Big Quakes in California Possibly Triggered by Oil Production, Study Says

The Western States Petroleum Association, an industry trade group, says there is no evidence of a link between present-day oil activity in California and earthquakes. Here, pumpjacks at work in Bakersfield, Calif., in January 2015. Photo: Jae C. Hong/Associated Press

Some of the biggest earthquakes that rocked Southern California during the early 20th century were possibly triggered by oil production, according to a new study published Monday.
The U.S. Geological Survey study, based on historic oil-drilling records kept by the state as well as quake archives, comes amid public and scientific scrutiny of the potential connection between industrial activity and earthquakes.
Earthquakes tied to the disposal of wastewater from oil and gas production by injecting it into the ground have rattled Oklahoma, Texas and other oil-producing states in the central part of the country.
Between 1920 and 1933, four earthquakes measuring more than magnitude 5 may have been induced by activities related to oil production, according to the study published in the Bulletin of the Seismological Society of America.
One of those quakes, the 6.4-magnitude Long Beach quake of 1933, killed 115 people.
Scientists say records show drilling took place nearby and shortly before each event.
“A common theme we found was when they drilled down to rock,” said Susan Hough, a USGS geophysicist who co-authored the study.
The USGS released maps earlier this year that for the first time show the potential risk of man-made as well as naturally occurring earthquakes, with some parts of Texas and Oklahoma now at the same danger of temblors as California.
Unlike those quakes, which the USGS has said may be caused by wastewater disposal wells, Ms. Hough said the Southern California earthquakes could have resulted from an imbalance in subterranean pressure that resulted after oil was removed from near fault lines.
She said separate studies have shown no link between drilling and earthquakes in the Los Angeles area in the second half of the century, when an improved technique was used to extract oil.
The Western States Petroleum Association, an industry trade group in Sacramento, Calif., said there is no evidence of a link between present-day oil activity in California and earthquakes.
“A multitude of recent scientific studies suggest there is no correlation between the production of petroleum in California and seismic activity,” said Catherine Reheis-Boyd, president of the association.
“Modern industry innovations, along with increased reporting and monitoring, have combined to ensure energy production in California remains safe and efficient,” she said.
The latest findings could alter the way seismologists  have viewed earthquake activity in one of the nation’s most active seismic areas.
By removing those early 20th century quakes as naturally induced, “it does call into question what the rate of natural earthquakes in the L.A. Basin really is,” Ms. Hough said. “Maybe the L.A. Basin as a geological unit is more seismically stable than we’ve estimated.”
Write to Jim Carlton at jim.carlton@wsj.com

http://www.wsj.com/articles/big-quakes-in-california-possibly-triggered-by-oil-production-study-says-1477966625