NAPA, California. Research suggests that the magnitude 6.0 earthquake that rocked California’s wine country in 2014 can be caused by an extension of the earth’s crust, because of the season, receding of the groundwater under the Napa and Sonoma valleys.
The vineyard-filled valleys flank of the West Napa Fault, that the earthquake that killed one person, injured several hundred and caused more than $500 million in losses.
The study was recently published in the American Geophysical Union Journal of Geophysical Research: Solid Earth suggests land between the valleys is stretched every summer, as the groundwater levels fall below the valleys, and the soil in the valleys is declining and contracts.
The amount of the horizontal stretch measured is small — about 3 mm (0.12 inch), but enough to stress errors, according to the researchers.
“We think it’s more of a localized effect, something in connection with the groundwater system. We don’t know whether it is the pumping of groundwater, specific, or something related to how the natural hydrological 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.
Co-authors were William E. Holt of Stony Brook University and Adrian A. Borsa of the Scripps Institution of Oceanography at the University of California, San Diego.
The early-morning Napa quake on Aug. 24, was the biggest hit of the San Francisco Bay Area since the magnitude 6.9 Loma Prieta earthquake of October. 17, 1989.
The left 8 miles (12.8 km) of the surface cracks and damaged many historic masonry buildings and older homes, according to the u.s. Geological Survey.