SPOKANE, Wash. — A rock burst that injured seven miners underground may have been triggered by seismic activity in Idaho's Silver Valley, the mining company said Friday.

All the injured miners were expected to fully recover from the injuries they suffered Wednesday. The two most serious injuries were a broken arm and a broken pelvis.

The mine remained closed and the federal Mine Safety and Health Administration is investigating.

Hecla Mining Co. said a small earthquake helped trigger a similar rock burst last month in the same area of the Lucky Friday Mine, one of the deepest mines in the nation.

The latest rock burst was unrelated to two separate accidents earlier this year that killed two miners at the Lucky Friday, Hecla president and chief executive officer Phil Baker said.

Hecla said that on Nov. 16, a small seismic event triggered by blasting in the mine caused a rock burst at roughly the same location as the latest accident 5,900 feet below the surface of the silver mine. No one was injured in that incident, Hecla said.

A rock burst is a common mining accident in which excessive pressure causes a rock to fracture or explode.

There was no blasting in the mine for 24 hours prior to Wednesday's rock burst, Hecla said.

That raised the possibility that a seismic event alone caused the burst.