But new research from the USGS suggests that human-induced earthquakes may not be such a new phenomenon. Research published in the Bulletin of the Seismological Society of America suggests that several earthquakes in the Los Angeles area between 1920 and 1933 may be attributable to oil and gas drilling in the region, reports Annie Sneed for Scientific American.
USGS researchers Susan Hough and Morgan Page scoured newspaper accounts, data from early seismic instruments and scientific surveys to learn as much as they could about early 20th century quakes, focusing on the largest—and thus best documented—of the bunch. From this data they estimated their magnitudes and epicenters.
They found that oil and gas drilling occurred near the epicenters of four major quakes in the LA area, and could have played a role in setting off the temblors. In all cases, the drilling extended down at least 3,000 feet, which was particularly deep for that day and age.
“What they showed is that the conditions are such that the earthquakes could well have been triggered by oil pumping activity,” David Jackson, professor emeritus of seismology at the University of California, Los Angeles, tells Sneed.
And the quakes were not minor. Sneed points out that the 1933 Long Beach earthquake was 6.4 magnitude, killing 120 people and causing $50 million in damage. The other quakes in the study include the 1920 Inglewood quake, 1929 incident in Whittier and 1930 Santa Monica earthquake. Other researchers have determined that it’s unlikely there were any human-induced earthquakes in the area after 1935, well after the peak of oil drilling, according to a press release.
Last year Hough and Page released a similar study, suggesting that oil and gas development in Oklahoma may have caused several earthquakes during the 20th century, including the 5.5 magnitude 1952 El Reno quake and 1956 Tulsa County earthquake.
The research, however, doesn't apply to the current problems with fracking—which usually triggers the temblors when drillers inject wastewater deep into the earth—since the technology and geology of focus regions is so different. But if the earthquakes were human-induced, it means the LA area may not be as earthquake prone as currently believed, Hough explains.
“If you take our four—the 1920, 1929, 1930 and 1933 earthquakes—out of the calculations as induced or potentially induced, it does call into question what the rate of natural earthquakes in the L.A. Basin really is,” she says. “Maybe the L.A. Basin as a geological unit is more seismically stable than we've estimated.”
Though it's entirely possible that drilling could have caused earthquakes in California, the problem is geologically complicated, Thomas Heaton, director of the Earthquake Engineering Research Laboratory at the California Institute of Technology who was not involved in the study, tells Rebecca Hersher at NPR.
"The tricky part of the equation in California is that earthquakes occur regularly without fluid injection," he says. “It would be no surprise to discover that some of our California earthquakes were triggered by oil production. What would be surprising would be to discover that a team of scientists was able to present a compelling case that it had occurred in any particular example.”
Researchers are also unsure if there is a size limit when it comes to manmade quakes, Hough tells Sneed. The record in Oklahoma clocked in at 5.8 magnitude, and some researchers believe the cap may be around 6.0. But Hough says the 6.4 Long Beach quake could change this thinking.