Jia-Jyun Dong

The influence of surface ruptures on building damage in the 1999 Chi-Chi earthquake: a case study in Fengyuan City

Abstract In addition to the main surface rupture along the Chelungpu fault associated with the 1999 Chi-Chi, Taiwan earthquake, numerous secondary or branch ruptures on hangingwall were also observed. These secondary surface ruptures are parallel or sub-parallel to the main rupture within a distance of a few meters to 1–2 km. The rupture length of these secondary ruptures varies from a few tens of meters up to 5 km. The surface deformation resulted in serious damages of buildings. The present work studied the features of surface deformation on the hangingwall around the Chung-Cheng Park, Fengyuan, Taichung. Three distinct surface ruptures, minor ruptures and tension cracks were observed in this area. The observed distribution and types of building damage on the hangingwall are demonstrated. Due to the difference in geological condition and complex pattern of surface deformation, the resulted building damages on the hangingwall vary. A series of site investigation including field survey, drilling, seismic prospecting, P–S logging tests and laboratory tests were carried out in the interested area. A geological structure model was proposed on the basis of the results of site investigation. Numerical simulation was carried out to model the surface deformation as well as subsurface potential damage zone of an active fault. It reasonably explains the observed pattern of surface deformation and indicates that the surface deformation zone during a catastrophic earthquake is predictable.

New entropy-based method for variables selection and its application to the debris-flow hazard assessment

We propose a new data analyzing scheme, the method of minimum entropy analysis (MEA), in this paper. New MEA provides a quantitative criterion to select relevant variables for modeling the physical system interested. Such method can be easily extended to various geophysical/geological data analysis, where many relevant or irrelevant available measurements may obscure the understanding of the highly complicated physical system like the triggering of debris-flows. After demonstrating and testing the MEA method, we apply this method to a dataset of debris-flow occurrences in Taiwan and successfully find out three relevant variables, i.e. the hydrological form factor, numbers and areas of landslides, to the triggering of observed debris-flow events due to the 1996 Typhoon Herb.

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

Pliocene sedimentary rocks of about 130 Mm3 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 survivors witness.

Deriving landslide dam geometry from remote sensing images for the rapid assessment of critical parameters related to dam-breach hazards

Dam-breaches that cause outburst floods may induce downstream hazards. Because landslide dams can breach soon after they are formed, it is critical to assess the stability quickly to enable prompt action. However, dam geometry, an essential component of hazard evaluation, is not available in most cases. Our research proposes a procedure that utilizes post-landslide orthorectified remote sensing images and the pre-landslide Digital Terrain Model in the Geographic Information System to estimate the geometry of a particular dam. The procedure includes the following three modules: (1) the selection of the reference points on the dam and lake boundaries, (2) the interpolation of the dam-crest elevation, and (3) the estimation of dam-geometry parameters (i.e., the height, length, and width), the catchment area, the volumes of barrier lake and landslides dam. This procedure is demonstrated through a case study of the Namasha Landslide Dam in Taiwan. It was shown the dam-surface elevation estimated from the proposed procedure can approximate the elevation derived from profile leveling after the formation of the landslide dam. Thus, it is feasible to assess the critical parameters required for the landslide dam hazard assessment rapidly once the ortho-photo data are available. The proposed procedure is useful for quick and efficient decision making regarding hazard mitigation.

Velocity-Displacement Dependent Friction Coefficient and the Kinematics of Giant Landslide

Friction characteristics on the sliding surface of giant landslide is important for investigating the triggering, moving, and deposition. In this research, we incorporating a velocity-displacement dependent friction law into the Newmark method to predict the kinematics of a giant landslide. The parameters of the friction law are determined from the high velocity rotary shear experiments of shale and the fault gouge collected from the Tsaoling landslide site triggered by Chi–Chi earthquake in 1999. Based on the strong ground motion data and the account of a survivor, the proposed approach is validated. It is concluded that the Newmark method incorporating into a velocity-displacement dependent friction law can be used to precisely reproduce the detachment, rapid moving, and long run-out of a giant landslide.

A systematic approach for the assessment of flooding hazard and risk associated with a landslide dam

Inundation caused by landslide dams may occur in the upstream and downstream of the dams. A proper flooding hazard assessment is required for reaction planning and decision-making to mitigate possible flooding hazards caused by landslide dams. Both quick and detailed procedures can be used to evaluate inundation hazards, depending on the available time and information. This paper presents a systematic approach for the assessment of inundation hazards and risks caused by landslide dam formation and breaches. The approach includes the evaluation of dam-breach probability, assessment of upstream inundation hazard, assessment of downstream inundation hazard, and the classification of flooding risk. The proposed assessment of upstream inundation estimates the potential region of inundation and predicts the overtopping time. The risk level of downstream flooding is evaluated using a joint consideration of the breach probability of a landslide dam and the level of flooding hazard, which is classified using a flooding hazard index that indicates the risk of potential inundation. This paper proposes both quick and detailed procedures for the assessments of inundation in both the upstream and downstream of a landslide dam. An example of a landslide dam case study in southern Taiwan was used to demonstrate the applicability of the systematic approach.

