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GEOREF RECORD

Physical properties of deep crustal reflectors in Southern California from multioffset amplitude analysis

John N. Louie
Physical properties of deep crustal reflectors in Southern California from multioffset amplitude analysis
Geophysics (June 1990) 55 (6): 670-681

Abstract

Analysis of reflection waveforms before stack can constrain the physical properties of reflectors in the deep crust. To simplify this analysis, recorded amplitudes are assumed to be reflections from weak elastic heterogeneities. With these assumptions, trends in reflection amplitudes with offset may indicate whether the signs of a reflector's density and rigidity contrast agree with or oppose the sign of its Lame's parameter contrast. The slope of the trend indicates the degree of Poisson's ratio contrast. No attempt is made to invert for the individual modulus or density contrasts. By examining only gross amplitude-versus-offset (AVO) trends, deep reflections constrain some crustal properties.Two seismic reflection surveys in the Mojave Desert recorded deep reflections that show amplitude changes with offset. Both the 1985 Calcrust Ward Valley survey in the eastern Mojave and the 87 km COCORP Mojave line 3 in the western Mojave incorporate long offsets of 10 km or more. Prestack traces are equalized using a quantile technique assuming a constant noise level at large time, then corrected for spherical divergence. Gross AVO trends that are summarized for each survey in amplitude trend stacks suggest that the strongest reflectors in the middle and deep crust represent Poisson's ratio contrasts of at least 10 percent. In the eastern Mojave, a transition to a basal-crustal zone, at approximately 23 km depth, may include an increase in Poisson's ratio with depth. Poisson's ratio may also increase at the Moho.


ISSN: 0016-8033
EISSN: 1942-2156
Coden: GPYSA7
Serial Title: Geophysics
Serial Volume: 55
Serial Issue: 6
Title: Physical properties of deep crustal reflectors in Southern California from multioffset amplitude analysis
Author(s): Louie, John N.
Affiliation: Pa. State Univ., Dep. Geosci., University Park, PA, United States
Pages: 670-681
Published: 199006
Text Language: English
Publisher: Society of Exploration Geophysicists, Tulsa, OK, United States
References: 27
Accession Number: 1990-035245
Categories: Solid-earth geophysics
Document Type: Serial
Bibliographic Level: Analytic
Annotation: Presented at the 56th ann. int. meet., Soc. Explor. Geophys.
Illustration Description: illus. incl. 1 table
N33°30'00" - N37°15'00", W118°00'00" - W112°30'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data supplied by Society of Exploration Geophysicists, Tulsa, OK, United States
Update Code: 1990
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