Hideaki Marui

Review of Monitoring Parameters of the Kostanjek Landslide (Zagreb, Croatia)

Since 2011, in the framework of the Croatian-Japanese SATREPS FY2008 Project, scientists have been working on the establishment of the Kostanjek landslide monitoring system in the City of Zagreb (Croatia). External triggers at Kostanjek landslide are measured with rain gauge and accelerometers. Displacements at the surface are measured by GNSS sensors and extensometers, while subsurface displacement is measured by vertical extensometers and inclinometer. Hydrological measurements consist of groundwater level measurements, discharge measurements, chemical and isotope analysis. Monitoring sensors recorded landslide reactivation due to external triggers in the winter period of 2012/2013. During the period from September 2012 to March 2013 the total cumulative precipitation was 793.7 mm and horizontal displacements were in the range of 9–20 cm. The installed monitoring sensor network proved to provide reliable data for the establishment of relations between landslide causal factors and landslide displacement rates aimed at establishing threshold values for early warning system.

The First International Workshop on Warning Criteria for Active Slides: technical issues, problems and solutions for managing early warning systems

Early warning systems (EWSs) rely on the capacity to forecast a dangerous event with a certain amount of advance by defining warning criteria on which the safety of the population will depend. Monitoring of landslides is facilitated by new technologies, decreasing prices and easier data processing. At the same time, predicting the onset of a rapid failure or the sudden transition from slow to rapid failure and subsequent collapse, and its consequences is challenging for scientists that must deal with uncertainties and have limited tools to do so. Furthermore, EWS and warning criteria are becoming more and more a subject of concern between technical experts, researchers, stakeholders and decision makers responsible for the activation, enforcement and approval of civil protection actions. EWSs imply also a sharing of responsibilities which is often averted by technical staff, managers of technical offices and governing institutions. We organized the First International Workshop on Warning Criteria for Active Slides (IWWCAS) to promote sharing and networking among members from specialized institutions and relevant experts of EWS. In this paper, we summarize the event to stimulate discussion and collaboration between organizations dealing with the complex task of managing hazard and risk related to active slides.

Landslide Inventory in the Area of Zagreb City: Effectiveness of Using LiDAR DEM

Preliminary results of landslide mapping in the City of Zagreb (Croatia), obtained in the frame of the Japanese-Croatian scientific project, are presented in this paper. The aim of this research is to develop a method for landslide delineation in order to enable land use officials to implement this data to create more useful measures for landslide risk management. Selected landslides in the hilly zone of Mt. Medvednica were identified visually using LiDAR bare-earth DEMs. The results of data analysis will be implemented to perform a more comprehensive study of landslides in the entire pilot area (total area is 180km2).

Landslides and Multi-Hazards

Landslides occur frequently in connection with other types of hazardous phenomena such as earthquakes and volcanic activities. Strong earthquakes often cause a large number of landslides, including large-scale landslides, in mountainous areas. Volcanic activities could trigger giant landslides or debris avalanches on mountain slopes. It is not uncommon that such large-scale landslides cause river blockage and form natural dams, which are vulnerable to collapse by overtopping and breaching. The sudden collapse of a landslide dam can cause a catastrophic flood in the downstream area. Submarine landslides are also common phenomena. Large-scale submarine landslides cause catastrophic tsunamis. In assessing those catastrophic cases as a whole, it is necessary to pay special attention to extremely high threats to vulnerable settlements in hazardous areas. The risk assessment of such complicated combined landslide disasters around the world, particularly in developing countries, is a significant step for identifying the appropriate mitigation strategy against catastrophic damage. In recent decades we have experienced remarkable disasters induced by landslides. For example, a huge number of landslides were induced by the Chi-Chi earthquake in Taiwan (1999), by the Mid-Niigata Prefecture earthquake in Japan (2004) and the Northern Pakistan earthquake (2005). Most recently the Wenchuan earthquake occurred with magnitude 8.0 in central part of China on May 12, 2008. This gigantic earthquake caused a tremendous number of landslides, as seen in the satellite picture in Fig. 23.1. Large-scale landslides occurred in volcanic areas, such as at Stromboli Volcano in Italy (2002) (Fig. 23.2) and on Leyte Island in Philippines (2006) (Fig. 23.3). Whole such events manifest the significance of a thematic session within the First World Landslide Forum focussing on the issue of risk mitigation targeting “landslides and multi-hazards”.

Two Integrated Models Simulating Dynamic Process of Landslide Using GIS

Two major movement modes of slope failures: landslides and debris-flows are simulated by two integrated models using GIS to represent the dynamic process across 3D terrains. Landslides occur when earth material moves downhill after failing along a shear zone. Debris flows can be differentiated from landslides by the pervasive, fluid-like deformation of the mobilized material. The formation of debris flows most often occurs as a result of a landslide partially or completely mobilizing into a debris flow. GIS-based revised Hovland’s 3D limit equilibrium model is used to simulate the movement and stoppage of a landslide. The 3D factor of safety will be calculated step by step during the sliding process simulation. Stoppage is defined by the factor of safety much greater than one and the velocity equal zero. GIS-based depth-averaged 2D numerical model is used to predict the runout distance and inundated area of a debris flow. The simulation displays the propagation and deposition and deposition of a debris flow across the complex topography. The two GIS-based integrated models are able to provide effective tools for hazard mapping and risk assessment.

