How does Apple's mobile phone have its own earthquake alarm function?

Iphone comes with an earthquake alarm to turn on:

Mobile phone: iPhone 1 1

System: iOS 14.5. 1

1. Click to open the phone settings.

2. Find "Notice" in the settings and click Enter.

3. On the notification page, we can see the following "Emergency Express", just click the switch at the back.

Principles of earthquake early warning:

After the earthquake, the weak P-wave travels fast and can reach the ground first, and the early warning system will be notified. The cause of the earthquake is the sudden rupture and dislocation of rock mass several kilometers to several hundred kilometers underground. The energy released by these faults and dislocations radiates to the surrounding areas in the form of seismic waves. Seismic wave is a kind of mechanical wave, which has a certain propagation speed. When an earthquake happens, we must wait for the corresponding seismic waves to spread to people's places. This time difference leaves room for earthquake warning.

When an earthquake occurs, a P wave that vibrates up and down appears first, with a small amplitude. It takes about 10 seconds to 1 minute for the horizontally moving S wave to arrive, causing serious damage. Earthquake early warning is to use the time difference between P wave and S wave after earthquake.

In principle, the early warning information is received before the earthquake 10 second in the area within 50 kilometers of the focal point; Areas within 90- 100 km can receive early warning information more than 20 seconds in advance. According to the data, accurately estimate the magnitude and epicenter location, and quickly estimate the impact of the earthquake on the early warning target.