A spate of major earthquakes on small faults could overturn traditional views about how earthquakes start, according to a study from researchers at the Centro de Investigación Científica y de Educación Superior in Ensenada, Mexico, and the University of California, Davis.

The magnitude 6 earthquake that shook the Napa Valley in August was the strongest the region had felt in more than 20 years. But the next earthquake in the area could be much stronger, according to preliminary research from the University of California, Davis, presented at the American Geophysical Union conference in San Francisco.