Fig. 3

a Observed and synthetic waveforms for EV2003. The top trace in each pair, denoted DATA, is the observed ground velocity waveform; the bottom trace, denoted as SYN, is the corresponding synthetic computed for the FAMT parameters. The horizontal components with respect to the FDM grid are used in the FAMT analysis so that the last characters X and Y in the component name denote the directions of the horizontal ground motions (Fig. 1a). The character U denotes upward ground motion. The first two columns from TYS-X to HRO-U display the short-period waveforms with a passband of 4–40 s; the remaining columns display the long-period waveforms with a passband of 10–40 s. The numbers next to each pair denote the maximum amplitude (\(10^{ - 3}\) cm/s) of the observed waveform. The estimated moment magnitude and the normalized residual (F in Eq. 1) are shown at the top. The obtained source time function (STF) and the moment tensor are also plotted in the bottom-right corner. b Same as a but for EV2007. c Detailed comparisons of the observed velocity waveforms (DATA: red) and the synthetic waveforms computed using 3D (blue) and a flat-layered structure model (1D: gray) at station TYS and HRO. d Same as c but for EV2007