Seismologists in the Pacific Northwest have been getting a lot of calls in recent days after a major earthquake rattled remote Southern California over the Fourth of July weekend. No one was killed, but the event raised many questions.
The 7.1 magnitude quake in the remote Ridgecrest area was preceded by a powerful 6.4 magnitude foreshock the day before.
INVISIBLE HAZARDS
The earthquake was unusual because it occurred on a new fault that the experts didn’t have on their maps. Erin Wirth, a research geophysicist with theU.S. Geological Survey in Seattle, says some of these deep cracks in the earth don't actually reach the surface.
“So they’re very hard for us to see with our geological or geophysical techniques. And then if there haven’t really been earthquakes that have happened there in the recent past – so they haven’t been recorded – there’s really no way of knowing that the faults are there. It’s very challenging.” she said. “So that’s not an uncommon situation.”
MAJOR FAULTS HERE
Wirth adds that a lot is known about major faults in the Northwest, including the 750-mile Cascadia subduction zone off the west coast. The zone is expected to cause a “full rip” magnitude 9 earthquakeand tsunamiany day now, with devastating effects. There are also several smaller faults beneath Seattle, Tacoma and South Whidbey Island, which could cause major damage.
Wirth says seismic hazard mapping and analysis take these faults into account, but also recognize that earthquakes can happen anywhere.
Authorities are reminding residents to be prepared. That means having enough emergency supplies on hand to live independently for at least 7-10 days. Others are encouraging residents to look into earthquake insurance policies and possible retrofits for their homes.
Wirth says although the Pacific Northwest is definitely earthquake country, residents don’t feel seismic shaking events as frequently as in California. It's been almost two decades since the last major event here: the 6.8 magnitude Nisqually earthquake of February, 2001.
Seeing the effects of the Ridgecrest quake is a wake-up call.
“It is a good reminder that this not only happens in California, but can also happen in the Pacific Northwest,” Wirth said. “It’s a good reminder to be prepared and to continue to do research into these areas.”
SHAKE-ALERT APP COMING SOON
Technology that can help warn residents when an earthquake is hitting is coming soon to the Pacific Northwest. A smartphone app will send an alert seconds before shock waves intensify to dangerous levels.
The same system had its first test in California’s big quakes over the Fourth of July weekend, with mixed results.
The idea is if a quake’s epicenter is miles away, the small window of opportunity to take cover or reroute power or water could save lives or valuable resources in the region.
“The Shake-Alert early earthquake warning system actually is up and running and generating alert messages in our region, here in the Puget Sound area,” said Harold Tobin, director of the Pacific Northwest Seismic Network and a professor of Earth & Space Sciences at the University of Washington. He says beta testers include water districts and the City of Seattle.
A key question before rolling out a smartphone app for the public here is what threshold should be used for alerts. In California last week, many people with the app didn't get an emergency message, because they weren't in a damage zone. But they still felt major shaking and wondered what was happening.
“So perhaps we’d find the sweet spot where it reminds people that the system exists as what to do in an earthquake, without actually making them want to turn it off,” Tobin said.
He says in the Northwest, big earthquakes are rare enough that a lower threshold will probably make sense. But it will be one to two years before the app is released to the public in Washington and Oregon.
