Dear Fault, could you please wait until October?

Earthquakes are a frequent topic of conversation here in Santa Barbara where I'm spending the summer months doing research. California is a region of high seismic risk and the San Andreas Fault, which runs through the state, is believed to have accumulated enough strain to produce the next big Californian earthquake (or “Big One” as people call it around here). As you can imagine, I wasn't at all amused to be reminded that a quake of magnitude 7 or more might be coming my way. At least today's lunchtime chat brought to mind all the interesting stuff I learnt about geology back in school.

So why is it that the ground beneath our feet shakes every now and then? The outermost layer of our planet is divided into pieces called tectonic plates that are in constant (but slow and imperceptible) movement. The boundaries of these blocks, made up of many faults, rub against and bump into each other. The edges of the plates are rough and tend to get stuck together while the plates themselves keep on moving. This builds up pressure at the faults where the energy that results from the deformation of the moving plates is stored. When two plates have moved far enough apart to overcome the friction between their boundaries, the stored energy is released and an earthquake occurs. As for the San Andreas Fault  – just a few miles east of where I'm currently living – it is “locked and loaded”, as the director of the Southern California Earthquake Center puts it. I can only hope that it doesn't decide to release its energy while I'm here.

photo: David K. Lynch