Polarisation analysis of the independent components of low frequency events at Stromboli volcano (Eolian Islands, Italy)

Independent component analysis (ICA), applied on low-frequency (LF) events recorded at Stromboli volcano, reveals that these signals are composed of three independent components in three different frequency bands (approximately 0.8–1.2, 2.4–3.0, 3.2–4.5 Hz, respectively). The first two frequency ranges are mainly composed of body waves coming from a direction in a range of [−30°, 30°] around the crater area. This result is a clear indication that the entire signal, in these frequency bands, comes from the source area. In fact, any scattered wave should have different back azimuth propagation, due to the random distribution of scatterersʹ location. However, the last independent component is dominated by other kinds of waves, coming from many different directions.