Quantifying the kinematic signature of teh vertical buckling instability and the subsequent b/p formation. Left panel: temporal evolution of vertical-to-radial velocity dispersion (σ_zz/σ_RR), calculated within the b/p extent (R_b/p), (σ_zz/σ_RR)²(t; R ≤ R_b/p), for thin (in blue), thick (in red), and total (thin+thick) disc (in black) particles, for model rthickE0.5. Right panel: temporal evolution of meridional tilt angle (Θ_tilt), calculated within R_b/p using Eq. (7), for thin (in blue), thick (in red), and total (thin+thick) disc (in black) particles, for model rthickE0.5. The vertical maroon dotted line denotes the onset of bar formation (τ_bar), while the vertical magenta dotted line denotes the onset of buckling instability (τ_buck; for details, see text).