A STUDY OF THE CAPABILITY OF LASA TO AID THE INDENTIFICATION OF A SEISMIC SOURCE
MASSACHUSETTS INST OF TECH LEXINGTON LINCOLN LAB
Pagination or Media Count:
Several studies have been performed to investigate the ability of a LASA or a network of LASAs to aid in discriminating between explosions and natural earthquakes from observations of the seismic waves they generate. The major effort has been an attempt to relate the ability to observe the pP phase, first motion, and complexity of an event to the well-documented ability of LASA to improve signal-to-noise ratio. The results indicate that the ability to see first motion varies directly with SNR, but that the ability to identify pP is apparently improved more than the SNR gain would indicate, probably due to the ability of a large array to measure velocity directly. In this study, no quantitative gauge for defining the correct value of complexity has been found therefore, we made no attempt to estimate a level of improvement for determination of complexity. It appears that complexity can vary widely between different subarrays and, of course, combining subarrays tends to smooth out the variations. Two experiments designed to take advantage of the high SNR gains available at the lower frequency end of the short-period band 0.1 - 1.0 cps are in progress. One of these, an attempt to observe S-wave energy on small events, has been hampered by an unexpected and, as yet unexplained high level of signal distortion. The other study, designed to investigate the pattern of P- wave spectra in the 0.1 to 1.0 cps region, has indicated that the energy in this band may be lower for explosions than for earthquakes, but it is too early in the study to state quantitative results.
- Seismic Detection and Detectors