Available Warning Time for Emergency Response in Sendai City, Japan Against Miyagi-Oki Subduction Earthquakes Based on National and Regional Earthquake Early Warning System

Abstract eng:
Sendai, located in northeastern Japan, is the biggest city in the Miyagi prefecture has about one million population and suffered severe damage by subduction zone earthquakes in history. Last one was, 30 year before, 1978 Miyagi- ken oki earthquake with M 7.4. The occurrence of huge events in this prefecture has the average of 37.1 year and 6 year standard deviation. Therefore this seismically vulnerable city needs urgent strong motion prediction and reliable Earthquake Early Warning Systems. The City is preparing now for Miyagi-ken offshore earthquake and it is crucial to inform society about the warning time of a probable upcoming earthquake so that precautionary actions can be taken by the individuals, government or the companies. This paper describes considerations about various warning time and differences of time intervals between onset time of P-wave to P-wave, P-wave to S-wave, P-wave to PGA, S-wave to S-wave and S-wave to PGA. Their meaning and importance are discussed according to different warning level for two locations. Warning times are first calculated depend on travel time tables of theoretic P- and S- wave velocities and then based on recorded accelerograms with usage K-net. The study indicates that Sendai has 17.3 second in average with 6.4 second standard deviation before the strong shaking reach the city.

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