Potential applicability of the radiation-corrected empirical Greens function to the multi-time-window method

Slip inversion is one of the useful method which can estimate the detailed spatio-temporal slip distributions by solving the inverse problem. In this method, the accurate Greens functions are required, and therefore, we proposed radiation-corrected empirical Greens function (EGF) by correcting the radiation patterns of the EGF seismograms, which can reduce the constraint of the theoretical Greens function and the conventional EGF. Specifically, we correct the amplitude of the EGF seismogram for each of P, SV, and SH waves using the ratio of the radiation patterns in each component at each station based on the ray theory. In our previous study, the effectiveness of the radiation correction was confirmed assuming a point source, and therefore, we next investigate the applicability of the radiation-corrected EGF to the multi-time-window method (Olson and Apsel, 1982; Hartzell and Heaton, 1983) assuming a point source and time expansions. Practically, we applied this radiation-corrected EGF and the conventional EGF to the real data to confirm the superiority of this method. We investigated the reproductivity of the synthetic waveforms and the estimated moment using the observed waveforms for some Mw~5 class earthquakes in Japan inland area. We used the underground observed waveforms recorded by the KiK-net stations of National Research Institute for Earth Science and Disaster Resilience within the epicentral distance of 45 km from each of the target event. To calculate the radiation pattern, we estimated the take-off and incident angles by ray tracing in a horizontally-layered structure of the JMA2001 (Ueno et al., 2002) using the TauP package (Crotwell et al., 1999). As a result of the real data application, we confirmed that the better moment estimations with better waveform fittings can be obtained by the radiation-corrected EGF compared to the conventional method for the three cases. In addition, we evaluate the effect of the uncertainties of the source parameters and the velocity structure, whose errors lead to the worse radiation correction.