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

Self Cite

Abstract.We analyze time series of Strombolian volcanic tremor, focusing our attention on the frequency band [0.1-0.5] Hz (very long period (VLP) tremor). Although this frequency band is largely affected by noise, we evidence two significant components by using Independent Component Analysis with the frequencies, respectively, of ∼0.2 and ∼0.4 Hz. We show that these components display wavefield features similar to those of the high frequency Strombolian signals (>0.5 Hz). In fact, they are radially polarised and located within the crater area. This characterization is lost when an enhancement of energy appears. In this case, the presence of microseismic noise becomes relevant. Investigating the entire large data set available, we determine how microseismic noise influences the signals. We ascribe the microseismic noise source to Scirocco wind. Moreover, our analysis allows one to evidence that the Strombolian conduit vibrates like the asymmetric cavity associated with musical instruments generating self-sustained tones.

Section: Introductionmentioning

confidence: 99%

Statistical analysis of Stromboli VLP tremor in the band [0.1–0.5] Hz: some consequences for vibrating structures

Lauro

Martino

Falanga

et al. 2006

Self Cite

“…Consistently, decompositions in time-domain by high-order statistical methods of volcanic signals at high frequencies (> 0.5 Hz) have led to the extraction of few basic signals, modelled as the vibration modes of hydrothermal structures or magma-filled cavities (Acernese et al, 2004;De Lauro et al, 2009, 2012aDe Martino et al, 2011), whereas at low frequencies the superposition of volcanic tremor and microseismic noise has been detected (De Lauro et al, 2005Cabras et al, 2008).…”

Section: Published By Copernicus Publications On Behalf Of the Europementioning

confidence: 93%

Wavefield decomposition and phase space dynamics of the seismic noise at Volcàn de Colima, Mexico: evidence of a two-state source process

Palo

Cusano

2013

Abstract. We analyse the seismic noise recorded at the Colima Volcano (Mexico) in the period December 2005-May 2006 by four broadband three-component seismic stations. Specifically, we characterize the spectral content of the signal and follow its time evolution along all the data set. Moreover, we infer the properties of the attractor in the phase space by false nearest neighbours analysis and GrassbergerProcaccia algorithm, and adopt a time-domain decomposition method (independent component analysis) to find the basic constituents (independent components) of the system. Constraints on the seismic wavefield are inferred by the polarization analysis. We find two states of the background seismicity visible in different time-intervals that are Phase A and Phase B. Phase A has a spectrum with two peaks at 0.15 Hz and 0.3 Hz, with the latter dominating, an attractor of correlation dimension close to 3, three quasi-monochromatic independent components, and a relevant fraction of craterpointing polarization solutions in the near-field. In Phase B, the spectrum is preserved but with the highest peak at 0.15 Hz, the attractor has a correlation dimension close to 2, two independent components are extracted, and the polarization solutions are dominated by Rayleigh waves incoming from the southwest direction. We depict two sources acting on the background seismicity that are the microseismic noise loading on the Pacific coastline and a low-energy volcanic tremor. A change in the amplitude of the microseismic noise can induce the switching from a state of the system to the other.

“…Sometimes, it is interrupted by effusive phases and/or by big explosive The seismic wavefield at Stromboli has been extensively studied by using advanced signal processing techniques. In particular, Del Pezzo et al (1992), Chouet et al (1997), and Acernese et al (2003Acernese et al ( , 2004 studied the composition of the high-frequency wavefield (> 0.5Hz) associated with the explosion quakes. Chouet et al (2003) investigated the seismic wavefield associated with very long period events (VLP), and retrieved the equivalent elastic source mechanism which includes both moment tensor and single force components.…”

Section: Strombolimentioning

confidence: 99%

“…A first application of ICA to seismic signals was performed on explosion-quakes at Stromboli by Acernese et al (2003Acernese et al ( , 2004. After synchronizing the seismic traces at all the stations in order to have instantaneous mixtures (the conditions required by standard linear ICA), the authors preliminarily applied PCA to reveal the internal structure of the data and explain the variance in the data.…”

Section: Application Of Ica To Stromboli Seismic Signalsmentioning

confidence: 99%

“…As it can be seen, ICA decomposes the explosion-quake signals into three independent wave packets in the time domain, corresponding to well separated frequency bands ([0.8 − 1.5] Hz,[2 − 3.5] Hz, and [4 − 6] Hz). Each band is characterized (in terms of polarization analysis) by body waves with particle motion pointing toward the crater area, even though the highest frequency band is affected by incoherent and signal-generated (scattering) noise (Acernese et al, 2004).…”

Section: Application Of Ica To Stromboli Seismic Signalsmentioning

confidence: 99%

See 1 more Smart Citation

Self-sustained vibrations in volcanic areas extracted by Independent Component Analysis: a review and new results

Lauro

Martino

Falanga

et al. 2011

Self Cite

Abstract. We investigate the physical processes associated with volcanic tremor and explosions. A volcano is a complex system where a fluid source interacts with the solid edifice so generating seismic waves in a regime of low turbulence. Although the complex behavior escapes a simple universal description, the phases of activity generate stable (self-sustained) oscillations that can be described as a nonlinear dynamical system of low dimensionality. So, the system requires to be investigated with non-linear methods able to individuate, decompose, and extract the main characteristics of the phenomenon. Independent Component Analysis (ICA), an entropy-based technique is a good candidate for this purpose. Here, we review the results of ICA applied to seismic signals acquired in some volcanic areas. We emphasize analogies and differences among the self-oscillations individuated in three cases: Stromboli (Italy), Erebus (Antarctica) and Volcán de Colima (Mexico). The waveforms of the extracted independent components are specific for each volcano, whereas the similarity can be ascribed to a very general common source mechanism involving the interaction between gas/magma flow and solid structures (the volcanic edifice). Indeed, chocking phenomena or inhomogeneities in the volcanic cavity can play the same role in generating selfoscillations as the languid and the reed do in musical instruments. The understanding of these background oscillations is relevant not only for explaining the volcanic source process and to make a forecast into the future, but sheds light on the physics of complex systems developing low turbulence.