The Hungtsaiping landslides: from ancient to recent

A large and deep-seated landslide at Hungtsaiping was triggered by the 1999 Chi-Chi earthquake with the magnitude of 7.3. Extensive site investigations for the landslide were conducted including field reconnaissance, geophysical exploration, borehole logs, and laboratory experiments. Thick colluvium was found around the landslide area and indicated the occurrence of a large ancient landslide. The Hungtsaiping area involves at least two large landslides events, an ancient rockslide and the 1999 colluvium slide. With the consideration of a source collapse mass, the two landslides in sequence are reasonably reproduced by the distinct element modeling. The modeling is calibrated by rock mass strength behavior through a procedure with the Hoek–Brown failure criterion, statistical experimental design, and optimization techniques. The mechanism of the 1999 landslide that cannot be revealed by the underground exploration data alone is clarified. The proposed procedure enables a rational and efficient way to determine micro-parameters for the distinct element modeling of landslides.

Velocity‐dependent frictional weakening of large rock avalanche basal facies: Implications for rock avalanche hypermobility?

To characterize the hypermobility mechanism of rock avalanches, a series of rotary shear tests at different shearing velocities (Veq) ranging from 0.07 m/s to 1.31 m/s and at a normal stress of 1.47 MPa were carried out on soil sampled from the basal facies of the Yigong rock avalanche that occurred in the Tibetan plateau in China. Through conducting these tests, the macroscale and microscale features of the deformed samples were analyzed in detail with the following valuable conclusions being reached: (1) soil subjected to rotary shear exhibits a clear velocity-dependent weakening characteristic with an apparent steady state friction of 0.13 being reached at Veq ≥ 0.61 m/s, (2) high-temperature rises and layers with high porosity were observed in the samples sheared at Veq ≥ 0.61 m/s, and (3) the cooperation of thermal pressurization and moisture fluidization induced by friction heating plays an important role in explaining the marked frictional weakening of the soil. In addition, the appearance of nanoparticles due to particle fragmentation should facilitate the weakening of the soil but is not the key reason for the marked frictional weakening.

DEBRIS-BUDGET-BASED DEBRIS-FLOW SUSCEPTIBILITY ANALYSIS

Susceptibility analysis of debris-flow is important for mitigating the induced hazards. This research proposed a statistical model for predicting the occurrence of debris-flow in Tungshih, Taiwan. Five causative factors including steepness of creek, catchment area, form factors, potentially landslide area and debris storage index were selected in the statistical model. Based on the record of debris-flow occurrence during typhoon Toraji, the steepness of creek, potentially landslide area and debris storage index were sieved as relevant causative factors of the occurrence of debris-flow. By taking the debris budget into account, the susceptibility of debris-flow will evolve with the landslide and debris-outflow. Thereafter, the impact of geological events, such as a large earthquake, on the occurrence of debris-flow can be predicted and quantitatively evaluated.

Normal Stress‐Dependent Frictional Weakening of Large Rock Avalanche Basal Facies: Implications for the Rock Avalanche Volume Effect

Rock avalanches, as an important geological hazard in mountainous regions, have drawn much scientific interest, especially in recent decades (Lucas et al. 2014). According to rough statistics, rock avalanches have caused billions of dollars in damage and many casualties over only the past few decades (Huang and Li 2009), highlighting the importance of rock avalanche studies. As reported in the literature, enormous volumes, extremely high velocities, and unexpectedly long runouts are three prominent features of rock avalanches (Pudasaini and Miller 2013), which are the main contributors to rock avalanche devastation. To learn the hypermobility of rock avalanches, rotary shear tests at shearing velocities (Veq) of 0.07–1.31 m/s and a normal stress (σ) of 1.47 MPa were conducted by Wang et al. (2017) using soil collected from the Yigong rock avalanche basal facies. In this experimental study, marked frictional weakening of the soil was attained at Veq ≥ 0.61 m/s, and concurrent large temperature increases, water vaporization, and high porosity layers were observed in the deformed samples. Accordingly, our research team proposed that thermal pressurization induced by frictional heating may be a key factor in the frictional weakening of the avalanche basal facies samples, which provides insight into rock avalanche hypermobility mechanisms. This discovery brings to mind another rock avalanche feature revealed by field data statistics: the reduction of Fahrböschung with increasing rock avalanche volume, i.e., rock avalanche volume effect (Pudasaini and Miller 2013; Lucas et al. 2014). Therefore, a pursue study on the role of normal stress in high-speed rock avalanche frictional sliding is conducted here to discover the mechanism behind the rock avalanche volume effect. With this study, some insights into the avalanche volume effect will hopefully be discovered through laboratory observations and theoretical analysis, which will enhance our understanding of rock avalanche dynamics.