Some earthquakes in Southern California in the early 20th century, including a temblor that killed 120 people in Long Beach, could have been caused by oil drilling in the area, according to a report by two U.S. Geological Survey (USGS) geologists in Pasadena, CA, that was published Tuesday.
Susan Hough and Morgan Page reviewed historic geological and oil drilling records for the first four decades of the last century, doing geologic detective work to potentially link the deadly 6.4-magnitude 1933 Long Beach quake to deep drilling in an oilfield in nearby Huntington Beach, CA, according to a report published in the Bulletin of the Seismological Society of America.
The Long Beach quake hit not long after operators began drilling wells at different angles, the researchers found. They said the historic findings don't necessarily indicate any current risks in the region today from oil/natural gas drilling, because drilling technology has changed substantially since the 1930s.
Last year, another study by a different team of scientists at USGS and the California Institute of Technology (Caltech) found no significant evidence of human-caused quakes in the greater Los Angeles area after 1935.
Until now, "we pretty much assumed that earthquakes in the L.A. area are natural and that induced earthquakes are either not happening or not significant," said Hough, who led the latest study.
Caltech seismology professor Jean Paul Ampuero characterized the Hough/Page study of past quakes as "a nice piece of seismological detective work," in a report in Tuesday's Los Angeles Times. He confirmed that the results are "speculative" because there were no modern seismic sensors in place in the period of the early 20th Century quakes.
Hough and Page assessed a series of quakes between 1915 and the early 1930s, tying in oil permits and drilling operations during that same time period. They discovered 13 cases of shaking that they concluded may have been caused by the ramping up of oil production.
Their work comes at a time when other USGS scientists have concluded that the injection of wastewater as part of the post-hydraulic fracturing (fracking) process in Oklahoma has contributed to a spate of quake swarms in the state in recent years (see Shale Daily, July 5). Seismologists have found no evidence of anything like that happening in Southern California, which was one of the world's major oil basins in the first half of the 20th Century.
Wastewater injection and fracking in other major shale plays, such as the Bakken in North Dakota, has not stimulated increased quake activity in those states.
Earlier this year a University of Texas and Southern Methodist University study found oil and gas activities over the past four decades are probably linked to at least 59% of induced earthquakes in Texas (see Shale Daily, May 18).
While the latest study could not be conclusive about a link between drilling and the historic Southern California quakes, it raises the possibility and should be further researched, according to independent scientists in the field, such as Frohlich and Bill Barnhart, assistant professor of geophysics at the University of Iowa.