The cause of loud booming sounds that have shaken houses in and around Port Angeles, Washington over the past week remains a mystery.

Possible explanations range from naval exercises in the Strait of Juan de Fuca to thunderstorms in the Olympic Mountains.

The Canadian Navy confirmed that the HMCS Edmonton was conducting gunnery exercises with a .50-caliber machine gun in the Strait on Thursday -- but not any other day of the week -- from 10 a.m. to 4 p.m.

But that wouldn't explain why people, such as Marie Barclay of Port Angeles, had her house shaken by loud booms Tuesday and Wednesday.

"It was pretty loud, like a sonic boom," she said.

"All you heard was the boom, and I didn't hear an airplane or nothing like that."

Canadian Navy spokeswoman Lt. Commander Natalie Garcia said that the gun used in Thursday's exercises would sound like a rifle and not an explosion.

The sound wouldn't shake a house on the North Olympic Peninsula, she said.

Garcia said no other Canadian naval exercises have occurred in the Strait this week.

She said U.S. Coast Guard Sector Seattle had the joint-naval exercise area about 3 nautical miles south of Vancouver Island and north of Twin and Pysht reserved from July 24 through Wednesday for gunnery exercises.

But a spokeswoman for Coast Guard Sector Seattle said no such exercises took place this week.

"That's really bizarre, actually," said spokeswoman Tara Molle.

"As far as the on the Coast Guard side, for us, we don't have any training going on up there."

Mike Allen, operations unit controller at Coast Guard Group/Air Station Port Angeles, said the station has not conducted any exercises that would explain the sound.

Allen said he also has heard the loud booms this week.

The Canadian Coast Guard also said it's not the cause.

National Weather Service meteorologist Brent Bower said there were thunderstorms in the Olympic Mountains on Wednesday.

Seven to 10 days

But Georgia Wawro, who lives near Port Angeles High School, said she has heard the loud booms for the past seven to 10 days, including on Thursday.

"It doesn't sound like thunder" or fireworks, she said.

Wawro said she has heard the booms once or twice a day, possibly originating from across the Strait.

"It's not shaky enough to be a sonic boom, but it still rattles my windows," she said.

Clallam County Planning Manager Steve Gray said there has been no quarry blasting or any other permitted explosions this week.

Navy spokesman Sean Hughes said the Navy has not conducted any exercises in the area this week.

A spokesman for McChord Air Force base in Tacoma said he couldn't provide information on flight records in the area without knowing the exact time when loud noises were heard.

But he said the Air Force is not allowed to break the sound barrier, which would create a sonic boom, over populated areas.

The Navy's Blue Angels are in Seattle this week for Seafair, but spokesman Petty Officer Peter Carnicelli said they fly only over Lake Washington and, like the Air Force, the planes not allowed to break the sound barrier.