Three Dimensional Stability Analysis of the Grohovo Landslide in Croatia

The Grohovo Landslide, situated on the north-eastern slope in the central part of the Rjecina River valley, is the largest active landslide along the Croatian part of the Adriatic Sea coast. The Grohovo Landslide is also a key pilot area for implementation of the monitoring activities of the Japanese-Croatian joint research project on “Risk identification and land-use planning for disaster mitigation of landslides and floods in Croatia”. This complex retrogressive landslide was reactivated in December 1996. It is considered that the basal failure surface is positioned at the contact between the slope deposits and the flysch bedrock. Based on the data from boreholes, geological mapping, geophysical surveys and the geological cross-section of the slope, the three dimensional shape and the position of the sliding surface were simulated using the inverse distance weighted interpolation. Using 3D extended Janbu’s simplified method, global stability of the Grohovo Landslide and stability of 12 separate landslide bodies were analyzed.

Landslide Dams Formed by the 2004 Mid-Niigata Prefecture Earthquake in Japan

It was a remarkable aspect that a tremendous number of landslides were triggered by the Mid-Niigata Prefecture Earthqauke. Because the epicenter was located at a depth of 13 km just in the landslide prone area of central part of the Niigata Prefecture, severe damage was caused by the earthqauke-induced landslides. Furtehermore many landslide dams were formed mainly in the watershed of the Imogawa-River by the displaced soil mass of the earthquake-induced landlslides. Some large landslide dams should pose a great threat of flood and debris flow in case of dam collapse to the settlemnt of the Ryuko-District in the downstream area of the watershed. It was urgently needed to arrange the emergency operations to avoid the destructive collapse of the major landslide dams. This contribution illustrates overview of landslide dams and emergency operations against dam collapse.

Chemical Weathering and the Occurrence of Large-Scale Landslides in the Hime River Basin, Central Japan

The Hime River Basin is located in the northern part of Central Japan and is known as one of the areas where both erosional potential and sediment yield are extremely high in Japan. Landslides and debris flows triggered mainly by heavy rainfalls have frequently occurred in the basin. We have estimated the chemical weathering rates for nineteen watersheds in the Shirouma-Oike Volcano located in the western part of the basin. These rates have been simply estimated by the mass balance equation between solute fluxes of stream waters from each watershed and solute loss comparing fresh and weathered volcanic rocks and were calculated to be ranging from 0.15 to 3.24 mmyr-1. A watershed showing the highest rate of chemical weathering and solute flux corresponded to the area where the large-scale landslide occurred in 1911 and debris flows and landslides have continually occurred until now. Unstable sediments yielded by chemical weathering are thought to be an important factor of sediment disaster occurrences in the research area. Solute fluxes of each stream could be useful for susceptibility mappings of landslides and debris flows in each watershed.

Open image in new windowSimulation Model to Predict Landslide Speed Using Velocity-Dependent Viscous Damping

We propose a simulation model using viscous damping to predict the moving velocity (v) of a landslide before it reaches a strain limit. We call this model “Lumped mass damper model”, and it is based on a motion equation using a mass system model composed of a damper. The damper introduces a damping force in the opposite direction to the downward force (F) of the landslide, according to the landslide velocity. For slope-stability analysis, a simple model such as the Fellenius method is used. In the analysis, the resistance force (R) and driving force (D) are calculated in each individual slice and summed up for all slices. the safety factor (Fs) is indicated as Fs = R/D. Then, the equation of motion is shown as \( {\text{m}}\upalpha = {\text{F}} - {\text{A}} \cdot {\text{Cd}} \cdot {\text{v}} \). In the equation m is mass and α is acceleration of the landslide. After solving this motion equation, the formula ‘\( {\text{v}}{ \approx }{\text{F}}/{\text{A}} \cdot {\text{Cd}} \)’ is obtained. ‘A’ is the area of the slip plane of the landslide. ‘Cd’ is the viscosity coefficient of the damper, which exerts its effect on the slip surface of the landslide. Analytical results using this technique on the Kostanjek landslide in Croatia show that this Lumped mass damper model was able to reproduce the variations in landslide motion in response to the variation of groundwater level. Also, the Takino landslide of 4th August 1986 which was induced by embankment construction for a Japanese highway was successfully analyzed using this technique.

Earthquake-Induced Landslides: An Overview

Strong earthquake has been a significant triggering factor of landslides in hilly and mountainous areas. Damages caused by earthquake-induced landslides are sometimes larger than damages related to the shaking of the earthquake itself. During the last decades, a number of reports have been published to show serious damages caused by landslides after a series of disastrous earthquake events in mountainous regions. A lot of researches on landslides induced by earthquakes have been intensively carried out by various institutions. In 2012, the Japan Landslide Society published a book “Earthquake-induced landslides” in Japanese and further organized an International Symposium on Earthquake-induced Landslides in Kiryu City in Japan. Nowadays earthquake is still unavoidable and unpredictable. The study of earthquake-induced landslides has a major importance for better understanding of the causal mechanisms and the relationship among the landslide type, size, occurrence location and geomorphology. This paper presents an overview of current issues and recent advances concerning earthquake-induced landslides. It includes (i) movement types, characteristics and processes; (ii) causal mechanisms; (iii) physical and numerical modeling; (iv) secondary disasters; (v) risk assessment and management. It is urgently needed to develop practical methods for risk evaluation and hazard zoning on the basis of recent knowledge with appropriate mitigation strategy in order to avoid catastrophic damages by earthquake-induced landslides.