Evaluation of the real-time earthquake information system in Japan

[1] The real-time earthquake information system (REIS) of the Japanese seismic network is developed for automatically determining earthquake parameters within a few seconds after the P-waves arrive at the closest stations using both the P-wave arrival times and the timing data that P-waves have not yet arrived at other stations. REIS results play a fundamental role in the real-time information for earthquake early warning in Japan. We show the rapidity and accuracy of REIS from the analysis of 4,050 earthquakes in three years since 2005; 44 percent of the first reports are issued within 5 seconds after the first P-wave arrival and 80 percent of the events have a difference in epicenter distance less than 20 km relative to manually determined locations. We compared the formal catalog to the estimated magnitude from the real-time analysis and found that 94 percent of the events had a magnitude difference of ±1.0 unit. Citation: Nakamura, H., S. Horiuchi, C. Wu, S. Yamamoto, and P. A. Rydelek (2009), Evaluation of the real-time earthquake information system in Japan, Geophys. Res. Lett., 36, L00B01, doi:10.1029/2008GL036470.