12:30 PM - 12:45 PM
[STT13-13] Effect of local heterogeneous conditions on growth curves of P-wave
Keywords:heterogeneities, Born approximation, EEW, scattering, growth curve of P-wave, B-delta method
In this study, we theoretically calculate P waves in heterogeneous medium considering the conversion waves between P and S waves, which were ignored in the preceding studies while they give major effect on P-wave envelopes. We show that variation in condition of heterogeneities (in concrete correlation distance) changes the B value. In other word, regional conditions of heterogeneities make the different B values of a given epicentral distance. Then we compare the theoretically calculated B value with one calculated from earthquakes in 1996 - 2011 observed by the K-, KiK-net in Japan. We calculate a regional parameter of heterogeneities (correlation distance) in Japan which can account the fluctuation in the observed B values. As a result, it is found that the spatial distribution of the correlation distance (Figure 1) shows similar tendency with that of a parameter reflecting local heterogeneities, like coda-Q.
In this study we hypothesize that variation in the condition of heterogeneities makes the B value fluctuate significantly and verify it. If we treat the fluctuation in the B values by considering the local condition of heterogeneities, estimation on epicentral distances becomes more accurate. It will improve accuracy of the EEW. Furthermore, B values, that is, initial curve of P-waves can be an exploration tool for local heterogeneities. The early portion of P-wave has a strong advantage that the Born approximation can be used. Complex heterogeneities can be treated by the simple equation.