Correlation between two arrays

Rhie and Romanowicz (2004) showed that there is a very good correlation between the variations in maximum stack amplitudes for two regional arrays at Japan (F-net) and California (BDSN) with common maximum amplitude on day 31 in 2000 at periods around 240 s. This correlation was explained by common sources generating long period surface wave energy over the ocean. Both seismic arrays detect maximum seismic energy arriving on day 31 and significant wave height measurements near the California and Japan coasts also show that wave heights were largest around day 31 in 2000. We took time windows from 30 to 35 days in 2000 to compare the variations in seismic amplitudes for the two arrays. Stack amplitude functions as a function of time and back-azimuth are computed for both arrays and moving averages with the duration of 6 hours and shift of 1 hour are taken. Stack amplitude functions are computed by correcting for dispersion based on PREM. Gaussian filters with center period of 150 s and 240 s had been taken before the dispersion correction and stacking. The overall trends for both arrays and both frequency bands are consistent, but if we look more carefully, some differences emerge. For example, it is clear that onsets of first maxima on day 31 for F-net and BDSN have a time difference of about 0.5 days, which is too large to be explained by seismic wave propagation from one common source under the assumption of minor arc propagation. This indicates that both arrays detect elastic energy arrivals coupled at different geographic regions.

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