A spate of mysterious booms has been shaking a city in central Oklahoma.

Oklahoma Geological Survey research seismologist Austin Holland says a series of thunderous booms rattled the Norman area at 11:19 a.m. Friday and that numerous more were reported in the same place around the same time Thursday.

Both Holland and National Weather Service meteorologist Matthew Day say they have no explanation for the booms that have been rattling houses and frightening livestock in the city on the southern edge of Oklahoma City.

Holland says there have been no earthquakes close enough to the area to be the cause of the booms. Day says a phenomenon known as cryoseisms (kry-oh-SY'-iz-uhmz) — which occurs when water freezes quickly in soil or rock, then expands and cracks — is also not to blame.