Fig. 4

a Spatial distribution of the residuals of the grid search for origin time correction of 1 s. The spacing for the grid search is 2 km (horizontally) and 1 km (vertically). b Observed and synthetic waveforms. The top trace in each pair, denoted as DATA, is the observed ground velocity waveform; the bottom trace, denoted as SYN, is the corresponding synthetic computed for the best source parameters (FAMT). The last character in the component name denotes the direction of motion (N: north, E: east, U: upward). The first 13 pairs from KGS003U to KYK U are short-period waveforms with passband of 4–40 s; the rest (from KGS003U to KYK U) are long-period waveforms with 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 are shown at the top. The obtained source time function (STF) and the moment tensor are also plotted in the bottom right corner. c Comparisons of the 1D and 3D synthetic waveforms and the observed waveforms (see also Additional file 1: Figure S3)