Earthquake Early Warning in Oregon and Washington
Events
To help residents of the Pacific Northwest learn how to use ShakeAlert, a team of organizations has been rolling out various events and resources over the next few months. Two evens have already taken place:
18 February: Pacific Northwest ShakeAlert Ask Me Anything on Reddit, in which representatives from the USGS, Oregon Office of Emergency Management, Pacific Northwest Seismic Network, University of Oregon and Washington State Emergency Management Division answered questions related to the Washington State WEA demonstration, Oregon and Washington alert delivery rollouts, and anything else that relates to ShakeAlert earthquake early warning in the Pacific Northwest.
25 February: Washington state ShakeAlert Wireless Emergency Alert (WEA) demonstration: The Washington Emergency Management Division and the USGS jointly delivered a ShakeAlert-powered WEA test message through FEMA’s Integrated Public Alerting & Warning System across wireless devices in King, Pierce and Thurston counties. This test coincided with the 20th anniversary of the 28 February 2001 Nisqually earthquake, which was Washington’s most recent damaging earthquake. WEA is one of multiple methods used by the ShakeAlert earthquake early warning system that will provide public alerting in Washington state beginning in May of this year.
“There are a lot of people who remember the Nisqually earthquake and testing our earthquake early warning system is a great way for us to get ready for the rollout of public alerting to wireless devices in May,” said Maximilian Dixon, geologic hazards supervisor for the Washington Emergency Management Division. “Testing WEA distribution of ShakeAlert-powered alerts on Feb 25th is an important step before rolling out public alerting to wireless devices in May. This is all part of a monumental effort to reduce our state’s earthquake and tsunami risk.
Two more events are scheduled for the coming weeks:
11 March: ShakeAlert-powered alert delivery to wireless devices goes live in Oregon. Leading up to 11 March, Oregon, in collaboration with USGS and other partners, will use various methods to announce the availability of alerts powered by the ShakeAlert Earthquake Early Warning system to be delivered to wireless devices. On March 11, ShakeAlert will be activated to deliver alerts directly to wireless devices in Oregon when earthquakes strike.
The delivery date coincides with the 10th anniversary of the magnitude-9.1 Great Tohoku earthquake in Japan, which took about 20,000 peoples’ lives. This quake was the strongest in Japan’s history and struck below the North Pacific Ocean, 81 miles (130 km) east of Sendai, the largest city in the Tohoku region. The quake caused a tsunami that produced waves up to 132 feet (40 m) high and caused the meltdown of three nuclear reactors at the Fukushima Daiichi Nuclear Power Plant.
After traveling across the Pacific, the tsunami rose to more than 26 feet (5 m) in Hawaii and more than 6.5 feet (2 m) in California and Oregon, causing debris to wash up on the Oregon coastline. A task force made up of state and federal agencies, along with non-governmental organizations, worked together for three years to coordinate nearly 900 clean-up events during which an estimated 40,000 volunteers picked up more than 446,000 pounds of debris on the Oregon coast.
Alert delivery using the WEA system will go live on March 11, with a WEA demonstration for educational purposes planned for July 2021 to allow time for Oregon, USGS and partners to broadly promote the system and effectively train the public on how to opt into the test and participate in a statewide alert experiment.
“Oregon is one of the most earthquake-prone areas in the continental United States, and over the years, we have had many earthquakes – large and small,” said Althea Rizzo, geologic hazards program coordinator for Oregon’s Office of Emergency Management. “Warning resources such as ShakeAlert can help to mitigate loss of lives, severe injury and devastating damage to infrastructure.
May 2021: ShakeAlert-powered alert delivery to wireless devices goes live in Washington. USGS has not announced the details of this event.
Earthquakes in the Pacific Northwest
Japan and the Pacific Northwest have almost mirror-image tectonic settings. Both are susceptible to quakes as one tectonic plate slides under another in a subduction zone.
The Pacific Northwest is susceptible to three main types of earthquakes as its underlying tectonic plates build up stress on faults: deep intraslab tremors that occur within a tectonic plate, shallow crustal quakes, and large megathrust earthquakes on the Cascadia Subduction Zone. The area can also experience episodic tremor and slip events, which can release energy equivalent to at least a M7 earthquake.
As the Juan de Fuca Plate spreads away from the Pacific Plate and plunges beneath the North American Plate, it’s strained as it’s bent and pulled by gravity into the Earth’s mantle. When the strain builds to a breaking point, earthquakes as deep as 25 to 43 miles (40 to 70 km) can occur within the Juan de Fuca Plate roughly every few decades; these quakes tend to happen beneath western Washington state.
There have been three deep intraslab quakes with magnitudes greater than M6.5 to hit the region since 1949: the M6.8 Nisqually quake on February 28, 2001, the M6.5 Puget Sound quake in 1965 and the M7.1 Olympia quake in 1949.
Shallow crustal earthquakes tend to occur less frequently than deeper intraslab quakes in the Pacific Northwest, but when they do happen they can be more damaging because of their shallow depths and proximity to densely populated cities. Some quakes are so shallow that they can break or deform the ground surface while others are up to 22 miles (35 km) deep and may not be connected to faults that we see at the surface.
The M6.8 to 7.5 Entiat earthquake in 1872 in central Washington and the approximately M7.5 Seattle Fault earthquake 900-930 A.D. are two examples of crustal earthquakes in the Pacific Northwest.
Lastly, the Cascadia Subduction Zone is a 600-mile (1,000 km) long megathrust fault with a history of large M8 to M9 earthquakes. It stretches from Northern Vancouver Island to Cape Mendocino, California, and separates the Juan de Fuca and North American plates.
Subduction zone earthquakes are the largest earthquakes in the world and reach magnitudes greater than 8.5. The last known megathrust earthquake in the Pacific Northwest was in January 1700 and was estimated to be M9. Looking at geological evidence, scientists estimate that these great earthquakes have occurred at least seven times in the last 3,500 years, which make them likely to happen on average every 400 to 600 years.
Earthquake Early Warning for the Pacific Northwest
In 2012, the Pacific Northwest Seismic Network, which is an Advanced National Seismic System regional network operated by the USGS, the University of Washington and the University of Oregon, joined the earthquake early warning efforts that began in California in 2006.
Incorporation of the PNSN into ShakeAlert extended the USGS ShakeAlert Earthquake Early Warning System across the entire U.S. mainland Pacific Coast, which grew to include support from the Gordon and Betty Moore Foundation, the City of Los Angeles and the state governments of California, Oregon and Washington.
Residents in most locations throughout the Pacific Northwest, including Seattle, Portland, Tacoma, Newport (Oregon) and Eureka (California) should expect that most alerts they receive will be from nearby shallow crustal and intraslab earthquakes.
The vast majority of these alerts will be for earthquakes smaller than M7. In these scenarios, ShakeAlert users who will experience strong (or worse) shaking should expect warning times of less than 10 seconds after which it becomes difficult to take protective actions because of the intense shaking.
In these quakes, there will be a region near the epicenter where shaking arrives before the alert. People should take protective actions as soon as they feel shaking whether they have received an alert yet or not.
