(U.S. Geological Survey)
There are three categories of earthquakes, all of which occur here.
• Shallow or crustal quakes happen along faults near the surface, up to about 10 miles deep. Such faults include the Mount St. Helens Seismic Zone, the Lacamas Creek Fault and the Portland Hills Fault. Shallow faults can trigger by themselves, or could be triggered by deeper earthquakes created through plate tectonics.
• Interplate quakes happen when one geologic plate affects another, such as parts of Juan de Fuca melting and scraping beneath the North America plate. Those quakes tend to be deeper, perhaps 30 miles below Earth's surface.
• Subduction zone earthquakes happen when plates stick and then suddenly slip against one another at plate boundaries, such as the Cascadia fault.
Every year, the Pacific Northwest Seismograph Network records about 2,000 earthquakes in Washington and Oregon. Most are shallow quakes with magnitudes of less than 3.0.
Larger shallow quakes are far less frequent but can be dangerous. The strongest shallow quake recorded since white settlers came to the region was an estimated magnitude 7.4 back in 1872. It was felt in Oregon, Idaho and Washington. More recently, the "Spring Break Quake" on March 25, 1993 -- a shallow magnitude 5.6 centered southeast of Portland -- caused $28 million in damage.
Interplate quakes can cause even more damage. On Feb. 28, 2001, the magnitude 6.8 Nisqually earthquake centered 32 miles beneath the Puget Sound region killed one and injured 700, creating between $1 billion and $4 billion in damage.
Scientists think both of those types of earthquakes happen at a rate of about one per 50 years in the Pacific Northwest.
A 3.7 magnitude earthquake about two miles northeast of Amboy was widely felt in the Vancouver-Portland metro area according to the U.S. Geological Survey.
The quake struck at 5:03 p.m. at an estimated depth of 4.7 miles. The magnitude was originally estimated at 3.5, but the intensity was upgraded twice, to 3.7, within the first few minutes of the temblor.
Shaking was reported in a wide area of Clark County, including Yacolt, northern areas of Vancouver, Battle Ground, Salmon Creek, Northwest, Hazel Dell, Orchards and Washougal.
No damage has been reported, and no emergency calls resulted from the quake, according to the Clark Regional Emergency Services Agency.
A community-generated intensity map compiled by reports to the USGS website reported light shaking. Did you feel it? Report to the USGS here.
As of about 5:45 p.m., almost 800 Clark County residents had responded to the U.S. Geological Survey's "Did you feel it?" website, which sorts the responses according to ZIP codes; about 470 of those who reported feeling the quake live in Vancouver. The most distance response was from Lummi Island, about 190 miles away.
Seth Moran, a seismologist with the USGS' Cascades Volcano Observatory in Vancouver, said Wednesday's quake was a tectonic earthquake. That means it was caused by the squeezing and grinding of plates, not by the movement of magma. The earthquake's epicenter is outside the Mount St. Helens seismic zone, Moran said.
There have been similar events in Southwest Washington before, Moran said. Smaller quakes often spring from the many "microfaults" that criss-cross the entire region, he said. Those tend to produce relatively minor events, Moran said, but not always.
"Every once in a while, they produce a larger event that has the potential to damage things," Moran said.
Wednesday's quake was the largest in the area since a 4.3-magnitude earthquake shook near Mount St. Helens on Valentine's Day in 2011.
While clearly noticeable to people nearby, a 3.7-magnitude quake like Wednesday's doesn't relieve much pressure in the plates that cause it, Moran said. But such events should keep people alert, he said.
"They're mainly just reminders that we live in a seismically active area," Moran said.
Patrick and Eva Woelfel live on Northeast 412th Circle in Amboy, about 300 feet northeast from the earthquake’s epicenter. They were heading home from Battle Ground when the ground shook, but Patrick said they didn’t feel a thing. Nothing in their home looked to be damaged or displaced either.
“We must have a pretty sturdy house,” Patrick said.
Julia Anderson, former Columbian business editor, lives in a rural area five miles northwest of Amboy on Grinnell Road. She thought she heard a tree fall, so she and her husband put on their rain coats, went outside and looked around. They didn’t find any fallen trees.
“We came back in and turned on the TV and saw it was an earthquake. Then on Facebook, everybody was talking about it in minutes.”
“It wasn’t a tree. It was the earthquake. It made a big crack noise. It sounded like a giant fir tree had crashed to the ground and it shook the house. The interesting thing for me was the noise. It was a cracking sound. It sounded like something really split.
