Broadband Signal Enhancement of Seismic Array Data: Application to Long-Period Surface Waves & High Frequency Wavefields
Final rept. 1 Nov 93-31 Oct 97
SCRIPPS INSTITUTION OF OCEANOGRAPHY LA JOLLA CA INST OF GEOPHYSICS AND PLANETARY PHYSICS
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We demonstrate the use of dual-frequency coherence in detecting and characterizing seismic surface waves. Using a multitaper method, we calculate the coherence between different frequencies of one or multiple signals. We test the algorithm both on a variety of synthetic signals and on broad-band seismic data. Dispersive waves such as seismic surface waves are easily identified and we show that the method is robust in the presence of noise. Phase relationships between different frequencies can be extracted, allowing reconstruction of the original phase function. Dual-frequency coherence is useful in identifying overtones and frequency shifts between signals, features which are undetectable by standard coherence measures. We construct a filter to extract only the coherent frequencies from a waveform and show that it significantly increases the signal-noise-ratio for dispersive waveforms.