It is well known that California, located in the United States, frequently experiences earthquakes due to the numerous faults present in the state, including the famous San Andreas Fault. Earthquakes occur when both sides of a fault unexpectedly slide against each other, resulting in tremors that can happen as frequently as 10,000 times annually in southern California alone. However, researchers have found that there is another factor to consider: water.
In a study published in the June 2017 issue of the Journal Science, Christopher Johnson and Roland Bürgmann, seismologists from the University of California Berkeley, discovered that snow and winter rain are largely responsible for numerous earthquakes in California, including those caused by the San Andreas Fault. This phenomenon, known as "seasonal loading," occurs when snow and rain reach the ground in the winter, pressing against the earth's crust. When the snow melts and water moves downstream in the summer, the ground recoils, similar to a tectonic rubber band, activating small earthquakes.
Johnson and Bürgmann found that the mass of winter precipitation causes the Sierra Nevada Mountains to decrease by about one centimeter and the Coast Ranges to decrease by almost 0.5 centimeters. For nearly a hundred years, seismologists have been interested in understanding how different natural forces can affect the earth's crust and cause earthquakes. Tidal movements in the ocean and intense rainfall in the Himalayas have both been known to cause small earthquakes, and large earthquakes in one part of the world can even cause earthquakes in other areas.