Additional cases are recognized at frequently active volcanoes including Popocateptl (2001) and Mauna Loa (1984. We present four case studies (Pinatubo, Soufriere Hills, Unzen, and Tacana') in which we demonstrate the above mentioned VT characteristics prior to eruptions. Using regional data recorded by NEIC, we recognized in near-real time that a huge distal VT swarm was occurring, deduced that a proportionately huge magmatic intrusion was taking place beneath the long dormant Sulu Range, New Britain Island, Papua New Guinea, that it was likely to lead to eruptive activity, and warned Rabaul Volcano Observatory days before a phreatic eruption occurred. This confirms the value of this technique for eruption forecasting. We also present a counter-example where we deduced that a VT swarm at Volcan Cosiguina, Nicaragua, indicated a small intrusion, insufficient to reach the surface and erupt. Finally, we discuss limitations of the method and propose a mechanism by which this distal VT seismicity is triggered by magmatic intrusion.

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[1] Regional network data reveal deep non-volcanic tremor occurs in five independent sections along the U.S. section of the Cascadia subduction zone with different recurrence intervals. Sizeable tremor episodes occur during periods with no measurable geodetic deformation as well as coincident with episodic slow slip events, and the displacement amplitudes of the tremor with and without geodetic deformation are similar. The tremor depths cover a wide range that does not coincide directly with the subducting slab interface. The tremor can migrate bidirectionally from the point of initiation, and more than one spatially distinct tremor source can be active at a given time. These results indicate that the tremor is not directly related to the slow slip event. Instead we suggest that the tremor is related to the presence and movement of fluids at depth, which can explain the locations and episodic occurrence as well as the seismic signal characteristics themselves; namely, the limited frequency content, small size, emergent onsets, and prolonged durations with and without geodetic deformation.