Seismic monitoring of Campi Flegrei and Vesuvius by stand alone instruments

A seismic network of more than 20 broad band stations and two arrays of 10 short period stations each, all working in local acquisition mode, are used to improve the seismic monitoring of Campi Flegrei and Vesuvius for research purposes. Data provided by stand-alone instruments are characterized by high quality and very continuous data streams, therefore they are appropriate to detect and analyze any seismic signals possibly related with the volcanic activity. Array data are particularly useful to discover and analyze seismic events characterized by low amplitude, low signal to noise ratio and emergent onset, but whose signals are more coherent among the array stations than the background noise. Since the background seismic signal is very high at both volcanoes, particularly at Campi Flegrei, seismic arrays and dense station networks are necessary to discriminate volcanic events from the many transient signals produced by artificial sources. In Campi Flegrei area the analysis with array methods of data recorded by ARF array permitted the discovery of low amplitude volcanic tremor of hydrothermal origin occurred in January 2015, a seismic signal never observed before in the area. At Mt. Vesuvius the analysis of VAS array data has shown the occasional occurrence of short bursts of low amplitude volcanic tremor. Small low-frequency earthquakes have also been revealed in the two volcanic areas.