Napa, California - As the second anniversary of the August 24, 2014 South Napa earthquake approaches, U.S. Geological Survey scientists and volunteers, along with faculty and students from California State University, East Bay are planning an experiment to visualize the subsurface in and around the City of Napa and measure how the ground responds to earthquake shaking in different neighborhoods.
Hundreds of small portable seismographs will be temporarily set out along lines that cross the West Napa Fault zone and most of the Napa Valley. The data gathered will help characterize the underground geology around the West Napa Fault and the Napa Valley in three dimensions. This type of seismic survey can yield information that helps characterize localized shaking effects during an earthquake, and can help the community prepare for future earthquakes.
Very small explosive “bangs” set off at the bottom of 20-30-foot-deep drill holes allows seismic energy (tiny artificial quakes) to travel through the subsurface geological layers, allowing researchers to gather information about these layers that can’t easily be learned any other way. These tiny artificial earthquakes can only be felt if one is standing within a few feet of the drill hole.
Throughout August and early September, USGS scientists and volunteers will be in Napa-area neighborhoods, surveying locations to place the seismic instruments that will record the tiny explosions. Actual deployment of the instruments is planned to be during the last week of August and early September.