SEISMIC WAVEFIELD ARRAY PROCESSING ANALYSIS USING WAVELET COHERENCE

San Francisco, California, USA

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