Double-array refraction microtremors

• We override limitations of the standard ReMi technique with an alternative approach.
• We test the robustness of the method using synthetic and real data.
• We test active data allowing a partial validation of the passive results.
• We propose an intermediate step towards the full complexity of beamforming analysis.

We present a critical analysis of the limitations of the standard ReMi technique, specifically in the case of directional sources, and we propose an alternative approach for the efficient acquisition and processing of passive surface wave data, that exploits a simple and yet effective field layout (two linear orthogonal arrays) and processing strategy. The motivations for using a 2D array for passive surface wave testing are reviewed, together with the limitations of the classical ReMi approach. Using synthetic and real data, the robustness of the method is shown, and the limitations of the simplified processing route are described. The possibility of acquiring active data on the same receiver spread allows a partial validation of the passive results, in terms of propagation direction, in addition to producing a broader band dispersion curve to be used in the inversion process. The proposed approach is an intermediate step towards the full complexity of beamforming analysis, that can be of simple use for practitioners and yet help avoid the most common and dangerous interpretation pitfalls inherent to linear array micro-tremor techniques.