INNOVATION May-June 2014

that can cause buildings and other structures to shake, rattle and collapse. The gap between P-waves and shear waves can be as little as 5 to 15 seconds if the epicentre of the earthquake is nearby, or as much as 45 seconds to 1 minute if it were 150 to 200 kilo- metres away. The problem is, many people tend to ignore the vibrations caused by P-waves. “People who have never experienced an earthquake go into denial when things start vibrating,” Ventura says. “They attribute the vibrations to nearby construction. By the time they realize it’s an earthquake, it’s too late.” And that’s what the earthquake warning system is designed to prevent. These small, ground-based monitors have been assembled and calibrated to detect the P-waves that chil- dren would never notice when they are out on the playground at recess, or even hard at work in the classroom. But with the proper training and the sound of the alarm, they could seek life- saving shelter. “There are earthquakes all the time,” Ventura adds. “We have 3,000 or more small quakes every day. It’s amazing. The earth is shaking all the time. It’s a living entity. The trick is to say at what point that shaking is related to a large earthquake, a magnitude five or higher, or a four right underneath you. That’s when earthquakes start to do damage.” And that’s when the earthquake warning systems now being installed in BC schools may save lives. v

Earthquake early warning system panel providing ground motion signals to UBC’s research facility for computerized assessment.

P-waves are mainly compression waves and do not tend to cause damage to structures. The waves that travel at lower speeds are known as shear waves, or S-waves, love waves and Rayleigh waves, and these

waves tend to cause severe damage to structures. Scientists who study earthquakes refer to these waves as earthquake signatures and ev- ery quake produces its own unique signature depending on how large the earthquake is, how far away the epi- centre is and at what depth the release of energy has occurred. P-waves are compression waves and travel through the earth’s crust extreme- ly fast. They tend to produce slight vibrations at the surface without caus- ing any damage and can be confused with normal human activity. “P-waves are just like a little rattle,” says Ventura. “When you are in your home and a big truck goes by you feel your house shake. You are feeling P-waves being transmitted through the ground and into your house.” Shear waves and their travelling companions, love waves and running waves, are less compressed and travel more slowly, but pack a real punch. As Ventura notes, these waves are the ones

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