A federal nuclear inspector urged U.S. regulators to shut down a California nuclear power plant until tests showed its reactors could withstand shocks from nearby earthquake faults, according to the Associated Press and an environmental group.

Michael Peck’s call to close the Diablo Canyon Power Plant in San Luis Obispo County was in a report he made to the Nuclear Regulatory Commission in 2013, the AP reported on Monday, a day after a strong earthquake shook California’s Napa Valley region.

Peck was the lead on-site inspector for five years at Diablo Canyon, which has two reactors designed to produce about 18,000 gigawatts an hour (GWh) of electricity annually, or 7 percent of California’s electricity use. It is owned by Pacific Gas & Electric Co (PG&E).