One of the aspects that hit the magnitude earthquake 5.2 who shaken the southern California yesterday (he was warned up to Los Angeles), with an epicenter in Julian and a hypocenter at 13 km deep, is the fact that the inhabitants of San Diego (64 km from the epicenter) were notified through about smartphones notifications 14 seconds before of the arrival of the earthquake. This was possible thanks to the system Shakealertdeveloped by the USGS, the US geological service. But how does this system work, and how is it able to send notifications before an earthquake arrives?
Let’s clarify one thing immediately: Shakealert it is unable to predict the seismes (nobody is yet able to predict earthquakes), but it is simply very quick to elaborate the data and send them to the population. The system is active in the US West Coast and is based on a network of across 2000 Sismographers and GPS sensors Distributed in the States of California, Oregon and Washington. These tools reveal the waves pthe fastest generated by an earthquake and generally less intense. When at least 4 of these sensors detect the passage of the same wave, the seismic and position data are immediately sent via wireless to the nearest calculation center which estimates almost in real time the position of the epicenter and the intensity of the earthquake. If you exceed certain estimated magnitude thresholds, the system instantly sends alert messages via Smartphone to the population of urban centers not yet reached by the seismic waves.
In this way, if the distances are sufficient, the inhabitants can know a few seconds in advance that a strong shock is about to arrive and protect themselves. This system is able to avoid extreme consequences and potentially save lives, but to do it it must be extremely quick. In the case of the M5.2 earthquake in California, for example, the messages were sent when the seismic waves on the surface had just traveled 9 km. In this way the inhabitants of San Diego, who is in 64 km from the epicenter of the earthquake, they were notified by Shakealert 13.9 seconds before arrival of seismic waves. The city of Escandido (47 km from the epicenter) has been notified about 9.2 seconds before being hit and Santee (42 km) with an advance of 7.9 seconds about.
Messages are transmitted via system Wireless Emergency Alert for magnitude greater than 5.0, or through the apps of your mobile phone or as Push notifications On Android devices for magnitude greater than 4.5, a bit like the system does It-Alert here in Italy. Below you can see an Alert displayed on an Android device during the M5.2 earthquake in California.
In addition to the notifications directed to the population, the Shakealert system also allows you to activate Automated reactions to infrastructurehow to launch audio warnings through public speakers, stop or slow down trains and open the doors of the firefighters’ doors to facilitate the exit of the trucks.