Anderson said she’s been in a couple of other small earthquakes “Five on the Richter scale—and neither of them were like this one. It was the noise that was different, “ she said. “It does make me think that maybe I should put together an emergency kit.”
Battalion Chief Tim Dawdy was sitting at his desk inside Clark County Fire & Rescue’s station on North 65th Avenue in Ridgefield.
“It went through like a wave and made a banging noise as it went through,” Dawdy said.
At Clark County Fire District 10 in Amboy, near the epicenter of the quake, Capt. Cheryl Roush felt the earthquake hit. "It was kind of like a thump," she said, "like something hit the building, and then it rattled things and stopped."
Her station hasn't received any reports of damage or injuries, Roush said. She hasn't fielded any calls from people seeking information about the quake either.
Crews with North Country EMS felt the rumble at their station in Yacolt but have not received any emergency calls from the earthquake, said paramedic Mark Widlund.
A few people called Fire District 3 in Hockinson, wondering what happened.
“It was a big boom and a rattle, but it was very short," said Chief Steve Wrightson. "It was unusual for an earthquake."
While a firefighter in California Wrightson responded to emergency calls following a 6.8 magnitude earthquake in El Centro, Calif.
Tom Dixon, who lives in Amboy, said the earthquake sounded like a loud bomb went off in his neighborhood.
"It felt like an explosion," Dixon said. "The whole house rocked. It got our hearts beating, I know that."
Kris Ritton, owner of Earthquake Protection Services in Battle Ground, said he and his wife felt a "very sudden and quick" jolt.
"My wife came in and said 'that was an earthquake, right?' and I said yeah," Ritton said.
Right after the quake, several people in the area called his company, which does earthquake mitigation for offices, hospitals and other businesses in the area, he added.
"I don't think it shook long enough or hard enough to do any damage," Ritton said. "It was pretty shallow, so it was probably a crustal fault. I don't think the shaking lasted long enough to get anything moving."
That said, he advises checking homes for cracks in the morning when there's more light.
"It's certainly possible that people may find some minor damage in the next 24 hours," Ritton said. "A couple years ago we had one in Battle Ground that caused a few cracks."
Walter and Christine Pienkowski said they heard what they thought was an explosion and felt their house, which is northeast of Battle Ground, shake briefly.
Walter Pienkowski said the explosion sounded a bit like an amplified version of "when you put gasoline on a fire to start a wood pile."
It shook the floor of their home, the couple said.
"I was in the '72 earthquake in Los Angeles and this one felt different," Christine Pienkowski said. "It felt like the earth made a big shift and it continued to roll. It was more than I've felt here before."
The couple has lived in Clark County for 30 years, she said, adding that she was surprised it wasn't a higher magnitude.
"I thought it was more like a 4.5, but that's totally subjective," she said.
Jim Flaherty, a retired Vancouver Fire Department firefighter, said he felt a jolt sometime around 5:05 p.m. He lives northwest of Dollars Corner, east of Ridgefield, he said.
"I just turned on the news and I was sitting down and I heard a boom," Flaherty said. "The whole house made a lateral shake, two pictures hit the carpet. It was literally that quick."
Flaherty, who grew up in the San Francisco Bay area, is no stranger to earthquakes, but said the jolt surprised him.
"It was like one big lateral shake," he said, adding that it felt like more than a magnitude 3.5.
The quake was initially estimated at a 3.5, but has been upgraded to a 3.6, then a 3.7, according to the USGS.
There are reports of feeling the earthquake as far north as Woodland. Firefighters felt the quake hit while they were in the station. There have been no reports of damage from the community.
Twitter users responded quickly:
@scancouver -- Wow it was an earthquake! It was teeny though. I thought it was my stupid upstairs neighbors
@ahockley: Brief but noticeable shaking in Sifton...
@rzschomlerJust had an earthquake shake us up in #ridgefieldwa. Big enough to feel our chairs moving and plants and other things shook.
@greerjacob So then what I felt was an earthquake!? I thought the library was going to collapse!
Dawdy reminds people to keep 72-hour emergency kits on hand, equipped with non-perishable food, bottled water, a first aid kit and basic sanitation supplies.
“Water is the biggest issue,” Dawdy said.
Many residents in North Clark County get their water through wells. When the power goes out, they don’t have running water.
Bottled watered shouldn’t be stored on concrete floors, as the lime in the cement can destroy plastic over time, Dawdy said.
Craig Brown, Eric Florip, Tyler Graf, Stover Harger III, Patty Hastings, Susan Parrish, Paul Suarez, Ashley Swanson, Sue Vorenberg contributed to this story.