B3AM: A beamforming toolbox for three-component ambient seismic noise analysis

Abstract

We introduce the MATLAB toolbox B3AM for beamforming of three-component ambient noise array data. We explain the theory behind three-component beamforming and polarisation analysis in particular, provide an overview of the workflow, and discuss the output using a worked example. The strength of the presented code package is the analysis of multiple beam response maps from multiple time windows. Hence, it provides statistical information about the ambient noise wavefield recorded over a period of time, such as the ratio of surface to body waves, average dispersion velocities, or dominant propagation direction. It can be used to validate assumptions made about the ambient noise wavefield in a particular location, helping to interpret results from other techniques, such as the analysis of horizontal-to-vertical spectral ratios or ambient noise interferometry, and enabling more precise monitoring of specific wavefield components. While designed initially with seismic networks in mind, B3AM is applicable over a wide range of frequencies and array sizes and can thus be adapted also for laboratory settings or civil engineering applications.

Keywords

• data processing
• Ambient seismic noise
• beamforming
• Matlab
• Python
• seismic anisotropy