New Streams and Springs after the 2014 M6.0 South Napa Earthquake

Abstract:

At least nine streams and several springs, which were dry or had little flow before the 2014 M6.0 South Napa earthquake, started to flow after the earthquake. At the same time, a USGS stream gauge on Sonoma Creek registered a coseismic increase in discharge. Public interest in the increased flow was heightened by a state of extreme drought in California. The combination of the earthquake and drought provides an unprecedented opportunity to test hypotheses about the origin of the new water because the flows did not mix with pre-existing surface waters and thus preserved their pristine composition. Following the earthquake we repeatedly surveyed the new streams and one spring, collecting data to test hypotheses about the origin of the new flows. We show that the new flows were meteoric in origin and likely groundwater in nearby mountains released by the earthquake. We also simulate the flows and estimate the total amount of new water to be of the order of 10⁶ m³, about 1/40 of the annual water use in the Napa-Sonoma region. Our model makes a testable prediction that seismic velocity in the shallow crust would show a post-seismic decrease.