Three-Component Seismic Array Analysis in the Discrete Wavelet Domain

The purpose of this PhD thesis was the development of an innovative methodology for the seismic array data analysis, named DWT-MuSiC (Discrete Wavelet Transform -Multiple Signals Classification). DWT-MuSiC is a new proposed method intended to be able to perform near-real time analysis relating to the detection of different seismic wave field and their characterization, starting from raw seismic array data. The innovative point of DWT-MuSiC is that it is thought to combine the resolution of the MuSiC (Multiple Signals Classification) algorithm, methodology used for frequency estimation and source location, proposed by Schmidt (1986), and the potentialities of the discrete wavelet domain analysis. The DWT-MuSiC, in fact other than detecting the presence of different wavefronts, provides both their direction of arrival and apparent speed of advancement, returning even information about the polarization of each identified phases, preserving furthermore spatial and frequency information of the original signals. The synthetic tests performed with the DWT-MuSiC analysis have shown the ability of the algorithm to detect wake signals also in presence of a low signal to noise ratio. The method returned correct output also in those cases where the analysis is performed on multiple seismic phases that overlap in terms of impinging time or/and frequency content of the signals themselves. The comparison between other methodology like the beamforming and MuSiC applied in the Fourier domain, shown how the information returned by the DWT-MuSiC was much more complete. The use of discrete wavelets and the optimization algorithm implemented in the analysis permit moreover to save computational time analyzing only the important data, allowing the recovery of hidden information when more than one wavefronts overlap. The application to real case on data collected at Mount Vesuvius (Italy) and at Krafka caldera (Island) were important to test the applicability of the methodology in different contests.