9 earthquakes off Oregon coast ‘not alarming’, says seismologist

A cluster of earthquakes was recorded early Wednesday off the Oregon coast about 300 miles west of Newport but caused no damage, according to the US Geological Survey.

The agency recorded nine earthquakes in five hours, three of them within minutes of each other. The first earthquake was recorded at 2:54 a.m. and was of magnitude 3.8. By 7:01 a.m., eight more had struck.

The largest earthquake in the series occurred at 4:56 a.m. and recorded a magnitude of 5.6, the data showed.

No tsunami threat has been reported, said Joan Gomberg, seismologist with the US Geological Survey in Seattle.

“It’s nothing to be alarmed about, and these are relatively small, especially given their distance offshore,” Gomberg said. “To create a tsunami, the seabed must rise or fall, and in this case the seabed moves laterally.”

According to Gomberg, the earthquakes occurred along the Blanco Fracture Zone, a fault between two tectonic plates that extends about 300 miles northwest of the Oregon coast and tends to generate many small earthquakes.

Gomberg said the Blanco Fracture Zone should not be confused with the Cascadia Subduction Zone, a fault that stretches 600 miles along the West Coast from northern California to British Columbia, and is capable of producing potentially devastating earthquakes of up to magnitude 9.0. The Cascadia Subduction Zone is about 200 miles closer to the Oregon Coast than the Blanco Fracture Zone.

In subduction zones where two tectonic plates collide, forcing one plate under another, plate movement can create mountains and volcanoes and lead to major earthquakes and tsunamis. Tectonic plates in fracture zones, however, move side by side and parallel to each other, resulting in much smaller earthquakes on average, Gomberg said.

“It’s very far from the subduction zone, and a fracture zone is a completely different structure,” Gomberg said. “It’s by no means a truly extraordinary activity.”

— Catalina Gaitan

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