A new calculation method is proposed for a real-time seismic intensity indicator (Ir), whose concept is similarly to the JMA seismic intensity (IJMA)defined by Japan Meteorological Agency. With the increasing requirements of earthquake early warning (EEW) system, it is much more obvious that IJMA has a real-time delay since the IJMA needs a filtering operation in frequency domain. In order to improve the real-time calculation suitable for the EEW system, a new real-time seismic intensity indicator, Ir (real-time seismic intensity), is defined by using an approximating filter in time domain instead of the original filter in frequency domain. This indicator, Ir,can be calculated as a time series on real-time and its maximum value, Ia (approximate seismic intensity), corresponds to an approximate value of IJMA. The relationships between IJMA and Ia value are examined by means of using a large number of strong motion records. Results show that Ia value estimates IJMA with reasonable accuracy in wide intensity ranges. For a small computing system like a strong-motion seismograph, it is easier to process Ir than processing IJMA. Therefore, Ir is suitable for using in an EEW system based on the concept of JMA seismic intensity.
