Fig. 10

a Vertical displacement \(\Delta z\) versus time (5-point running averaged) of the \(H \simeq 20\) cm, \(L = 13.5\) cm cliffs. Hydraulic head \(h_{\mathrm{w}}\) varies in the range of \(h_{\mathrm{w}} = 1.8\)–15 cm (numbers annotated). Solid (broken) lines indicate the cases in which the slides were triggered (not triggered). \(\bigcirc\) indicates the \(\Delta z\) at the \(T_\mathrm{slide}\), which is defined from the threshold velocity \(v_0\) (see b). b Vertical velocity \(v_{\mathrm{z}}\) versus time (5-point running averaged) calculated from a using the runs in which a slide was triggered. \(\bigcirc\) indicates the \(T_{\mathrm{slide}}\) defined at the threshold \(v_0 = 0.1\) mm/s. c \(T_{\mathrm{seep}}\) (\(\bigtriangleup\)) and \(T_{\mathrm{slide}}\) (\(\bigcirc\)) versus \(h_{\mathrm{w}}\) of the \(H \simeq 20\) cm cliffs (see Additional file 4: Fig. S5 for a semi-log version). The upper horizontal axis is in the \(h_{\mathrm{w}} / H\) scale. Solid and broken curves indicate the \(T_{\mathrm{seep}}\) calculated by solving Eq. (10) using 2 permeability (k) values: \(k_1 = 5.0 \times 10^{-11}\) \(\text{ m}^2\) and \(k_2 = 1.8 \times 10^{-11}\) \(\text{ m}^2\). d \(T_{\mathrm{seep}}\), \(T_{\mathrm{slide}}\) versus H for a constant \(h_{\mathrm{w}} \simeq 2\) cm (see Additional file 4: Fig. S6 for the \(\Delta z\) vs. time plot). There are no measurements of \(T_{\mathrm{slide}}\) for 4 runs (slide not triggered (3 runs), sensor data acquisition stopped (1 run); see Table 2 legend). The 2 horizontal lines indicate the \(T_\mathrm{seep}\) calculated for \(h_{\mathrm{w}} = 2\) cm using the same \(k_1\) and \(k_2\) values used in c