U.S. Geological Survey)
- Tohoku Japan Earthquake and Tsunami Clearinghouse (Earthquake Engineering Research Institute)
- CREW forum on Tohoku’s lessons for Cascadia on the CREW YouTube channel
- Newsletter: The 2011 Japan earthquake and tsunami: Lessons for the Oregon Coast (Oregon Department of Geology and Minerals)
- The Structural Engineers Association of Washington sent a team of engineers to Japan to observe and evaluate earthquake and tsunami damage in the affected areas.
- Report: The Earthquake Engineering Research Institute sent a team to Japan to examine the societal impact of Tohoku, from casualties to economic impact. Jay Wilson of the Clackamas County (OR) Department of Emergency Management was part of this group; his video account is available on the CREW YouTube channel.