Hundreds of millions of dollars have been invested in developing a method to predict where and when the next major earthquake will strike. Unlike weather forecasting, which has significantly improved through the use of better satellites and powerful mathematical models, earthquake prediction continues to fail. But what if you get even a couple of minutes to get away from a nearby earthquake? If you are an Android phone owner and live in a seismically active zone, there’s a chance of receiving an unusual warning.
Since 2020, starting with the US, a system called Android Earthquake Alert (AEA) has been around and is on by default in most Android phones. A few days ago, Google put out a paper in Science about how the system works and what it has seen during the first few years of operation.
Over the last four years, AEA system has detected thousands of earthquakes and “sent alerts to millions of people in nearly 100 countries, often giving them the crucial moments they need to take cover before the shaking arrives”.
Evaluation of thousands of earthquakes, analysis of specific earthquake examples and direct user feedback allow the system to continuously improve its performance in key areas, like magnitude estimation, making the alerts more effective over time.
The aim of the system is not to replace traditional seismic sensors. AEA can offer a scalable, low-cost early warning tool for regions without dense scientific networks, making it promising for developing countries where smartphones are common but seismometers are rare.
Smartphones have accelerometers that allow them to sense changes in motion. It is the sensor that allows phones to figure out how many steps you’re walking. When the phone is placed on a table, the accelerometer doesn’t register significant motion. But when you walk or if a truck is going outside your house, the phone’s accelerometer can pick up such vibrations/activities. The same goes for less subtle vibrations of earthquakes.
“If a stationary phone detects the initial, faster-moving P-wave of an earthquake, it sends a signal to our earthquake detection server, along with a coarse location of where the shaking occurred,” said Marc Stogaitis, principal software engineer, Android.
Google came up with a method for telling different movements apart. It helps alert people with enough time to do something about the impending arrival of potentially destructive seismic waves.
“What if we could give people a few precious seconds of warning before the shaking starts? Those seconds can be enough time to get off a ladder, move away from dangerous objects and take cover,” said Stogaitis.
Once a rough location of where the shaking has occurred is picked up, the system then quickly analyses data from many phones to confirm that an earthquake is happening and estimate its location and magnitude. The goal is to warn as many people as possible before the slower, more damaging S-wave of an earthquake reaches them. The system sends out two types of alerts: BeAware alerts (for estimated light shaking) and TakeAction alerts (for estimated stronger shaking, which take over the phone’s screen and play a loud sound).
Light green areas show the countries where the Android Earthquake Alerts System is currently detecting and delivering alerts. The areas alerted in individual earthquakes are shown in red where there was strong shaking (Modified Mercalli Intensity (MMI) 5+) and yellow for lighter shaking (MMI 3-4). The grey circles indicate other Android detections in regions where alerts were not issued. Android also delivers alerts generated by ShakeAlert in California, Oregon and Washington (dark green). Picture: Google Research
To receive alerts, users must have Wi-Fi and/or cellular data connectivity, and both Android Earthquake Alerts and location settings enabled. Alerts are sent based on a privacy-preserving, rough location of the device. Users who do not wish to receive these alerts can turn off Earthquake Alerts in device settings.
According to Google Research, the system has now detected over 18,000 earthquakes, from small tremors of M1.9 to major quakes reaching M7.8. For the events significant enough to warn people, alerts were issued for over 2,000 earthquakes, culminating in 790 million alerts being sent to phones worldwide.
“The impact has been a ~10x change in the number of people with access to EEW systems. In 2019, only about 250 million people had access. Today, thanks in large part to the Android system, that number has increased to 2.5 billion,” said Stogaitis.
The paper published in Science says that user feedback shows that “85 per cent of people receiving an alert felt shaking, and 36, 28, and 23 per cent received the alert before, during, and after shaking, respectively.”