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Fig. 2 | Earth, Planets and Space

Fig. 2

From: An experimental approach to unravel 2D ground resonances: application to an alluvial-sedimentary basin

Fig. 2

Assessment of the principal axes of motion of a hypothetical valley with axis oriented 40°N. a Observed resonance peaks along instrumental x and y components (grey and black, respectively, with the peaks marked by a black dot and a grey triangle) corresponding to the acquisition configuration drawn on the right (with y component parallel to geographic North). These correspond to the projections of the principal axes of motion of the valley. b x and y spectral components of signal rotated counterclockwise around the vertical axis between 0 and 80 degrees, with 10 degrees resolution. The rotation determines that the peaks along the x direction move within the area bounded by grey curves with the peaks marked by the grey triangles, while the y spectral peaks move within the area bounded by black curves with the peaks marked by the black dots. The thick blue line highlights the peak with lowest frequency and highest amplitude, i.e., the fundamental vibration mode along the longitudinal direction (blue direction on the polar plot), at the rotation angle \({\theta }_{s}\). c L0 and T0 modes along the real longitudinal and transverse direction of the valley

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