Seismic polarization of LP and VT earthquakes at Campi Flegrei by ICAP

Abstract

We show how to obtain a clear separation of seismic phases in volcanic environments. Specifically we investigated the Long-Period (LP) and Volcano Tectonic (VT) seismic signals recorded at Campi Flegrei Caldera (Italy). We adopt an innovative Independent Component Analysis (ICA) algorithm for mixed seismic series adapted and improved to give automatic procedures for detecting seismic events often buried in the high-level ambient noise. We reconstruct the radiation patterns of the extracted LP events in order to link the individuated signals directly to the sources. We take advantage from ICA that provides basic signals along the three directions of motion so that a direct polarization analysis can be performed with no other filtering procedures. We show that the extracted signals are mainly composed of P waves with radial polarization pointing to the seismic source of the main LP swarm, i.e. a small area in the Solfatara, also in the case of the small-events, that both precede and follow the main activity. From a dynamical point of view, they can be described by two degrees of freedom, indicating a low-level of complexity associated with the vibrations from a superficial hydrothermal system. Additionally, we also focus on VTs, obtaining a clear separation of P and S phases: the technique not only allows the identification of the interval time P-S giving the timing of both phases but also provides the independent waveforms of the P and S. The proposed approach (ICAP) can represent an useful tool to obtain the polarization properties on seismic signals both originated from the interaction fluid-solid or by the rock fracturing.