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Increase of shear wave velocity before the 1998 eruption of Merapi volcano (Indonesia)

We infer temporal changes in the elastic properties of the edifice of Merapi volcano (Java, Indonesia) before its eruption in 1998 by analyzing multiply scattered elastic waves excited by a repeatable controlled seismic source. A pre‐eruptive increase of shear wave velocity, which correlates well with pre‐eruptive seismicity and dome‐growth is revealed. The method can be used as a “pressure‐gauge” for pressure changes inside of volcanoes, because increasing pressures in rocks are known to cause proportionally increasing elastic wave velocities.