Fig. 4

Pre-eruption and eruption time sequence showing unfiltered WIZ seismic data (a), filtered seismic data 0.03–0.1 Hz showing VLP (b), waveform semblance search over the White Island volcano at 1-min non-overlapping time increments (c), and best fit depth and error bounds based on waveform semblance (d). The blue line in (c) is derived from a sparse grid semblance computation (500 m grid spacing) which reveals periods having strong radial waveform coherence. If the coarse grid semblance (blue line in c) was above 0.6, then a dense grid search (25 m spacing) was completed for pre-eruption (blue dots) and syn-eruption (red dots) periods and refined locations (see Fig. 5) and depths were determined (d)