Effect of local heterogeneous conditions on growth curves of P-wave

It has been adopted empirically that a growth rate of initial P-waves decreases as the epicentral distances become distant. Using this relationship, epicentral distances are estimated from the growth curve of initial P-waves immediately after the occurrence of earthquake in the current Earthquake Early Warning (EEW) system. However the growth rates are not only the function of epicentral distances but also the function of seismic source function, heterogeneous condition of medium, etc. So the growth rates of different earthquakes are fluctuated each other. This fluctuation decreases the accuracy of the EEW. In this study we reveal that a main cause of the fluctuation is seismic scattering and the fluctuation has locality. Finally we propose a robust procedure to estimate epicentral distances considering the locality.