Millions of people worldwide, including in California, Japan, and Venezuela, have received mobile phone warnings in recent earthquakes, providing precious seconds to seek safety. These early earthquake warning (EEW) systems, varying in sophistication and reach, are designed to detect seismic waves and alert populations before the most damaging ground motion arrives.
Several nations have implemented their own EEW systems. These include the United States, Mexico, Japan, Turkey, Romania, China, Italy, and Taiwan, according to the U.S. Geological Survey (USGS). While Venezuela does not have a national EEW, some residents received alerts through Google's Android Earthquake Alerts system, which has expanded significantly since its 2020 rollout.
The Android system leverages accelerometers in smartphones. When a stationary phone detects initial P-waves, the fastest but least destructive seismic waves, it sends data to Google's detection center. This crowdsourced information is analyzed alongside data from other phones to confirm an earthquake and trigger alerts to users in the affected area. Richard Allen, director of the Berkeley Seismology Lab, stated that the system now reaches over 2.5 billion people globally, alerting approximately 60 earthquakes each month to an average of 18 million phones.
Pericles Sánchez, a Venezuelan writer in Caracas, reported receiving an alert minutes before an earthquake struck, allowing him to evacuate his home safely. Similarly, a Venezuelan migrant in Bogotá, Colombia, received an alert on his phone about quakes near his hometown, highlighting the system's reach even across borders.
In the United States, the USGS operates the ShakeAlert system along the West Coast, covering California, Oregon, and Washington. Launched in 2019, ShakeAlert has issued 6.8 million alerts for 194 earthquakes. Robert de Groot, a USGS scientist, emphasized the importance of multiple warning methods, comparing it to carrying a spare tire or cash.
The principles behind most EEW systems involve detecting seismic waves. P-waves arrive first, followed by the more destructive S-waves, and finally the most destructive L-waves. By detecting the P-waves, systems can transmit electronic signals—which travel at the speed of light—to warn people before the slower-moving S-waves arrive. The warning time is typically short, with those closer to the epicenter receiving the least amount of notice, or sometimes no warning at all.
Established systems like Mexico's, which began public alerts in 1991, utilize broadcast stations, phone apps, and public alarm systems, alongside regular earthquake drills. Japan's system is considered among the most sophisticated, having expanded to include underwater sensors and cables after the devastating 2011 earthquake and tsunami. This expansion, known as the Seafloor Observation Network for Earthquakes and Tsunamis (S-Net), uses thousands of miles of undersea cables to monitor offshore subduction zones, reportedly increasing warning times by about 20 seconds and tsunami warnings by up to 20 minutes.
While these systems offer crucial lead time, their effectiveness can vary. Some individuals may receive multiple alerts for a single event, while others, particularly in more remote areas, might not receive any warning.