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The internal structure and geotechnical properties of landslide dams have rarely been examined in detail, although they largely control the longevity and potential failure mechanisms of the dams. During the 2004 Mid-Niigata Prefecture earthquake, thousands of landslides were triggered and many landslide dams were formed in the Imo River basin. Among these landslides dams, the biggest one that occurred in the Higashi-Takezawa district threatened both the upstream and downstream areas. Emergency and eventual permanent countermeasures were successfully performed to mitigate the hazards presented by the dam. The preserved landslide dam provides a good field study area for improving understanding of the formation and stability of similar features. To characterize its internal structure and to provide more reliable information for stability analysis, we used a multiple-channel surface-wave technique and microtremor array measurements to survey the dam's S-wave velocity (V-s) profile. Our results show that the integrated use of these methods is an effective approach for determining the S-wave velocity structure of landslide dams, irrespective of the mountainous environment in which they typically occur. The V-s profile suggests that the displaced landslide materials had been little disturbed during movement, although movement was rapid and over a long distance. We also discuss herein the landsliding mechanism and assess the breaching risk of the landslide dam due to overtopping. (C) 2016 Elsevier B.V. All rights reserved.

The Croatian-Japanese joint research Science and Technology Research Partnership for Sustainable Development (SATREPS) project ‘Risk Identification and Land-Use Planning for Disaster Mitigation of Landslides and Floods in Croatia’ was performed from 2009 to 2014. Key objectives of the project were landslides and floods hazard analysis and the development of guidelines for use in urban planning. This project is also designated as on-going IPL project 161. The aims of the working groups dealing with landslides were to establish a methodology of comprehensive real time monitoring at two most important landslides in Croatia based on the results of previous investigations and new in situ and laboratory testing and behavior analysis; laboratory soil testing and numerical modelling of static and dynamic landslide behavior; development of landslide inventories using direct sensing and remote sensing techniques followed by the development of methodologies of landslide hazard analysis and zonation in three pilot areas in Croatia. In this paper we will present the most important achievements of working groups related to landslide studies at the project pilot areas: two in Primorsko-Goranska County (the Rjecina River Basin and the Dubracina River Basin) and one in the City of Zagreb (a hilly area of Medvednica Mt.). The identification and mapping of existing landslides in the hilly area of Medvednica Mt., Dubracina River Basin and Rjecina River Basin so as establishment and results of the monitoring systems installed on the Grohovo Landslide and the Kostanjek Landslide will be described.

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.

最近, 大地震や豪雨を起因として河川を閉塞する大規模地すべりダムの発生が数多く見られている。地すべりダムの決壊による洪水は土石流となって下流に流下し, 人命や社会活動に激甚な被害を与える。このため地すべりダム決壊の予測手法の確立は非常に重要である。このため, 地すべりダムの既往災害データを用いてファジィif-thenルールのパターン識別解析によりその決壊の予測手法を検討した。パターン識別解析においては地すべり長さ/高さの比 (SFI) 及び貯水池容量/流域面積の比 (CAI) の新たな属性要因の指標を導入することによって地すべりダムの決壊の予測精度が10%以上も向上することを明らかにした。また, 当解析より得られたファジィif-thenルールより地すべりダムの属性要因のその決壊に及ぼす影響度を明らかにした。

パキスタン北部を流れるフンザ川右岸のアッタバードにおいて2010年1月初旬に幅1000m, 比高1000m, 斜面長1500mの規模で地すべりが発生し, 約4000万立方mの移動土塊がフンザ川河谷をせき止めた。移動体は, 青灰色細粒物質をマトリックスとした長軸方向で3-4mから10mに及ぶような岩屑層からなり, この移動体からさらに絞り出された細粒物質が地すべりマウンド上を泥流となって下流側や上流側に流れ下った。本地すべりによる犠牲者は死者19人で, そのすべてはこの泥流に巻き込まれたことによるものである。この地すべりダムは大きな岩屑層からなるため突然決壊の危険性は低いと考えられた。災害4ヶ月前に撮影されたALOS/PRISM画像の実体判読の結果, 谷壁斜面には前兆現象的な変位が認められた。このためヒマラヤなどの高起伏地域での河道閉塞を引き起こす大規模地すべりの事前把握のための衛星画像利用の可能性が示唆された。

