Earthquakes are highly destructive when they strike, and unlike many other natural disasters, they often hit with minimal warning. Unlike hurricanes and floods, and even volcanoes to an extent, earthquakes can be very difficult to predict. However, in recent decades, warning networks have proliferated around the world, aiming to protect affected communities from the worst outcomes in the event of a large tremor.
ShakeAlert is the name of the earthquake monitoring project run by the United States Geological Survey, which has just announced that it now offers early warning services to the entire west coast of the United States. Let’s take a look at how earthquake monitoring works, how that feeds into early warnings, and how this can make a difference in the case of a major quake.
Seconds, Not Minutes
When an earthquake begins at a geological fault line, it produces a variety of types of waves, known as primary waves (P-waves), secondary waves (S-waves), and various types of surface waves. P-waves travel at roughly 5-8 kilometers per second, around 1.7 times faster than S-waves, and rarely cause major damage. Surface waves are typically slower again. Thus, by monitoring seismographs for characteristic P-waves, it’s possible to get an advance warning that nastier shakes are coming.
ShakeAlert works by detecting faster-travelling P-waves from an earthquake, before the more damaging S-waves hit. It can then send out warnings via phone, radio, and TV, and trigger automatic safety shutdowns across affected areas.
Depending on the distance from the seismograph to the quake’s epicenter, the warning time can be anywhere from a few seconds to a minute or two at most. In the case of Sha ..
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