Federal nuclear regulators have delayed their review of PG&E Corp.'s application to relicense its Diablo Canyon power station on the central California coast to give the utility more time to complete a seismic review of fault zones that run close to the plant.

The utility, Pacific Gas & Electric, had asked the Nuclear Regulatory Commission for additional time to assess the vulnerability of two reactors to earthquakes in the wake of the nuclear meltdown at Japan's Fukushima Daiichi plant. Diablo Canyon has been the focus of much attention in the wake of the March accident, because, like Fukushima, the plant is close to the Pacific Ocean in a region known for seismic activity.

The commission, in a letter to PG&E sent Tuesday, agreed to postpone its review in part until the 3-D seismic studies can be completed. The new license for the 2,300-megawatt facility had been on track for final approval in 2013, but the delay is likely to push that timeline back by two years or more.

In a request sent to NRC in April, PG&E acknowledged the political pressure to revisit the plant's seismic status before relicensing can proceed, which had been spearheaded by Rep. Lois Capps (D-Calif.) and Sen. Dianne Feinstein (D-Calif.), among others.

John Conway, PG&E's chief nuclear officer, said the company was trying to respond to "many in the public" who requested a pause in the process.

"We know that many of our customers and government partners are concerned and want to know more about the seismic characteristics surrounding the Diablo Canyon nuclear power plant," he said.

In 2008, PG&E and the U.S. Geological Survey discovered a new shoreline fault close to the plant that had not yet been studied in detail. The company says it is working with the State Lands Commission, the California Coastal Commission and San Luis Obispo County to expedite permits and complete the study by the end of 2015.

Because NRC still intends to proceed with a safety evaluation report for Diablo Canyon while the seismic study proceeds, some lawmakers close to the process were critical of the federal commission for not completely applying the brakes to the lengthy relicensing process.

Capps, whose district is home to the plant, also issued a cautionary statement following the NRC decision.

"I don't believe this action goes far enough to guarantee the safety and security of the people living in San Luis Obispo County, which is my number one concern," she said. "The NRC must ensure that critically important seismic information will be a part of this review process. Until it is, the NRC should not let this process go forward."

State Sen. Sam Blakeslee, a Republican from San Luis Obispo, in a statement slammed NRC for not halting the process altogether.

"It's deeply troubling that the all-critical safety evaluation report will be issued before the newly discovered shoreline fault is scientifically analyzed," he said "The vague assurances that supplemental reports might be filed at a later date demonstrates the NRC has learned nothing in the aftermath of the Japanese nuclear disaster."

Sullivan is based in San Francisco.