地震時の地すべり・土砂災害の被害を抑制するためには危険箇所の緊急点検等の対応を迅速・的確に行う必要がある。地すべり等を引き起こす斜面安定度の低下は水文状態と地震動とに影響される。水文状態については, 北陸地方で適用可能な広域水文指標が提案されている。地震動については, 全国の市町村単位で震度が計測されている。これにより, 市町村単位で水文状態と震度とを監視することが可能である。北陸地方で最近3ヵ年に発生した比較的大きな3つの地震災害については, 危険箇所緊急点検が行われ, 市町村単位で危険度判定が実施されてきた。そこで, 本研究では危険度判定により対策が必要とされた事例を水文指標と震度を用いて分析した。これにより, 地震発生時に, 震度が一定以上の区域内を対象とした危険箇所の崩壊危険性を, 水文状態と震度とから推定する手法を構築した。地震時の危険箇所の崩壊危険性は, 広域の水文状態を考慮することで, より精密に推定できることが示された。いくつかの広域水文指標について, 一定の閾値以上の震度の領域を点検対象とした場合に危険性の高い箇所を見出す的中率と捕捉率との比較を実施した。

In order to study the physical and chemical weathering and their impact on the shear strength of the soil mass, soil samples were collected from different depths ranging from the ground surface to a depth of 15m at two different drainage wells in a Mukohidehara landslide area. These specimens represent the residual soil near the surface, specimen at a depth range of ground water level fluctuation, less weathered specimen from the depth below the ground water level fluctuation, the remolded soil from sliding zone and the specimen below sliding zone. Measurement of Atterberg's limits, particle size analysis, X-ray diffraction analysis, slake durability test and X-ray fluorescence tests were carried out. Drained simple shear tests, and drained ring shear tests were also conducted on those specimens to measure their strength characteristics.Test results showed that fully softened shear strength of the less weathered specimen was very close to the peak shear strength of the specimen from the sliding zone. Test results showed no significant variations of index properties (liquid limit, plasticity index and clay fraction) , mineral compositions and chemical compositions with depth. Residual shear strengths of the specimen also did not vary much with depth. In order to compare these findings with rocks from the other types of formation, specimens were collected from the ground surface, ground water fluctuation zone, less weathered zone and sliding zone of three other landslides sites. The test results on the index properties, shear strength properties, mineralogical analysis, and bulk chemistry, of those landslides were consistent with the findings in Mukohidehara landslide.The test results of this study suggested that physical weathering plays a major role in the reduction of shear strength of mudstone, in comparison to the chemical weathering in the form of mineralogical and chemical alteration. Test results also suggested that physical weathering by slaking and disintegration is significant at ground water fluctuation zone in those mudstone formations.

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.

Landslide, debris flow and rockfall are the main geohazards in the Rjecina River catchment. The Grohovo landslide is located on the northeastern slope in the central part of the Rjecina river valley just downstream of the Valici dam. As the effects of intense rainfall or earthquake, two potential geohazard events could occur. One scenario is that the slope deposits of Grohovo landslide moving towards the channel of the Rjecina River will form a landslide-dam. Another scenario is that the slope deposits mixing with water will form a debris flow arriving at the City of Rijeka. In this paper, the formation of landslide-dam and the debris-flow are simulated by two integrated models using GIS to represent the dynamic process across 3D terrains. GIS-based revised Hovland’s 3D limit equilibrium model is used to simulate the movement and stoppage of the slope deposits to form landslide-dam. The simulation result shows about 9 m landslide-dam formed. GIS-based depth-averaged 2D numerical model is used to predict the runout distance and inundated area of a debris flow. As a result, the simulated debris-flow takes about 16 min to travel about 6 km along the Rjecina River valley arriving at the City of Rijeka.

Debris flows triggered by earthquake show different occurrence mechanism, movement characteristics and failure modes with the common debris flows under gravity, because of the influence of seismic force, snowpack, different topography, lithology etc. In this paper, the Tatsunokuchi debris flow induced by the 2011 Northern Nagano Prefecture Earthquake and Dozou-sawa debris flow caused by the 2008 Iwate-Miyagi Nairiku Earthquake are analyzed. The two debris flows can be considered as composite actions of seismic force and snow. This paper compares the occurrence conditions, movement processes and geomorphic characteristics of the two debris flows and simulates the runout distance and inundated area using a GIS-Based depth-averaged two-dimensional numerical model. The simulations reproduce the propagation and deposition across the actual three-dimensional topography and the results are in good agreement with the investigation by comparing with the photographs. The entrained-snow along the flow path alters the speed and runout distance of the debris flows. The lubricating effect of snow in the movement process is discussed.

