Fig. 3

Example acoustic waveforms (a, b) and spectra (c, d) for vertical (a, c), and northeast-directed (b, d) blasts. Color is representative of the station distribution in Fig. 1. Example polar plots (e, f) show peak spectral frequencies (0–100 Hz with low frequencies in plot center) and station azimuth (1°–360° clockwise from North at the top) relative to the source position (SRC). Squares mark maximum frequency of each spectra as shown (e, f) note for lateral discharge shown in d and f the higher frequencies northeastward and diminished frequencies southwestward. The window onset for a and b is ~ 0.1 s prior to the explosion onset for each experiment