California’s Drought May Increase Earthquake Risk
Most of us probably didn’t feel the 4.2 magnitude earthquake off the coast of southern Oregon Friday morning, but even the smallest quakes serve as a reminder to many of the devastating nature of the “big ones.”
A recent study from the Nature journal shows that there is a strong correlation between earthquakes and California’s current drought. As groundwater from the San Joaquin Valley is pumped out faster than it can be replenished, it increases the risk of seismic activity along the San Andreas Fault.
California’s current drought, which was declared in 2011, is having a severe impact on the agricultural industry, as well as the environment. But a study published by the journal, Nature, shows the wide range of consequences that human activity can have on local seismic activity.
The Study: The Impact of Droughts on Earthquakes
Researchers noticed that the southern Sierra Nevadas and the Coastal Ranges were rising one to three millimeters a year, or about an inch per decade. They began tracking the movements using a string of GPS sensors planted along the base of the mountain ranges. They speculated about possible causes, but no particular theory stood out.
Satellite data over the last ten years showed that groundwater in California’s Central Valley was being depleted faster than it could refill. Colin Amos, a geologist at the Western Washington University in Bellingham, speculated that the groundwater depletion may be connected to the growing mountain ranges, according to the San Francisco Public Press.
Think of a tarp after a rainstorm, weighed down in the center with rainwater. As the water evaporates, the weight on the center of the tarp decreases, and the tarp flattens out.
The earth’s surface works in the same way, and like the tarp, as the water is depleted from the center, the surface rises. According to the study, this seems to have the capability of triggering earthquakes. Furthermore, research showed that seasonal patterns of small earthquakes correlate with changes in seasonal water usage in California.
The team of researchers studied the effect this would have on the San Andreas Fault, which spans roughly the length of California, and found that while groundwater depletion won’t likely cause the “next big one,” it does illustrate the consequences of fault destabilization over time – a trend that will inevitably have drastic consequences.
The San Francisco Public Press reported that Andrew Michael, a geophysicist at the United States Geological Survey in Menlo Park speculated that while the studies help geologists understand the mechanics of the San Andreas Fault, they are not particularly useful in predicting the next big earthquake, according to CBS.
Bracing for the “big one”
Although the depletion of groundwater has a low probability of triggering the next big earthquake, there is no doubt amongst the scientific community that the “big one” will occur – it’s just a matter of when.
With the memory of the 1989 Loma Prieta earthquake still fresh in many San Franciscan’s minds, the idea of the “big one” hitting an unsuspecting San Francisco is terrifying.
Retrofitting much of San Francisco’s vital infrastructure has become the focus of earthquake preparedness throughout the city. Every structure from the Bay Bridge, to the Transbay tube is, or already has undergone retrofitting to ensure that it withstands the Bay Area’s next big quake.
Additionally the San Francisco public utilities commission is still tackling the daunting task of renovating the city’s aging system of reservoirs, pipelines, and canals.
Aging structures, such as the San Francisco General Hospital, have also become the center of concern in recent years for fear that they may not withstand the a major quake.
In 2011, San Francisco Mayor Edwin Lee wrote in a S.F. Examiner editorial, that since 1989, “almost 200 of the city’s buildings and facilities have been seismically retrofitted to improve their performance and the safety to the public.”
Lee is joined by many officials who stress the need for residents to have a specific plan, and to stock up on emergency goods that may prove useful in the wake of natural disaster.