Six independent earthquakes and two aftershocks of magnitude 4.4 to 5.1 shook Los Angeles between 1935 and 1944, a rate of about one every two years. The area also experienced a higher rate of low-intensity earthquakes during that time frame. After 1945, the rate dropped to one moderate earthquake every seven years.The article's link has an interesting picture of oil derricks right up next to Huntington Beach. Up to 9 billion barrels came out of the ground -- about what the US now produces in years.
Unlike recent earthquakes associated with hydraulic fracturing in Oklahoma, the mid-century events were not caused by deep fluid injection but were likely caused by taking oil out of the ground, according to the new study.The article says the oil companies knew they were causing earthquakes, because of smaller and more frequent earthquakes in their oil fields. ('Course, they didn't pay for the damages they did. Maybe no one complained back then because "oil fueled the growth of Los Angeles from 50,000 people in 1890 to 1.5 million in 1940."