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. The work is published in the journal Science Advances.