Many people are already aware that earthquakes frequently shake the state of California in the United States of America. The Golden State is marked by numerous faults, including the infamous San Andreas, an extensive crack in the crust of the Earth which is 800 miles long and where the Pacific and North American plates meet. Tremors — about 10,000 times annually in just southern California solely — happen once both sides of a fault slide unexpectedly with each other. However, researchers state that there is one other thing that needs to be put into the equation: water.
On one research released in the June 2017 issue of the Journal Science, Christopher Johnson and Roland Bürgmann, seismologists from the University of California Berkeley, stated that snow and winter rain are relatively responsible for numerous earthquakes in California, including the ones brought about by the San Andreas Fault. It is a science phenomenon the two seismologists refer to as “seasonal loading.”
Seasonal loading happens once snow and rain reach the ground during winter and presses towards the crust of the Earth. Once snow melts and water moves downstream during summer, the pressed ground recoils – or contracts – similar to a tectonic rubber band, activating tiny earthquakes in the process.
“The accumulation of snow and water in the mountains and basins during the rainy winter months causes the ground to be pushed down; then during the summer the ground pops back up as the snow melts and water flows down rivers or otherwise goes into the ground,” Johnson says in an email. “This flexing of the crust acts to clamp and unclamp the faults. For the San Andreas, we find the clamping effect during the winter and an unclamping during the late summer.”
Johnson and Bürgmann exclaim that the mass of winter precipitation reduces the Sierra Nevada Mountains by approximately one centimeter or 0.4 inches, and at the same time, stream and groundwater reduces the Coast Ranges by nearly 0.5 centimeters or 0.2 inches.
For almost a hundred years, seismologists have pondered on how various natural forces influence the crust of the Earth and the onset of earthquakes. The tidal movements of the ocean, for example, have been documented to cause frail, small earthquakes in the deepest regions of the San Andreas Fault line. The same can be said with intense rain falls in the Himalayas Mountains. Likewise, very large earthquakes in any part of the Earth can cause earthquakes in other parts of the planet as well.
In The Golden State, seismologists have consistently pondered on the question whether there exists a small upsurge in seismic occurrences alongside the San Andreas Fault during summer and fall – the most dried up periods of the year. There are parts of the San Andreas, for instance, where the earthquakes are extremely feeble – about magnitude 2 — that Americans won’t even feel their presence.
Using information collected from a total of 661 GPS sensors spread all over California, the two seismologists calculated the vertical movement of the fault lines. The sensors used were especially responsive and had the ability to sense the faintest sinking and raising of the ground. Christopher Johnson and Roland Bürgmann analyzed 3,600 earthquakes from 2006 to 2015. Both completed the necessary calculations, computing the earthquakes once stress on the faults was at its highest level. On top of that, Johnson and Bürgmann examined history books and investigated bigger earthquakes, magnitude 5.5 or higher, that have shocked California starting from 1781.
Once they examined the results, Christopher Johnson and Roland Bürgmann discovered a pattern: The moment water gathered from snow packs, lakes and reservoirs throughout the course of the winter, its mass depressed the crust of the Earth. As a natural reaction, the ground recoiled once water levels reached their lowest levels during the summer season, creating minor earthquakes. Based on these findings, the two seismologists made the conclusion that tiny quakes happened about 10% more than regular once seasonal loading was high.
Image Source: Simone Migliaro / Shutterstock