Quake rattles area

SANDPOINT — Bonner County was unscathed by the series of earthquakes that occurred on Thursday night and early Friday morning.

“We have no reported damage,” said Bob Howard, director of Bonner County Emergency Management.

Howard said there were reports of down trees, but no significant

structural damage or injuries when the first quake, a magnitude 4.1, occurred at about 7:30 p.m. on April 23.

It was centered about 14 miles southeast of Sandpoint, a preliminary earthquake report from USGS said. It registered at 22 stations and its depth was measured at 5 kilometers.

After the quake, Bonner Dispatch received numerous reports of an explosion from callers in Sandpoint, Sagle, Hope and elsewhere. Residents at Priest Lake and Bonners Ferry also felt it.

Paradise Valley resident Kate Turner wrote on the Bonner County Daily Bee’s Facebook that the second noticeable quake “rocked and rolled,” while Linda Alt, also from the Paradise Valley area, noted that felt the first quake.

Lesser shakes were detected at 10:43 p.m. and at 1:30 a.m. on Friday, according to the U.S. Geological Survey.

Residents Cari and Jimmy Cruse wrote: “We felt it up here in Samuels! Cupboard doors all popped partially open & banged shut a couple times.”

Earthquakes in the Sandpoint area are rare, but not unheard of, said Bill Phillips, a University of Idaho research geologist with the Idaho Geological Survey.

“There is a history of earthquakes in Sandpoint. It’s just that they occur every other generation or so. There was one in 1918 and one in 1942 that are roughly the same size,” said Phillips.

Phillips said there are a number of faults in the area, including the Hope Fault.

“That’s a suspect. And yet having said that, when you go down and stand on the ground and you look at the Hope Fault through a geologist’s eyes, there’s not a lot of indication that it’s broken in the recent geologic past,” Phillips said.

A USGS ShakeMap indicated the April 23 quake could be felt in Boundary and Kootenai counties, in addition to eastern Washington and western Montana.

The most recent earthquake activity in North Idaho was in 2003, when a magnitude 3.3 quake struck near Rathdrum, according to USGS.

An intensity VI shock in 1942 centered near Sandpoint affected 25,000 square miles of Idaho, Washington and Montana. The Northern Pacific Railroad partially suspended operations to make sure boulders and slides were not covering any tracks.

“Church services were interrupted, but only minor damage was reported by homes,” the USGS earthquake almanac for Idaho said.

The largest recorded earthquake in Idaho occurred in 1983, when a magnitude 6.9 earthquake near Borah Peak struck. It caused two deaths in Challis and an estimated $12.5 million in damage.

Speculation was rampant that the temblors were linked to volcanic activity elsewhere in the region or on the globe, but Phillips doubts that it had any influence on the earthquakes here.

“If you have a volcano that has magma moving beneath it that’s moving around, it’ll generate earthquakes for sure. It happens all the time at Mount St. Helens and it’s happening at Yellowstone. But just I just don’t see the connection with Sandpoint,” he said.

Moreover, Sandpoint is not near a tectonic boundary, a subduction zone or

a massive fault such as the San Andreas Fault in California.

Phillips said not a great deal about the Bonner County earthquakes is known.

“One of the reason I say that is we don’t have a lot of seismic instruments on the ground all over the area there. We’re not highly instrumented in Idaho, especially North Idaho,” said Phillips.

Satellite-based interferometric synthetic aperture radar has emerged as a useful tool in earthquake analysis because it can detect minute changes in topography. However, Phillips said those resources tend to be focused on densely populated areas with large, active faults.

Philllips is advocating for further analysis of the shakers in Bonner County and earthquake activity statewide.

“My goal is really to see the science grow to a point where we can answer questions definitively,” he said.

Boundary County residents are asked to share their experiences with the recent quakes on the Herald’s Facebook page.