Triggering and runaway processes of catastrophic Tsaoling landslide induced by the 1999 Taiwan Chi-Chi earthquake, as revealed by high-velocity friction experiments

Abstract

Pliocene sedimentary rocks of about 130 Mm 3 in volume slid along bedding planes dipping by 14°, with an average speed of about 35 m/s, during the Tsaoling landslide. We conducted friction experiments to reproduce the initiation processes of this landslide, by idealizing landslide movements during the earthquake as accelerating/decelerating motion. Experiments were done on shale from the field, at 3 MPa normal stress corresponding to the overburden pressure. Results indicate that the accelerating/decelerating motion causes weakening and strengthening at each oscillation cycle and results in overall slip weakening which can be approximated as an exponential slip weakening. Behaviors during oscillatory slip are fairly similar to those during sliding at constant slip rates. Newmark analysis with measured frictional properties reveals that the landslide can be triggered with wet gouge properties, but the landslide motion stops with parameters for dry shale gouge. Delayed initiation of the landslide is consistent with a survivor's witness.

Initiation, movement, and run-out of the giant Tsaoling landslide — What can we learn from a simple rigid block model and a velocity–displacement dependent friction law?

“…As mentioned previously, the friction coefficient decreased from a peak value to a steady-state value with increasing displacement in the slip-weakening regime. The steady-state friction coefficients (μ ss ; red circles with crosses) decreased from approximately 0.27 to 0.05 with increasing velocity (Figure 8), which has been observed in numerous studies of high-velocity rotary shear tests (Miyamoto et al, 2009;Togo et al, 2014). The slipweakening distances (D c ) for our data range from 2.94 to 8.55 m with an average value of 4.90 m (Table 1).…”

“…Continuous U layers are absent when the shear velocity was less than 0.22 m/s (slip-strengthening regime). The U layer can be observed at a slip velocity of 0.1 m/s (Figure 13a Two datasets of rotary shear tests using dry and wet samples from the Tsaoling landslide site have been reported (Miyamoto et al, 2009;Togo et al, 2014). Togo et al (2014) documented the friction coefficients of dry shale powders of samples from the lower Cholan Formation near the slide plane (squares in Figure 14), and Miyamoto et al (2009) reported friction coefficients of dry bedding-parallel fault gouges (triangles in Figure 14).…”

“…This paper attempts to combine laboratory studies on the high-velocity frictional properties of sliding surface and a Newmark analysis of landslide motion, for a realistic prediction of the Tsaoling landslide. This landslide is the largest and best-documented landslide among several large landslides triggering by the 1999 Taiwan Chi-Chi earthquake (M w = 7.6) with its volume of about 125 Mm 3 (Hung, 2000;Weissel and Stark, 2001;Hung et al, 2002;Chigira et al, 2003;Wang et al, 2003;Chen et al, 2004;Chang et al, 2005;Chen et al, 2005Chen et al, , 2006Kuo et al, 2009;Miyamoto et al, 2009;Tang et al, 2009;Chen, 2009, 2011;Chang et al, 2013;Kuo et al, 2013;Chen et al, 2014;Togo et al, 2014). In particular, a landslide mass of the Pliocene Cholan Formation (about 140 m in thickness) slid along very flat bedding planes within alternated fine sandstone and shale beds dipping by 14°on the southern slope of the Tsaoling Mountain, as we discuss Figs.…”

“…Recently, Togo et al (2014) performed oscillatory velocity experiments on dry and wet shale gouge from the Tsaoling landslide site, by idealizing the Tsaoling landslide motion during the Chi-Chi earthquake as repeated accelerating/decelerating motion with a frequency ranging from 0.3 to 1.2 Hz. They observed small weakening and strengthening in association of the accelerating/decelerating motion, while undergoing overall slip-weakening.…”

“…We use in this paper a more involved friction law, particularly by including the velocity dependence of the steady-state friction which can affect the high-velocity sliding portion of the Tsaoling landslide. We also compiled all existing friction data, including those by Togo et al (2014). After our initial manuscript was submitted, an interesting paper was published by Chen et al (2014) who conducted the Newmark analysis of the Tsaoling landslide by combining the results from traditional direct shear tests cited above and from high-velocity friction experiments by Miyamoto et al (2009).…”