STATE CENTER — For several years in a row — and always on Dec. 31 — Marshall County residents have reported a loud explosion shaking houses in the area to mark the turn of the calendar. On Sunday, it happened a few hours earlier than in years past, and later in the day, State Center Police Chief Jon Thomas told the T-R he had a theory as to the origin of the mysterious boom.

“The boom is more than likely the same individual or group of people using tannerite or similar products with firearms,” he said. “The amount necessary to create this much energy would be significant, but we are aware of no other reasonable explanation for this event repeatedly year after year on the same day than this.”

Two years ago, Marshall County Emergency Management Coordinator Kim Elder speculated that the noise was the result of a “frost quake” but conceded last year that it was unlikely a natural phenomenon would occur on the same day every year. Thomas added that the explosions were “likely occurring” outside of the city limits in rural State Center.

“We do not have more information to share and the event by itself is not criminal, so we will not be conducting any further investigation,” he said.