The staff members of the Japan Meteorological Agency (JMA) monitor earthquakes in Tokyo, the capital of Japan, on May 11, 2010. [Xinhua]

The Japan Meteorological Agency (JMA) provides residents in Japan with earthquake early warnings.

The Earthquake Early Warning system issues prompt alerts just as an earthquake starts, providing valuable seconds for people to protect themselves before strong tremors arrive. The system announces the estimated seismic intensities and expected arrival time of principal motion.

These estimations are based on prompt analysis of the focus and magnitude of the earthquake using wave form data observed by seismographs near the epicenter.