LARGE APERTURE SEISMIC ARRAYS
Quarterly technical rept. no. 1, Jan-Mar 1966
GENERAL ATRONICS CORP PHILADELPHIA PA
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The work dealt with the effect of seismometer placement on array sidelobes, the performance to be expected with arrays using one bit signals from the seismometers, the coherence of signals, noise, and coda across LASA, P-coda correlation as a discriminant and the frequency dependence of attenuation in the earths upper mantle. A randomized array, as opposed to one with clustered elements, has shown sidelobes some 14 dB lower than those of the current LASA design. The one bit array DIMUS has shown a processing gain of 2 dB less than that for an analog array, as predicted by theory. The same array with the addition of a single analog channel offers good possibilities of proving as useful in identification as a conventional array. Main P, and noise correlations observed across LASA Montanna from LONGSHOT showed signal correlation to be high, 0.97, and noise quite low for spacings equal to those of the clusters. P- coda correlation decreased to a value near zero for seismometer spacings on the order of 150 km. Study of P-coda correlation coefficients for widely spaced seismometers fell into two distinct distributions with an equivalent SN of 16 dB. A method was developed for estimating the Q of the upper mantle using the P and pP phases of deep earthquakes. First test of the method indicate an average Q of approximately 200 for the upper 500 km of the mantle in the Fiji Islands Region.
- Seismic Detection and Detectors