Publication Date:
2017-04-04
Description:
Long-Period (LP) and Very-Long-Period (VLP) signals are themost characteristic seismic signature
of volcano dynamics, and provide important information about the physical processes
occurring in magmatic and hydrothermal systems. These events are usually characterized
by sharp spectral peaks, which may span several frequency decades, by emergent onsets,
and by a lack of clear S-wave arrivals. These two latter features make both signal detection
and location a challenging task. In this paper, we propose a processing procedure based on
Continuous Wavelet Transform of multichannel, broad-band data to simultaneously solve the
signal detection and location problems. Our method consists of two steps. First, we apply a
frequency-dependent threshold to the estimates of the array-averaged WCO in order to locate
the time-frequency regions spanned by coherent arrivals. For these data, we then use the
time-series of the complex wavelet coefficients for deriving the elements of the spatial Cross-
Spectral Matrix. From the eigenstructure of this matrix, we eventually estimate the kinematic
signals’ parameters using the MUltiple SIgnal Characterization (MUSIC) algorithm. The
whole procedure greatly facilitates the detection and location of weak, broad-band signals, in
turn avoiding the time-frequency resolution trade-off and frequency leakage effects which affect
conventional covariance estimates based uponWindowed Fourier Transform. The method
is applied to explosion signals recorded at Stromboli volcano by either a short-period, small
aperture antenna, or a large-aperture, broad-band network. The LP (0.2〈 T 〈2 s) components
of the explosive signals are analysed using data from the small-aperture array and under the
plane-wave assumption. In this manner, we obtain a precise time- and frequency-localization
of the directional properties for waves impinging at the array. We then extend the wavefield
decomposition method using a spherical wave front model, and analyse the VLP components
(T 〉 2 s) of the explosion recordings from the broad-band network. Source locations obtained
this way are fully compatible with those retrieved from application of more traditional (and
computationally expensive) time-domain techniques, such as the Radial Semblance method.
Description:
Published
Description:
435 - 450
Description:
3.1. Fisica dei terremoti
Description:
JCR Journal
Description:
reserved
Keywords:
Array techniques
;
Wavelet analysis
;
04. Solid Earth::04.06. Seismology::04.06.09. Waves and wave analysis
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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