Earthquakes occur when the tectonic plates of the earth’s crust shift, jolting past each other in a release of built-up tension. However, other natural forces can also influence seismic activity: Hydrological dynamics, like changes in groundwater and snowpacks, in particular, put pressure on faults. A new study from Caltech finds that a higher rate of change in groundwater levels leads to a noticeable increase in seismic activity. … Utilizing new data analysis methods, the researchers saw that regions experiencing more dramatic changes in groundwater levels exhibit a larger seasonal variation of seismic activity. In Northern California in particular, groundwater changes correlated with an increase in seismic activity of up to 10 percent.