Experts research central Pa. 'earthquake swarm'

The Associated Press

DILLSBURG, Pa. - Residents in Dillsburg, York County, have experienced about 600 small earthquakes over the last year, and now researchers have released a 20-page report looking into why.

Earthquake expert Charles Schamberger is one of the researchers. He says most of the earthquakes are happening where there are two different types of rocks in contact with each other. The rocks in the area are already weakened by mining, and they can slide.

Schamberger teamed up with other earthquake experts and Columbia University to study the Dillsburg quakes. They term the 600-plus events an earthquake swarm.

Schamberger said in other earthquake swarms, the little quakes were not followed by big ones.