As we discussed back in February, while we were in the throes of our wettest winter in recent memory, weather like we had can potentially have seismic effects, triggering earthquakes when the ground becomes extremely saturated. That has been mostly theory, however, and now a new study published in the journal Science today provides some of the clearest evidence yet of the role that water may play in causing increases in seismic activity.
From the abstract:
To find out whether precipitation was playing a role, geophysicist Christopher Johnson, a recent Ph.D. graduate from the University of California, Berkeley, set out with colleagues to gather data from a network of 661 GPS sensors scattered around the state. The units are sensitive enough to detect when the ground rises or sinks by a few millimeters because of water weight, groundwater pumping, and tides, among other things. The scientists then teased out how much of those fluctuations came from water being added to or subtracted from Earth’s surface, and calculated how that affected forces deep underground where earthquakes begin, or nucleate. Those force changes were matched with a catalog of nearly 3700 California quakes between 2006 and 2014.
As it turns out, snow and rain can act as "weights" pressing down on mountains, and the gradual lifting of that weight appears to affect earthquake frequency along faults.
The Chronicle picked up the story, and as they summarize:
Johnson and his research partner Roland Bürgmann, a UC Berkeley professor of earth science, found that seismic activity is as much as 10 percent greater in late spring and summer in the Sierra, owing to snowmelt followed by receding water levels in the ground along the coast in summer and early fall.
While the uptick is modest, the research marks headway in the difficult science of earthquake prediction. The thorny endeavor has had limited success in using such things as weather and faraway geologic activity to forecast local and potentially dangerous temblors, but the water cycle may offer new hope.
Most of the earthquakes studied as part of this effort were under 3.0 in magnitude, but Johnson is studying whether water weight might have an effect on larger earthquakes as well.
Johnson tells the Chron, “It’s not like we’re [necessarily] seeing an earthquake season, but the timing of this water unloading is when we’re [historically] getting more earthquakes.”