Where: On any seismic region where teutonic plates meet, San Francisco has become a legendary earthquake site.
When: They may occur at any time – warm, dry dates are thought to bring bigger quakes.
Watch Out: stay away from buildings, your car and windows.
Earthquakes are an integral part of everyday life and culture in California… Did you know that dozens of tiny ‘shakers’ rattle the state each week, unfeeling beneath your feet, through the dozens of faults that crisscross the West Coast? Locals take them in stride and although they fear the ‘Big One’ (the predicted catastrophic quake that is expected sometime in the future), small earthquakes are laughed off and joked about (to the amazement of wide-eyed visitors).
San Francisco is more famous for them than LA, having experienced the 1906 and 1989 quakes that devastated the city. The southern part of the state is also full of faults and earthquakes have occurred there, shaking San Fernando in 1971 and Northridge in 1994. While the San Andreas Fault is the primary location for earthquakes in California, (and is so large its visible from the air) dozens of smaller faults are just as dangerous and its these fractures that make the state such an active place, geologically.
What’s An Earthquake?
Earthquakes occur when tectonic plates slip after years of stress and pressure have kept them locked; the resulting shockwaves are the earthquake that is often preceded by foreshocks and followed by numerous aftershocks. The 1989 Lom Prieta quake in San Francisco had more than 30,000 aftershocks and moved the entire San Francisco Bay area by more than 3 feet northwards. The earth is always on the move, from millions of years ago when the world was just one land mass to the many continents we have today.
Strange things can occur when earthquakes strike including liquefaction that causes buildings to sink into their foundations and harmonic resonance where the frequency of the earthquake matches the building’s height and the building is instantly destroyed.
After any major quake strange personal stories also emerge of people thrown off their feet and bounced off walls while seeing 8 foot waves in their swimming pools before the water crashed into the house; others have witnessed 4 ft waves in solid ashphalt and seen ocean waves at the beach actually reverse as the quake strikes. At home people have seen whole walls torn free while crystal glasses a few feet away have survived, and others have seen neighbours houses collapse while they didn’t even lose a single piece of china. Locals also call any dry, hot and totally still days ‘Earthquake Weather,’ (like that on October 17th, 1989) as a perfect time for a shaker.
Predicting And Measuring ‘Quakes’
Quakes are measured on the Richter Scale, which is an exponential scale developed in 1935 by Charles F. Richter. This means that a 6.0 earthuake is not twice as strong as a 3.0; its actually more like 30 times stronger. Ask a Californian after a minor quake what the magnitude was and chances are you’ll get a pretty accurate answer; experiencing these ‘shakers’ so frequently many are able to get the strength on the nose before the geologists do.
Earthquake prediction has not been as successful as hoped, and while speculations as to which fault will slide next do exist, they tend to be percentage chances on specific segments. For example, the fault that slipped in 1989 had a 90% chance of a 7.0 quake in the next thirty years. In that case the scientists were right; but the 1994 Northridge quake came as a complete surprise.
How To Survive An Earthquake
Earthquakes are nothing to be afraid of; if youre lucky (or unlucky) enough to experience one it won’t do more than rattle the windows and teacups than cause injury and will certainly make for a more memorable ‘California’ experience than the earthquake ride at Universal Studios. However remote a chance it is essential to know what to do if the ‘Big One’ or even a moderate quake strikes while youre in California:
If you’re indoors, immediately upon sensing the earthquake move away from windows and heavy furniture and get to a doorway as soon as possible; alternatively get under a sturdy desk and hang on because the shaking can be violent and often involves movement that is side to side, up and down and often all at once. Shield your eyes from falling debris and face away from windows that can explode; cover the back of your neck with your other hand to prevent spinal injuries from falling objects.
If you’re outside, move away from large buildings and lie flat on the ground away from power lines, bridges and tall trees with your hands over your head covering it from debris. If you are driving, stop the car as soon as possible staying away from bridges, overpasses and tall buildings. Stay in your car.
Once the shaking has stopped DO NOT run out of the building as debris can be still falling its better to wait and leave when it is safe. If youre outdoors stay away from buildings in case of aftershocks. If youre driving go extremely slowly as the quake may have damaged roadways.
Every phonebook in California has earthquake safety information and can be a valuable resource if a quake did strike while youre there.
US Geological Survey
Information for the whole of the USA.
Earthquake Hazard Programs – North California
News, real time shaking maps, research and resources.