Oregon geology: 'The next ‘Big One’ is imminent'

Oregon geology: 'The next ‘Big One’ is imminent'
Patrick Corcoran's job is to educate Oregonians about how to stay safe when the next "Big One" earthquake and tsunami reach our shores. He is a hazards outreach specialist with the OSU Extension Sea Grant program and lives in Astoria.

Courtesy OSU News & Communications

Two weeks after tsunamis in Sumatra and American Samoa initiated by powerful earthquakes killed hundreds of people, a growing number of Oregonians are wondering how people living along the West Coast will fare when a large – and possibly overdue – quake shakes our own soil.

"Unfortunately, our fascination with the physical phenomena eclipses our interest in preparing to survive our next big earthquake and tsunami," said Patrick Corcoran, a hazards outreach specialist with the Oregon Sea Grant program at Oregon State University.

The Cascadia Subduction Zone, which stretches more than 700 miles from northern California to Vancouver Island in British Columbia, has experienced several major earthquakes during its long history.

"The release of pressure between two overlapping tectonic plates along the subduction zone regularly generates massive 9.0 magnitude earthquakes – including five over the last 1,400 years," Corcoran said. "The last 'Big One' was 309 years ago. We are in a geologic time when we can expect another ‘Big One,’ either in our lives or those of our children.

"Prudence dictates that we overcome our human tendencies to ignore this inevitability," he added.

Corcoran teaches people who live in or visit Oregon coastal areas three key things they need to know about tsunamis.

The first, he says, is to know the difference between local and distant earthquakes. A local earthquake feels powerful and lasts up to five minutes. Duck, cover your head and hold on until the shaking stops, he advises, and then run for higher ground. You'll have 15 to 30 minutes to get to a height of 50 to 100 feet above sea level to be safe.

"The tsunami is a series of surges, and often the first one is not the biggest," Corcoran warned. "Wait 12 hours to return to the area and do not expect to be able to drive or use telephones or cell phones."

If you hear an official warning but do not feel an earthquake, you have more time: an earthquake happened somewhere else and you should have a few hours to evacuate the beach, lowlands and waterways. Turn on local television and radio stations to find more information and wait 12 hours to return to the beach or lowlands.

A second key piece of information is to know the location of local earthquake and tsunami “danger zones,” which Corcoran says can be surprisingly large. They are defined on official maps from the Oregon Department of Geology and Mineral Industries
 
Evacuation zones for the Oregon coast also can be found online.

Use the maps to identify not only the dangerous areas where you live, but also where you work, shop and play, Corcoran advised, and note what routes will take you to safety. Maps also are available at fire departments and city halls.

"For distant tsunamis, as a general guideline, consider the inundation to be similar to a severe winter storm at high tide," Corcoran said. Distant tsunamis are more frequent but much less dangerous. Most people won't need to go anywhere; and staying put will greatly help local officials.

A third key piece of preparedness is planning how to reconnect with loved ones. Have a family plan for what to do if separated in a disaster. For a local event, Corcoran suggests teaching everyone to get to safety, stay there and reconnect when it's over. Messages for children might include, "Don't try to return home between waves. We'll find each other when it is safe."

Identify a non-local person in another state for everyone to call as soon as possible. You may have to try alternative communication tactics to landlines – and even cell phones – such as texting, satellite phones or HAM radio. If the tsunami is from a distant earthquake, phone lines will be undamaged, but likely overloaded.

Among other safety tips:

  • Sirens do not mean run. Ironically, sirens indicate a distant tsunami and three or more hours to evacuate the inundation zone;
  • Don't plan on driving your vehicle to safety after a major earthquake. Damage to your garage door, a tree across the driveway, a power line across the road, broken bridges and landslides likely will make driving to safety impossible – and a waste of precious time;
  • In addition to buying an emergency kit, which could get covered with rubble, take CPR and first aid classes;
  • Consider buying a NOAA all-hazards radio, which will give immediate information on where a distant earthquake is located and how soon a tsunami might arrive.

"The next ‘Big One’ is imminent," Corcoran said, "but education can vastly improve our odds of surviving the earthquake and tsunami. Education also can save us from unnecessary chaos from distant, smaller events."