COLUMBUS, Ohio (AP) — A new study suggests fracking triggered hundreds of small, unnoticeable earthquakes in eastern Ohio late last year, months before the state first linked seismic activity to the much-debated oil-and-gas extraction technique.

The report, which appears in the November issue of the journal Seismological Research Letters, identified nearly 400 tremors on a previously unmapped fault in Harrison County between Oct. 1 and Dec. 13, 2013.