By Tommy Hough
Here's the news. We can't predict earthquakes, and we're never going to predict earthquakes. Earthquakes aren't like the weather where you can accurately predict a storm system or pressure ridge. Seismology is made up of real-time guesses and predictions based upon models, and while scientists know what happens during an earthquake, they still can't tell you when one will happen.
With earthquakes, you can have a general idea as to when something may occur and apply a likelihood to it, but until the earthquake actually happens there's no way to know. It's all about the application of pressure, and predicting when something will break as a result. If you're stretching a rubber band, you know that eventually, given enough force, the rubber band will break and collapse – thereby turning potential energy into kinetic energy.
With the headlines from last week, you may have missed the news of an earthquake swarm beneath the Salton Sea last Monday and Tuesday very near the San Andreas Fault, which runs along the east side of the Salton Sea. The quakes themselves were centered along an area of slippage along the Salton Trough, a remarkable geologic feature in of itself where California is slowly being peeled away from North America, and which is responsible for the Sea of Cortez and the "low" deserts along the Colorado River. In fact, the "bowing" of the earth's surface as a result of this geologic action results in several large areas of below sea level elevation in the Imperial and Coachella valleys, and the Salton Sea – the result of an engineering accident in 1905 – is one of those areas.
Last week's quakes were frequent and intense enough – numbering about 150 and hitting an average magnitude of 4.0 – to cause some alarm in the Imperial Valley, where a similar earthquake swarm kept residents rattled four years ago in the summer of 2012. But this most recent swarm was so intense it got the attention of the California Office of Emergency Management, which in turn sought the advice of scientists at the state Earthquake Prediction Evaluation Council.
According to the council, the earthquake swarm raised the possibility of a major jolt along the southern San Andreas within the next seven days – but only by an infinitesimal amount – from three-tenths (.03) of a percent of a major earthquake hitting within one week, to a full one (1) percent chance. Not exactly a robust likelihood.
Nevertheless, the California Office of Emergency Management said the data warranted a highly unusual advisory of a forthcoming shock along the San Andreas. According to Dr. Pat Abbott, professor emeritus at San Diego State, the numbers were far too small to issue what was akin to an earthquake warning.
Granted, we are incredibly overdue for a major earthquake on the southern San Andreas or San Jacinto fault systems in Southern California. The last major quake on the southern San Andreas was in 1857 and centered near Paso Robles, while the last major jolt on the San Andreas south of Tejon Pass – which today is the summit of the Grapevine along I-5 near Frazier Park – was over 300 years ago.
The large San Jacinto Fault passes through the northeast corner of San Diego County near Borrego Springs, and heads in a northerly direction past Temecula through the town of Anza in the foothills of the San Jacinto Mountains in Riverside County. There is some argument about whether the San Andreas is slowly transferring its "weight-bearing load" to the San Jacinto Fault, but except for the 6.5 Borrego Mountain earthquake in 1968, which occurred on the Coyote Creek branch of the San Jacinto Fault, the fault itself has been notably absent on major earthquakes for the least 100 years – yet it continues to slowly creep northward, building up stress every inch of the way.
The Imperial Valley's namesake Imperial Fault also appears to be a branch of the San Andreas system. The Imperial Fault Zone has been responsible for pair of damaging earthquakes in Imperial County in historic times, including a 7.1 magnitude jolt in 1940, and a 6.4 magnitude quake in 1979, which resulted in the failure of the multi-story Imperial County Services building in El Centro. The Imperial Fault is also likely related to the Laguna Salada Fault – which caused the big Easter Quake in Baja in 2010.
But despite the proximity of the Rose Canyon and Elsinore faults to San Diego, it's the San Andreas which still holds the most fascination – and results in the occasional warning from concerned parties. Yes, a swarm of 150 small earthquakes along an earthquake fault does raise the possibility of a larger earthquake to follow, and could be foreshocks of a larger event. But when exactly that event will happen remains wholly elusive. We'll know when we know. Hopefully not in the next five minutes.
So get some water, food, batteries and anything else you need now, and get smaller kits for your car. In the event of a major quake, have a plan – and prepare to be without electricity or phone service for a minimum of three days, and prepare for a longer duration of time before you have running water or flushing toilets again.
As a sign in an Army Navy store I used to shop at in Seattle reminded patrons: "Get your earthquake kit now. When you need it, we won't be open."
A former San Diego broadcaster and media personality, Tommy Hough is a wilderness and conservation advocate, communications professional, California Democratic Party delegate, and the co-founder and former president of San Diego County Democrats for Environmental Action.