Dozens of aftershocks have occurred since Sunday's magnitude-6.9 earthquake that rattled Northern California, the state's largest temblor in nearly a decade.
The largest of the aftershocks, near Ferndale in Humboldt County, measured a magnitude 4.5, and officials expected them to continue for several days. Overall, the aftershocks have been getting smaller and less frequent.
Sunday's quake caused no damage or injuries because it was centered 50 miles off the coast of Eureka and occurred at a depth of "10 miles beneath the Pacific seabed," according to the U.S. Geological Survey.
By the time the seismic energy reached the shore, it had dissipated significantly. The USGS said the North Coast felt only moderate to light shaking.
By contrast, a 6.5 quake hit the area in January 2010, snapping power lines, toppling chimneys, knocking down traffic signals, shattering windows and prompting the evacuation of at least one apartment building.
The North Coast sits along the Mendocino Triple Junction, where the Pacific, North American and Juan de Fuca tectonic plates collide. It is one of the most seismically active parts of the San Andreas fault system that runs through the state. In 2005, a magnitude-7.2 quake struck off Northern California.
On the California mainland, the two most recent large quakes were the magnitude-7.1 Hector Mine temblor in 1999 and the magnitude-7.3 Landers quake in 1992.
Sunday's temblor, which struck less than 55 miles from McKinleyville, Fortuna, Eureka and Ferndale, was followed by at least 13 aftershocks as large as magnitude 4.6, according to the USGS.
Sgt. Brian Stephens of the Eureka Police Department said that as of about 6:15 a.m. Monday, "we have not had one report of damage anywhere in the city."
"Definitely a change from the last one we had," Stephens said, referring to the 2010 quake that rocked Eureka. "This one was the exact same magnitude almost.... This was a roller, and the other was more or less a violent shaking."
Stephens said it was his understanding the quake, which hit at 10:18 p.m. Sunday, lasted as long as 38 seconds.
"It was definitely a long one," he said.
Stephens was out on a call when the quake struck and said his "car was rocking back and forth."
"I thought someone was shoving my car back and forth, looked around and nobody was there," he said. "Then I realized what was happening."
There were also no immediate reports of damage or injury elsewhere in Humboldt County, and no tsunami warnings were issued.
A resident of Ferndale, Raquel Maytorena, 52, felt the earthquake in her nearly 100-year-old home about a mile from the coast.
"It just kept going and going, very slowly and softly. It was not violent," she said. "It almost felt like you were in a boat that was rocking."