Earthquakes and Tsunamis on the Oregon Coast

Patrick Corcoran, Hazards Outreach Specialist, Sea Grant Extension, OSU

Seaside, OR Japan 2011

The Bottom Line►Giant Earthquakes Happen Here!

►They Occur Regularly in Geologic Time

►Our Last one Was in 1700 (313 years ago)

►Given 10k year Averages, We’re About Due

►EXPECT IT!

Seriously, this is the shift that matters…

EXPECT IT!

It will change the way you live

The 3 Things You Need to Know

►Big earthquakes make big tsunamis. Know the difference between Local and Distant events.

►If you feel the earth quake, Get to high ground fast (15-30 min). Locate now the Danger Zones and Safe Zones where you live, work, and play.

►Instruct Loved Ones to get to high ground, stay there overnight, and find each other at a shelter. ID non-local contact person to call.

Source: Patrick Corcoran, Sea Grant Extension, Oregon State University

2 Scenarios Exercise

►Distant Event: What did you do on 3.11? What would you do differently?

►LOCAL EVENT!

►Ranging from an M8 quake at either end of fault, with moderate shaking locally, limited, localized tsunami damage. To a Full Rip 9 M9 quake underfoot. Major destruction, liquifaction, subsidence, landslides, large tsunamis and inundation.

3 Types of PNW Earthquakes

►Crustal: near the surface of a plate

► Interplate: between two plates adjacent plates

►Subduction: overlapping plates, mega thrust

PNW Earthquakes & Tsunamis:Local event scenarios

1. Cascadia Subduction Zone earthquakes: 1700

2. Deep intraplate earthquakes: 1949, 1965, 2001

3. Shallow earthquakes: 900, 1872, 1992, 1993

3 Types of PNW Tsunamis

►GOOD: Distant events from anywhere outside the region (AK, JP, CH, etc.)

►BAD: Partial CSZ rupture (So. or N.) damage will be worse near epicenter and less so farther away

►UGLY: Full CSZ. Widespread regional disaster. Major quake, major tsunamis

10,000 year average* recurrence:

The entire length erupts M9 every 500 years

The southern portion erupts M8 every 250 years

The last event was event was 313 years ago…

19 M9‘s in past 10,000 years !

What is known

The PNW, at 313 years into the cycle of recurrence, is far enough into it that

a prudent society would be better prepared

(75% have happened by now)

Astoria

Young’s Bay

Evidence of the last four Cascadia events, estimated top to bottom as AD:

17001400900400

Local Earthquake► If you FEEL a large earthquake: immediately duck

down, cover your head from falling debris, and hold on until the shaking stops.

► Stay put unless your building is damaged and dangerous, then moved to open ground.

► Avoid power lines, gas leaks, and fires. Administer first aid and help others find shelter.

► Execute your family plan. (What did you say you

were going to do? Do you have the discipline to do it?)

► Expect aftershocks and related trauma and damage.

M 9.0 Earthquake and Landslides…

Source: Oregon Dept Geology and Mineral Industries

Amplification of Soil and Fill

Source: Oregon Dept of Geology and Mineral Industries

Big Earthquakes Cause Big Tsunamis!

A large earthquake IS your warning that tsunamis are on

their way in 15 – 30 minutes!!

Local Tsunamis► The areas vulnerable to surge and flooding by

tsunamis include all beaches, shorelines, coastal waterways, and wetlands. Much development exists in these areas.

► Locate where you live, work, and play on these maps and “know where to go” to avoid tsunamis when the next Big One occurs. There will be no warning, you will have 15 – 30 minutes to get to high ground. Period.

► Maps portray the WORST case scenario for a LOCAL event. (Distant events create smaller tsunamis) Get maps at city halls, fire stations, etc.Source: Patrick Corcoran, Sea Grant Extension, Oregon State

University

New Maps !

►Evacuation Brochures: Worst case local worst case distant*

►Tsunami inundation maps (TIM): Show range of the inundations of the past 19 events. More nuanced. For planning purposes

19 M9‘s in past 10,000 years !

How Do I Reconnect With Family?

DISTANT No problem. Phones, roads and infrastructure may be busy, but intact. Drive home or stay overnight with “friends in high places.”

► LOCAL Big problem. Instruct loved ones to get to high ground, stay there overnight, and find each other later at a shelter. ID a non-local contact person for everyone to call. Do not rush to meet at a designated place as that will likely require family to re-enter danger zones.

► Power and all phones will be out. Roads and bridges will be destroyed. You will likely not be in communication for a while. Insist that everyone knows what to do to be safe wherever they are. Don’t re-enter inundation zones for 12 hours. Talk through these scenarios. Source: Patrick Corcoran, Sea Grant Extension, Oregon State

University

Families and

Loved Ones

►Do your loved ones understand this infrequent but real hazard? Do they Expect it?

►Will they take distant events in stride; but when the earth quakes move to high ground, stay there overnight, and find you the next day? Are you sure?

Neighbors and the Hood

►Earthquakes: Structural design, egress out, etc.

►Tsunamis: Location, and connectivity after

►Training for residents, businesses

Map Your Neighborhood!

►Connected communities are more resilient

►We have lots of resources! Everyone has a contribution.

►Be prepared enough to help others!

Overwhelming Opportunities

► Political leadership and government support

► Businesses and Chambers of Commerce

► Schools, hospitals and public heath

► Public works, ODOT, planning departments

► Individuals, families, and neighborhoods, CERTS!!

We’re Culturally Unprepared

► Research has only in the past 25+ years revealed that Cascadia erupts in Great (M9) earthquakes and tsunamis.

► It’s understandable that we’re behind the curve. But, we must make up for lost time. We must prepare commensurate with the risk—which is great.

► In Japan 2011, 20k people tragically died. But over 200k were in the inundation zone at the time. So, 90% of Japanese successfully evacuated!