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Wave-equation Rayleigh-wave dispersion inversion using fundamental and higher modes

Zhendong Zhang and Tariq Alkhalifah
Wave-equation Rayleigh-wave dispersion inversion using fundamental and higher modes
Geophysics (July 2019) 84 (4): EN57-EN65

Abstract

Recorded surface waves often provide reasonable estimates of the S-wave velocity in the near surface. However, existing algorithms are mainly based on the 1D layered model assumption and require picking the dispersion curves either automatically or manually. We have developed a wave-equation-based inversion algorithm that inverts for S-wave velocities using fundamental and higher mode Rayleigh waves without picking an explicit dispersion curve. Our method aims to maximize the similarity of the phase velocity spectrum (f-v) of the observed and predicted surface waves with all Rayleigh-wave modes (if they exist) included in the inversion. The f-v spectrum is calculated using the linear Radon transform applied to a local similarity-based objective function; thus, we do not need to pick velocities in spectrum plots. As a result, the best match between the predicted and observed f-v spectrum provides the optimal estimation of the S-wave velocity. We derive S-wave velocity updates using the adjoint-state method and solve the optimization problem using a limited-memory Broyden-Fletcher-Goldfarb-Shanno algorithm. Our method excels in cases in which the S-wave velocity has vertical reversals and lateral variations because we used all-modes dispersion, and it can suppress the local minimum problem often associated with full-waveform inversion applications. Synthetic and field examples are used to verify the effectiveness of our method.


ISSN: 0016-8033
EISSN: 1942-2156
Coden: GPYSA7
Serial Title: Geophysics
Serial Volume: 84
Serial Issue: 4
Title: Wave-equation Rayleigh-wave dispersion inversion using fundamental and higher modes
Affiliation: King Abdullah University of Science and Technology, Department of Physical Science and Engineering, Thuwal, Saudi Arabia
Pages: EN57-EN65
Published: 201907
Text Language: English
Publisher: Society of Exploration Geophysicists, Tulsa, OK, United States
References: 35
Accession Number: 2020-013223
Categories: Applied geophysics
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sketch map
N17°00'00" - N32°30'00", E34°45'00" - E57°00'00"
N10°00'00" - N30°00'00", E34°00'00" - E43°00'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2020, American Geosciences Institute.
Update Code: 2020
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