New Stand-Alone and Advanced Earthquake Early Warning Systems Designed to Protect Railways

Abstract

A new earthquake detection and warning system that uses single station records was designed. The system determines the location and magnitude of an earthquake and issues an alarm immediately after arrival of the P wave (primary wave or longitudinal waves). In the conventional system now in use with Shinkansen (“bullet”) trains, magnitude is first determined and then distance is evaluated. In the new system, the distance to an epicenter is initially determined, followed by the magnitude. Findings have shown that the initial rate of increase in P-wave amplitude is inversely proportional to the epicentral distance. This relation can be used to estimate the distance in a time interval as short as 2 or 3 s after arrival of the P wave. Then an estimate of magnitude can be made from the maximum amplitude observed within any given time interval after P-wave arrival. This method is preferable to the conventional one because larger earthquakes involve longer rupture times, and it is questionable whether magnitude can be estimated correctly in such a short time after arrival of the P wave. Another new system uses earthquake early warning (EEW) information. The Japan Meteorological Agency (JMA), which has a seismic network that covers all of Japan, is responsible for routine earthquake and tsunami observations. The new system receives EEW information from JMA together with the information obtained by railway facilities, executes a risk assessment for the areas concerned, and issues an earthquake warning if necessary. The system could effectively cover most of Japan, and the reliability of the information provided may be far better than that produced by the standalone system. Also, the system could significantly improve outcomes to early adjustments of train operations in the event of an earthquake.