A 5.8-magnitude earthquake struck off the coast of Oregon late Monday, followed by a swarm of smaller quakes that continued into Tuesday.
The US Geological Survey reported the first tremor at 10:30pm local time (1:30am ET), about 102 miles west-southwest of Port Orford.
At least five additional quakes have been recorded in the same area, the strongest measuring 4.9 magnitude.
‘This event is identified as the potential mainshock of an earthquake sequence,’ the USGS said in its notice of the original larger quake.
The agency estimated a six percent chance that one or more aftershocks stronger than magnitude 5 could strike in the next week, powerful enough to cause damage.
Smaller tremors are more likely, with as many as 50 aftershocks of magnitude 3 or higher expected, strong enough to be felt in the region.
One such tremor, a 3.1 magnitude quake, struck at 1:05am local time (4:05am ET) Tuesday.
The Oregon coast sits along the Cascadia Subduction Zone, where the Juan de Fuca Plate pushes beneath the North American Plate.
This fault system produces frequent small offshore tremors and carries the risk of massive, destructive earthquakes. Scientists have long warned that the zone is overdue for a catastrophic event.
The earthquake hit late Monday evening, triggering seismic activity early Tuesday
The earthquakes hit about 102 miles off the coast of Port Orford (pictured)
In April, researchers at Virginia Tech found that an 8.0 magnitude or higher quake along the Cascadia Subduction Zone, combined with rising sea levels, would cause coastal land to sink up to 6.5 feet within 30 minutes of a major tremor.
They determined that an earthquake of magnitude 8.0 or higher, combined with rising sea levels, could cause coastal land to sink up to 6.5 feet within 30 minutes.
The most severe effects would hit southern Washington, northern Oregon and northern California, some of the region’s most densely populated areas.
This event would result in a significant expansion of the coastal floodplain, an area with a one percent chance of flooding each year, increasing it from 35 square miles to 116.
Such an event would expand the coastal floodplain from 35 to 116 square miles, placing an additional 14,350 residents, 22,500 structures, and 777 miles of roadway at risk.
The Cascadia Subduction Zone has historically produced quakes of magnitude 8.0 or larger every 400 to 600 years, with the last one striking in 1700.
Against this backdrop, Oregon Gov. Tina Kotek on Monday announced new seismic safety rules, just hours before the 5.8-magnitude quake hit.
Kotek’s order requires all new state-owned buildings larger than 10,000 square feet to meet the strictest earthquake standards, while older structures must be upgraded to current life-safety codes by 2060.
The 5.8 magnitude earthquake hit at 10:30pm local time on Monday, just off the coast of Port Orford (pictured)
‘Preparing for an earthquake is a long game,’ Kotek said. ‘If we look at 50 years, we can spread that cost out—replace or retrofit two per cent of our buildings each year, and in 50 years we’ll have upgraded every single one.
‘Yes, it’s a multibillion-dollar effort, but planning it over decades makes the funding challenge more manageable.’
State Rep. Dacia Grayber, a first responder and earthquake-readiness advocate, said, ‘One of the things that keeps me up at night is … we are the only post-industrial region pretty much in the world that hasn’t lived through our worst natural disaster.
‘We’ve seen this train barreling down on us, yet we only react when emergencies start to personally affect us.’
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