Forest of wells, rigs and derricks crowd the Signal Hill oil fields.

Drilling at sites such as the Signal Hill Oil Field in California may have precipitated earthquakes in the region. Credit: Andreas Feininger/The LIFE Picture Collection/Getty

Geophysics

Oil drilling linked to a spate of Los Angeles earthquakes

A frenzy of drilling may have caused quakes in the first half of the twentieth century.

Oil pumping probably triggered six moderate earthquakes in the Los Angeles area between 1938 and 1944.

As the Second World War loomed, oil companies drastically ramped up drilling in southern California. Rigs sucked up so much oil that in some cities, such as Long Beach, the ground dropped. The resulting pressure and stress changes in the underlying rock probably triggered the quakes, say Susan Hough at the US Geological Survey in Pasadena, California, and Roger Bilham at the University of Colorado, Boulder.

The scientists calculated the rock stresses created by oil production and compared the results with historical records of earthquake damage. The comparison showed that quake locations overlapped with areas where rock stress would have increased because of drilling. If some of these quakes were triggered by drilling, then the number of natural earthquakes in the Los Angeles area may be smaller than previously thought.

In around 1960, oil companies began injecting water into their wells, and the number of triggered quakes declined.