Detection of Seismic Signals from Background Noise in the Area of Campi Flegrei: Limits of the Present Seismic Monitoring

Abstract

Online Material: Table of seismic station location and seismometer type. Seismic monitoring of active volcanoes is necessary for detecting changes in background volcano dynamics to put in evidence possible precursors of an imminent eruption. Unfortunately, there is no clear relationship between the energy of precursory signals and the strength of subsequent volcanic activity. For example, swarms of small and shallow volcano‐tectonic (VT) or long‐period (LP) quakes (for the usual current classification, see Chouet, 2003) or volcanic tremor episodes may be the only seismic precursor of important phreatic activity (see Barberi et al. , 1992; Nakada and Shimizu, 1999). In case of high noise level, these signals may be thus partly or totally masked, making impossible the detection of these precursors. Accurate monitoring procedures should take into account the minimum magnitude detection threshold characteristics of the operating seismic network. In other words, the minimum event energy that can be detected in a given area should be considered as one of the important parameters to measure to test the real capacity of detecting a warning. This is particularly crucial in risky areas, such as Campi Flegrei, which is so densely populated to be considered as one of the most dangerous volcanoes in the world. Campi Flegrei is characterized by very high background seismic noise, and the knowledge of the minimum detectable magnitude is therefore crucial in this area (Petrosino et al. , 2008). For this reason, one of the purposes of the recent research project named UNREST, funded by the Civil Defense of Italy, was to achieve this objective and give useful constraints to the future improvements of the permanent seismic network, which operates in the Campi Flegrei area for volcano monitoring purposes. In the present paper, we will describe the field survey (Fig. 1) and the data analysis of an experiment carried …