SEISMIC WAVEFIELD ARRAY PROCESSING ANALYSIS USING WAVELET COHERENCE

Abstract

Volcanic signals are one of the most difficult subject of study for seismologists. The lack of clear body-wave phase arrivals and the rapid loss of signal coherence with distance make generally impossible application of traditional location techniques based on travel times inversion. Overthe past ten years,however,the wides pread application of multichannel techniques hasal lowed forrobust and reliable locations of these signals over abroad range of frequencies. Consequent to the largely increased computing capabilities, array processing in Volcano Observatories is now developing to ward thereal-time detection and tracking of volcanic sources. However,the energy of volcanic signals may spread over abroad frequency interval(Fig.1).The successful detection and measurement of these signals requirest herefore subsequent band-pass filtering operations, and exact tayloring of the time window lengthsto the central frequency of each filter. Exploting the localisation properties of Continuos Wavelet Transforms (CWT)in the time and frequency /scaledomains,in this workweuse multichannel Wavelet Coherence (WCO)toperform signal detection from local correlation information. For the time/scale regions of high multichannel coherence, wethenextend the MUltiple Signal Classification (MUSIC) methodto the spatial covariance matrice sobtained from the complex-valued wavele tcoefficient timeseries