On June 24, at 8:10am Pacific time, a magnitude 5.6 earthquake struck Northern California. Later that day, at 6:04pm local time, a back-to-back quake, magnitudes 7.2 and 7.5, struck northern Venezuela.
The first quake did little damage; the second was devastating. Both quakes triggered similar mobile phone-based alert-system warnings. But how those systems detected the quakes was about as different as the quakes themselves.
Both systems are based on the fact that the speed of light is much much faster than the speed of an earthquake. If the quake can be detected quickly, a warning can be sent to the cell phones (and other devices) in the vicinity at essentially the speed of light. Even a few seconds warning can make a big difference.
Detection is the key, and that’s where the two systems differ. The U.S. west coast’s ShakeAlert system, active since 2019, relies on thousands of large ground sensors. The detection system in Venezuela, the Android Earthquake Alert System, relies on millions of cell phones and their tiny built-in accelerometers.
ShakeAlert costs tens of millions of dollars and is run by the USGS. Android Alert is crowdsourced and run by Google. Both systems are quite innovative and make interesting case studies (stay tuned).
In 1989, Alan and colleagues rode out the Loma Prieta earthquake on the fourth floor of an Apple building in Cupertino. Many others were in Candlestick Park in San Francisco, awaiting the start of the World Series. A few unfortunate souls were on the Bay Bridge and elevated highways.
The up to 20 seconds warning they all might have received with the current systems could have made a big difference. Hopefully it did in Venezuela.