NAPA, Calif. -- New research suggests the magnitude 6.0 earthquake that rocked California wine country in August 2014 may have been caused by an expansion of Earth's crust due to seasonally receding groundwater under the Napa and Sonoma valleys.
The vineyard-filled valleys flank the West Napa Fault, which produced the quake that killed one person, injured several hundred and caused more than $500 million in losses.
The study recently published in the American Geophysical Union's Journal of Geophysical Research: Solid Earth suggests land between the valleys is stretched each summer as groundwater levels fall beneath the valleys and the ground sinks and contracts.
Study lead author Meredith Kraner says the researchers do not know if it's related to groundwater pumping or how the natural aquifer system works - or a combination of both.
For more stories, photos, and video on earthquakes, visit this page.