A new study suggests oil drilling decades ago may have triggered earthquakes in the Los Angeles region, including the deadly 1933 quake.
Scientists from the U.S. Geological Survey identified 13 quakes in the 1920s and 1930s that may have been caused by the industry, including the 1933 Long Beach quake that killed more than 100 people.
Researchers say drilling techniques have changed, so the findings don't necessarily point to a current risk.
Deadly quakes triggered by energy drilling are rare. In 1984, a magnitude 7 quake in Uzbekistan linked to gas extraction killed one person and injured 100.
Man-made quakes have been in the spotlight after a sharp rise in quakes in Oklahoma and Texas. Studies have linked the increase to the practice of injecting leftover wastewater into the ground.