Detection of volcanic earthquakes and tremor in Campi Flegrei

The Campi Flegrei Caldera is an active volcanic area located in southern Italy and characterized by very high volcanic risk. The seismic activity of the area is monitored by a dense multi-parametric network including a seismic array (ARF) located in the central part of the caldera. Analyses with array techniques carried out on continuous data provided by ARF array allows for the detection of coherent signals possibly related to the volcanic activity. The most interesting seismic event occurred on January 30, 2015, and was classified as volcanic tremor of hydrothermal origin. This tremor is characterized by low signal-to-noise ratio, a well defined backazimuth pointing to the SE and apparent velocity of about 0.7 s/km, while the most of energy is observed in the 1-3 Hz frequency band. The strongest bursts of tremor are recognized at many stations of the local network, and the relative arrival time joint with the results of array analysis permits a raw location of the epicentral area SW of Solfatara crater. Many other signals characterized by high coherence among the array stations were found, but often their classification is difficult. Uncertain classification remains for many events, particularly those located at sea near the shore.