From seismic network optimization to real-time diagnosis of magma migration

Triggering mechanism of a seismic swarm has to be identified with great confidence in real time. Crisis response will not be the same whether magma is involved or not. The method based on the Seismic Amplitude Ratio Analysis enables a rapid and unambiguous diagnosis to detect migrating micro-seismicity. Combined with other measurements, this migrating seismicity could be linked to complex motions of magma within the volcanic edifice. The beauty of this method lies in the fact that the ratio of seismic energy recorded at different stations is independent of the seismic energy radiated at the source. Drastic changes in attenuation are unlikely to occur at the time scale of magma intrusion, therefore temporal evolutions in the measured ratio have to be explained by a change in the source location. Based on a simple assumption this technique can be used to assess the potential of existing monitoring seismic network to detect migrating events in real-time. It can also be used to design monitoring seismic network based on the available number of sensors as well as from field constraints. Network capability also depends on the noise level at each station, therefore this noise is used to define the magnitude threshold that can be detected as a function of the distance.