Coupled-mode separation of multiply scattered wavefield components in two-dimensional waveguides

Area of Science:

• Geophysics
• Wave Propagation
• Computational Seismology

Background:

• Wave propagation in heterogeneous media is crucial for understanding seismic wave phenomena.
• Local geological anomalies, such as alluvial valleys, can significantly amplify seismic ground motion.
• Accurate modeling of multiple scattering is essential for seismic hazard assessment.

Purpose of the Study:

• To develop a mathematically exact partial-wave decomposition for analyzing wavefield behavior in waveguides.
• To assess multiple scattering effects caused by horizontally displaced medium anomalies.
• To provide a method applicable to seismic wave propagation and ground motion studies.

Main Methods:

• Partial-wave decomposition of the wavefield.
• Discrete coupled-mode theory and reflection/transmission matrices.
• Avoidance of high-frequency ray approximations, ensuring mathematical exactness.
• Application of global optimization for artificial medium termination.
• Derivation of horizontal source arrays for incident plane waves.

Main Results:

• A novel, mathematically exact method for analyzing wave scattering in horizontally invariant waveguides.
• The method accurately models multiple scattering without relying on high-frequency approximations.
• Demonstration of applicability to seismic wave amplification by geological anomalies like alluvial valleys.
• Extension of Fourier-transform relations involving Bessel functions.

Conclusions:

• The presented partial-wave decomposition offers a robust and accurate tool for studying wave propagation and scattering in complex media.
• This method provides a valuable alternative to purely numerical techniques for analyzing 2D anomaly shapes.
• The findings have direct implications for understanding and predicting seismic ground motion amplification.