Yesterday's quake was the largest earthquake in 25 years while in the midst of a record drought. Is there a connection?
The best that scientists can give right now is a "maybe."
The Napa quake has brought new light to a study published earlier this year in the journal "Nature" that found a potential link between quakes and an increase in groundwater pumping.
A team of researchers from Western Washington University found a lack of water in the valley was decreasing the weight on -- and maybe destabilizing -- the San Andreas Fault.
The opposite theory certainly has support.
John Rundle, professor of Physics and Geology at UC Davis, points to a growing belief that hydraulic fracturing for oil has lead to smaller shakers in the Midwest.
Other research also recently found that the depletion of groundwater -- which is heavy -- has led to slight elevation growth across parts of the Western United States.
Rundle says that's more likely to have led to a change in seismic conditions.
Bottom line: Human actions may have some sort of effect on faults, the extent is just unknown.