Accession Number : ADA184203

Title :   Teleseismic Waveform Modeling Incorporating the Effects of Known Three-Dimensional Structure Beneath the Nevada Test Site.

Descriptive Note : Final rept. 4 Feb 85-3 Feb 87,

Corporate Author : MASSACHUSETTS INST OF TECH CAMBRIDGE EARTH RESOURCES LAB

Personal Author(s) : Cormier,Vernon F

PDF Url : ADA184203

Report Date : 08 Jun 1987

Pagination or Media Count : 106

Abstract : The pattern of teleseismic amplitudes from underground nuclear tests has been found to have strong variations as a function of location within a test site. Forward modeling of body waves in known three-dimensional structures beneath seismic sources is used to investigate the effects of such structures on teleseismic amplitudes and to determine the structural resolution necessary to formulate amplitude corrections for variations in source site and recording networks. Three-dimensional structures having scale lengths of 20 to 50 km down to 100 km depth with several per cent fluctuation in P and S velocity are shown to produce a factor of three fluctuation in the amplitude of teleseismic body waves. The associated travel time fluctuations introduced by the three-dimensional structures are weak, being on the order of several tenths of a second, and exhibit only a weak regional correlation with amplitude fluctuations. A known structure beneath Pahute Mesa, Nevada Test Site may be used to formulate amplitude corrections that may reduce the variance in a yield estimate by 25 per cent. Magnitudes based on measurements of coda amplitudes or integrated energy flux in a time window following and including the direct P phase can reduct the fluctuations within of observations by a seismic network, but will only partially successful in reducing the effects of near-source structure.

Descriptors :   *SEISMIC WAVES, *ROCK MECHANICS, *NUCLEAR EXPLOSION TESTING, *UNDERGROUND EXPLOSIONS, AMPLITUDE, CORRECTIONS, VARIATIONS, ENERGY, FLUX(RATE), INTEGRATED SYSTEMS, LONG RANGE(DISTANCE), PATTERNS, PHASE, FORWARD AREAS, MODELS, TEST FACILITIES, NETWORKS, RECORDING SYSTEMS, VELOCITY, SEISMOLOGY, SITES, SOURCES, STRUCTURES, MODELS, WAVEFORMS, THREE DIMENSIONAL, TRAVEL TIME, CORRELATION, LOW STRENGTH, LENGTH, SCALE, SEISMOLOGY, SOURCES, RESOLUTION, STRUCTURAL PROPERTIES, TEST FACILITIES

Subject Categories : Seismology
      Seismic Detection and Detectors

Distribution Statement : APPROVED FOR PUBLIC RELEASE