It prompted the state Public Utilities Commission to order Pacific Gas & Electric Co. to cut natural gas pipeline pressures.
The San Francisco Chronicle reports two of the pipelines are buried under heavily populated areas in the south San Francisco Bay area. The PUC says it ordered PG&E to reduce pressure on the lines by 20 percent below their legal limits.
PG&E said late Wednesday that besides running the four lines above legal limits, the utility intentionally increased the pressure on a dozen pipelines temporarily.
Information from: San Francisco Chronicle, http://www.sfgate.com/chronicle