Characterization of the seismic dynamical state through joint analysis of earthquakes and seismic noise: the example of Ischia Volcanic Island (Italy)
2020
Abstract. This work is devoted to the study of both earthquakes and background seismic
noise at Ischia Island (Italy) recorded pre and post the Md 4.0 earthquake
occurred on 21 August 2017 (18:57 UTC). We compare and characterize noise
and earthquakes in terms of Independent Component Analysis, energy and
polarization properties. The earthquakes' waveforms and the background noise
are decomposed into a few independent components with two main common
signals peaked around 1–2 and 3–4 Hz , respectively. A slight increase of
the energy of the background seismic noise is observed comparing samples
recorded in 2016 and 2017, whereas no variations are detected in 2017 pre
and post the main earthquake. The polarization analysis, performed in the
frequency bands individuated by Independent Component Analysis and applied
to the background seismic noise, indicates a shallow propagation and the
azimuthal pattern is mainly controlled by the local structural features.
These results suggest that noise and earthquakes are ascribable to a common
phenomenon of fluid-solid interaction in the hydrothermal system of Ischia
Island.
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