Energy partitioning into the strain tensor components for diffuse elastic waves in three-dimensional homogeneous...

Area of Science:

• Geophysics
• Seismology
• Optical Fiber Sensing

Background:

• Distributed Acoustic Sensing (DAS) enables dense axial strain measurements along optical fibers.
• The partitioning of seismic wave energy into measured strain components remains poorly understood.
• Existing research focuses on energy partitioning into displacement components.

Purpose of the Study:

• To formulate energy partitioning into different strain tensor components for diffuse waves.
• To investigate the depth-dependent contributions of body and surface waves to strain components.
• To provide a framework for quantitative interpretation of DAS strain seismograms.

Main Methods:

• Developed a theoretical model for energy partitioning into six independent strain components.
• Analyzed diffuse wave propagation in a 3D homogeneous isotropic half-space.
• Examined the influence of depth on wave contributions to strain components.

Main Results:

• Surface DAS measurements (horizontal strains) are dominated by shear horizontal-waves and Rayleigh waves.
• Borehole DAS measurements (vertical strain) are initially dominated by Rayleigh waves.
• Rayleigh wave contribution to vertical strain decays rapidly with depth, with shear vertical-wave contribution persisting.

Conclusions:

• The study provides a theoretical basis for understanding seismic wave energy partitioning in DAS measurements.
• Findings clarify the wavefield composition of measured strains at different depths and locations.
• This work facilitates quantitative interpretation of DAS strain data, particularly the late coda.