Seasonal rain and snow trigger small earthquakes on California faults

California’s earthquake faults continually accumulate stress until they fail in an earthquake. Seismologists studied the impact of the flexing of Earth’s crust under the load of winter rains and subsequent unloading during summer drought, and found that the up and down movement of the mountains changes the stresses on the state’s faults, making them fail slightly more often as the snows melt and the rivers drain in late summer and early fall.
Geology News — ScienceDaily