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Study Suggests Heat, Drought Triggered 2014 Napa Valley Earthquake

LOS ANGELES (CBSLA/AP) — "Earthquake weather" is often dismissed as not a real phenomenon, but a new study suggests a combination of drought and heat may have caused an earthquake that hit the Napa Valley in 2014.

When the magnitude-6.0 earthquake hit the Napa and Sonoma Valleys in the summer of 2014, it 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 in the valleys sinks and contracts.

The amount of the horizontal stretching measured is tiny — about 3 millimeters (0.12 inch) — but enough to stress faults, according to the researchers.

"We think it's more of a localized effect, something related to the groundwater system. We don't know if it is groundwater pumping specifically, or something related to how the natural aquifer system works, or a combination," said lead author Meredith Kraner, formerly of the Department of Geosciences at Stony Brook University in New York and now with the University of Nevada, Reno.

A damaged nuilding is seen in Napa, California after earthquake struck the area in the early hours of August 24, 2014. California's governor Jerry Brown declared a state of emergency Sunday following a strong 6.0-magnitude earthquake that seriously injured three people including a child and ignited fires in the scenic Napa valley wine region. The US Geological Service said that the quake was the most powerful to hit the San Francisco Bay area since the 1989 6.9-magnitude Loma Prieta earthquake. AFP PHOTO/JOSH EDELSON (Photo credit should read Josh Edelson/AFP/Getty Images)

Amid the drought, water agencies put further stress on the land as they pumped more groundwater, putting extra stress on the West Napa fault system, possibly triggering an earthquake.

Southern Californians debate endlessly on whether there is such a thing as earthquake weather, which could be anything from unusually hot and humid weather to simply odd tinges to the sky. According to the USGS, there is no such thing as earthquake weather because, statistically, there an equal distribution of earthquakes in all weather.

(© Copyright 2018 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)

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