LONG-PERIOD SUMMATION PROCESSING - LARGE-ARRAY SIGNAL AND NOISE ANALYSIS

Abstract : Ten LASA long-period event records were demultiplexed and displayed for use in a signal extraction study. In addition, time-shift-and-sum outputs of the vertical, horizontal inline, and horizontal transverse elements were formed for several of the events. Approximate Rayleigh wave velocities were used for the vertical and inline sums, while the transverse elements were beamed with Love wave energy. Examination of the traces and beamsteer outputs lead to the following conclusions. A given event is perceived with considerable dissimilarity by the various LASA sensors. At a given location, however, the Rayleigh-wave vertical and horizontal components have similar waveforms and are about equal in amplitude. The ratio of Love- to Rayleigh-wave peak amplitude varies from about 0.5 to 2.0. Despite the waveform dissimilarity, beams formed with elements from the A0 through the D-ring show less than 1-db signal attenuation for Rayleigh waves. Rayleigh wave beams using the entire array show 1- to 3-db signal attenuation.