On Monday, NHK started a broadcast service for earthquake warnings (kinkyu jishin sokuho), with private broadcast stations to follow suit. Rather than predict when and where earthquakes will strike, the warnings will tell how many seconds it will take tremors from a major earthquake to reach specific areas. Since a few seconds can make the difference between life and death, it will be important to educate people on what action they should take when they receive such a warning.
An earthquake produces two types of waves: primary waves (P waves) and secondary waves (S waves). P waves, which cause minor tremors, travel faster than S waves, which cause major tremors. The Meteorological Agency's network of seismographs first will detect the P waves and determine the focus and size of the earthquake. It then will calculate in how many seconds major tremors will hit specific areas.
In the event of a major earthquake whose focus is under Suruga Bay, for example, a warning for Shizuoka can be issued about 10 seconds before major tremors hit. Major tremors would hit Nagoya in about 25 seconds, and Tokyo in about 40 seconds. It is estimated that such a quake would cause up to 9,200 deaths. Yet, one simulation shows that a 10-second advance warning could reduce fatalities in Shizuoka Prefecture by up to 80 percent.