Amplitude Pattern Effects on NORSAR P-wave Detectability

Abstract : A detailed mapping of NORSAR P-wave amplitude anomalies as a function of the array's beam locations has been performed. For several regions there is as much as 20 dB amplitude variations across the array. There is, however, usually less than 0.3 dB to gain in signal-to-noise ratio by excluding one or more of the NORSAR subarrays. Moreover, one will have to use very small regions, i.e., one set of weights for each of the Detection Processor beams. This because the amplitude pattern, although stable for events coming in on the same beam, may change very drastically from one beam location to the nearest one.