Figure 2. The seismograms and spectra from the three IS stations recording the seismic precursor on the morning of October 7. The attack began at 06:30 local time. (a) Vertical component seismograms from AMZNI, YATR, and KZIT showing ground velocity as a function of local time on October 7. The grey rectangle indicates the portion of the pre-attack seismograms where strong correlated signals are observed on YATR and KZIT. Note that strong noise fluctuations begin at AMZNI around 05:10 (Figure 3a), before the earliest time shown in this panel. (b-d) Three-component spectra recorded at AMZNI, YATR, and KZIT. The black curve is for the time window between 06:20 and 06:30 on October 7. The light-blue strip shows the median background noise level \(\pm1\) median standard deviation. The noise curve was computed from spectra recorded during Saturday mornings between 2021 and 2023.