No, that wasn't a dump truck or a jet airplane you felt Saturday afternoon. A mild earthquake centered in the Helena Valley was felt by many in the capital area shortly before 4 p.m. Saturday, prompting many calls to the police but causing no reported damage.

According to Paul Spengler, Lewis and Clark County disaster and emergency services coordinator, the small tremor measured 2.24 on the Richter Scale and lasted a few seconds at 3:53 p.m. Saturday. The focus of the quake was about four-and-a-half kilometers under ground where Tenmile Creek crosses beneath Interstate 15 in the Valley.

"It's not a concern," Spengler said. "That's a minor earthquake. We don't even check the dams until it's (magnitude) 3.5 or higher, and that's still small."

Around 30 people called the police to report hearing or feeling the quake, but none reported any damage.

"The reason this one was felt and heard by so many people despite its small size was because it was so shallow," Spengler said. By comparison, a magnitude 3.5 earthquake 15 miles east of Seeley Lake on Thursday was centered 20 kilometers beneath the earth's surface.

Spengler said reports of people hearing a small quake rather than feeling the ground shake is normal.

"Many people will hear something that sounds like a dump truck rather than shaking. That's typical," he said.