An earthquake deep below the mountains of southwestern Oregon could shake up what seismologists know about the types of earthquakes likely to strike in the region, the Mail Tribune reports today. It wasn't the size of the quake, but rather the depth that caught the attention of scientists.
The magnitude 4.1 earthquake was recorded at 1:52 a.m. Thursday in the mountains 30 miles northwest of Grants Pass near the Josephine-Curry county line, according to the U.S. Geological Survey. It happened about 24 miles below the Earth's surface and resulted from the Juan de Fuca plate, a vast slab of basalt on the ocean floor, sliding beneath the North American continental plate, then breaking deep underneath the Earth's surface.
"It's the only one of this kind recorded within miles of that location since 1833," Ian Madin, chief scientist at Oregon's Department of Geology and Mineral Industries, told the newspaper.
No major damage was reported. Safeguard your property from earthquake damage with information from the Institute for Business & Home Safety.
More than 130 people reported feeling this quake on Pacific Northwest Seismograph Network's "Did you feel it?" Web page, according to the newspaper. The bulk of the reports came from Grants Pass, the population center closest to the quake. But the reports of strongest shaking came from the coast in Gold Beach, Agness and Coquille.
"When the source is that far down, it affects a fairly large area and the effect can feel much the same over the whole large area," Bill Steele, a seismologist at the seismograph network's University of Washington office, told the newspaper.
In the Puget Sound, deep earthquakes caused the 6.8 magnitude Nisqually quake in 2001, which resulted in $4 billion worth of damage.
"People had speculated whether that could happen under Oregon," Madin said. "There haven't been well-documented instances, but this could be one."
Scientists might argue about this quake for years, even though it had little effect on people, he said.
"Don't worry about this one," Madin said. "Think of the big Cascadia zone one."
A report prepared last year on the potential for deep earthquakes along the Cascadia subduction zone, a long fault in the ocean floor that separates the Juan de Fuca and North America plates and runs from British Columbia to Northern California, used Beaverton as the most likely location for a massive quake in Oregon.
"There's a higher probability there," said Steele, one of the participants in the Cascadia Region Earthquake Workgroup, which produced the report. "But all of Oregon is earthquake country."