Detection of Velocity Variations in Explosive Volcanoes Using Ambient Noise Correlation: The Ubinas Volcano, Peru

Abstract:

In this work, we calculate seismic velocity variations and decoherence of the wavefield by ambient noise correlation during the 2014 eruptive sequence of Ubinas volcano, Peru. We use both cross-correlation between pairs of stations and auto-correlation between vertical and horizontal components of single stations. The major explosions that occurred from April 13 to 19 were preceded by clear velocity decrease estimated from cross-correlation and auto-correlation. The MW=8.2 Iquique earthquake produced also a co-seismic velocity drop on April 1, 2014. This later variation was detected using higher frequency range than for the estimation of the velocity change associated to the volcanic activity. We locate in the horizontal plane the velocity perturbation and the structural change related with decoherence between several time periods in the coda. During the main phase of eruptive activity, the velocity decrease originated in the whole edifice while the structural perturbation is concentrated on the south flank of the volcano, a zone that corresponds to an old collapse. We suggest that the observed velocity variations are due to the dilatation of the edifice and to microfracturation induced by magma pressurization. The effect of the structural change may be locally enhanced by a possible zone of material weakness in the southern sector due to the old collapse. The approaches used in this study provide new types of precursor that can help the forecast of eruptions on explosive volcanoes.