Sundar Pichai received an early warning of an earthquake hitting San Jose

"You may have felt shaking," Google CEO Sundar Pichai and several California residents on Tuesday received this alert as a 4.8-magnitude earthquake hit the San Francisco Bay Area in the US. But what caught all the concentration and generated some stir on social networks was that many users received the alert even before the area in which they suffered the tremors and shakes of the seismic waves.

The mobile alert about the California earthquake was from an app called ShakeAlert, which was developed by Google. Sundar Pichai was one of the thousands of Android phone users who received the alert before the area was hit by tremors. He even shared a screenshot of the Android alert on Twitter and wrote, "The alert came just before, felt like a long one, hope everyone is ok."

Notably, the app does not predict natural disasters but instead analyzes data provided by state government agencies and third parties. The tectonic waves in the earth's crust are always in motion, and when they collide, they generate seismic waves. Sensors installed by the agencies record the data and send it to data processing centres. When recorded waves are high, and damage is expected, the ShakeAlert system reads the information and then sends a notification to alert people.

Interestingly, what happens with these apps is that they can record the information and transmit it to other places close to the speed of light, which is faster than the speed at which seismic waves travel. The result is that people are often given an earthquake warning seconds, sometimes even minutes, before the ground beneath their feet actually shakes.

"Light is faster than seismic waves... seismic waves travel at a speed of around 7km per second. This is a rough calculation, so there could be some plus or minus here and there. Now the distance between Delhi and Kolkata is 1,305 kilometers by air. Dividing this number gives us around 190 seconds. So the first tweets on Kolkata tremors came around 7:27 pm. The Delhi tweets came around 3 minutes later."