with the speed of sound, as well as the plume exit velocity of Eyjafjallajökull
volcano calculated by Ripepe et. al., 2013, indicating that the first tremor that can be seen is
actually caused by an acoustic wave travelling through the
air.
16
Figure 9. Seismic network maintained by the IMO as of February 26, 2000. The location of
Hekla is marked by a red star. The four stations to the WSW plotted
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