Believe it or not, humans are to blame for the small earthquakes occurring in one part of Central California.
These quakes are believed to be the result of the same forces behind the sudden increase in the elevation of Sierra Nevada and Coast Ranges in the past years. A recent study published in the journal Nature unearthed an underlying reason behind the disturbing tremors. It could be because the ground near the mountain ranges is sinking.
The researchers of the Western Washington University (WWU) who conducted the study discovered that excessive amounts of groundwater being pumped out for agricultural irrigation in the farming basin of Central Valley has drastically sunk the area, and they estimated that the mountain ranges near Central Valley have shot up to six inches already since the year 1860 when the practice started.
So how does this contribute to the small earthquakes? As per researchers, groundwater is unlike any forms of water. It is incredibly heavy that its weight puts an immense pressure on the Earth's upper crust. Should the pressure be lifted, the crust abruptly "springs upward," hence, triggering the quakes. In the case of the entire Central Valley, the amount of water lost from the pumping is so large it could fill up Sierra Nevada's Lake Tahoe.
With the use of Global Positioning System or GPS, researchers analyzed the data to find out how human activity affects the mountain ranges in California. What they found out, though, as they dug deeper into their findings, was more alarming that it seemed.
The "ups and downs of the mountains and valleys" total to around one to three millimeters annually, which is mainly due to changes in the seasons. This may affect the San Andreas Fault running parallel to the San Joaquin Valley, the largest fault system in the world. Scientists have found that this fault system is quite sensitive to small-scale changes. During rainy or snowy seasons, the weight of the downpour puts a downward pressure on the Earth's crust. Come summer and fall, heaps of frozen water evaporates, hence, lifting the pressure.
"The real importance of this research is that we are demonstrating a potential link between human activity and deformation of the solid Earth, which explains current mountain uplift and the yearly variation in seismicity," said Colin Amos, assistant professor of geology at WWU. "These are questions that lots of geologists have been puzzling over, and it's a real eye opener to think that humans are the ultimate cause."
The sinking of an area, or land subsidence for a more technical term, is affecting other parts of California as well. In one of Central Valley's major watershed systems known as the San Joaquin Valley, for example, land has sunk to almost nine meters since 1925. That is about five Americans with average height place on top of the other. It also a perennial problem in California since it has also damaged tunnels, bridges and canals throughout the state.