Most of the slope failure disasters in a humid area such as that of Japan are caused by heavy rain. However, even for the case of heavy rainfall that occurs once in every 10 years, total area of slope failures seldom exceeds 10% of a watershed. From this background, we focused on the vein-like groundwater flows that increase pore-water pressure, and clarified the relationship between distributions of slope failures and groundwater veins. In this study, a 1-m-depth ground temperature survey and water-chemistry analyses at springs and boreholes were conducted in Zentoku area of Shikoku Island, southwestern Japan, to grasp the distribution of groundwater veins and their sources. Subsequently, slope-stability was analyzed to investigate the relationship between groundwater veins and slope failures at study sites. These results lead to the following conclusions: The slope failures appear to concentrate around shallow groundwater veins and groundwater veins rising from deep layers. This means that slope failures caused by these groundwater veins in addition to rainfall. Two types of groundwater originate in the deep layers: one has short storage time as indicated by the fact that dissolved substances are low; the other is stored for a lengthy period as noted by a high concentration of dissolved substances. By combining the results of stability analyses and distribution of groundwater veins, it is suggested that prediction of zones with high potential for slope failure can be more accurate.

Slope stabilization procedures for seven landslides in the Niigata Prefecture of Japan had provided an excellent and rare opportunity to examine the composition of ground water, and residual shear strength of the sliding surface soil, as well as unsheared mudstone. Ring shear tests were conducted on the soil samples collected from sliding surface soil, revealed during the installation of 3 m diameter drainage galleries. Shear strength and index properties of the soil were measured by mixing the soil with distilled water and sea water, and after leaching the NaCl from the pore water. The residual shear strength of the soil sample with distilled water was 3–5° lower than that with the sea water. The residual shear strength of the intact rock powder after leaching the dissolved salt was close to that of the soil from sliding surface, and the residual shear strength of the soil from sliding surface after mixing with sea water was close to that of the intact rock powder. The increase in residual shear strength...

A sufficient knowledge on the kinematics and development of landslides helps to adopt proper measures that can be used to protect slopes and the environment in general. This can be achieved by adequate monitoring programs. This paper presents the findings of intensive monitoring activities carried out on Shiidomari and Katanoo landslides found in Sado Island of Japan. More than one year of observation of the two landslides allowed defining some peculiar futures of their kinematics and style of development. The problem of slope instability in the two areas is generally accredited to various factors. But, both landslides were triggered by heavy rainfalls and snowmelt. Because of the outline of the area and the presence of relict topographic features, the Shiidomari landslide is considered to be a large-scale reactivation of old slope failures. The Katanoo landslide is, however, a first-time case. Geophysical investigations and drilling activities in Shiidomari indicated the presence of two slip planes. The deepest (80–100 m) of these is controlled by existing lineaments. Monitoring data suggests that the body of the landslide has subsided as much as 1.16 m just below the main scarp, but a centimeter in the central region. The toe sector also experienced a significant amount of subsidence, but this was counter-balanced by an uplift on the opposite side of the landslide. Hence, the landslide seems not any more active along the deepest slip surface, although it may extend upward and define a series of shallow shear planes around the crown. In the case of Katanoo, the landform characteristics, differential weathering, the road cut and groundwater fluctuations appeared to contribute much to determine the exact location of the landslide. Extensional cracks that preceded the landslide can be related to heavy rainfalls and the cold and warm cycles thereafter. Subsurface investigations and monitoring works indicated that the landslide has two slide blocks with different slip planes. During the observation period, the upper part of the landslide responded more effectively to rainfall and snowmelt than the middle and lower sections. The corresponding movements, however, appeared to settle about three months after failure. There were also little strain transmissions in boreholes and no significant change in the characteristics of the landslide. The kinematics of deformation of many of the slopes in Sado Island resembles that of Shiidomari landslide. But mass movements along highways and mountain roads are usually similar to Katanoo. Landslides of the type like Shiidomari may not show sudden and drastic failures, but are usually long lasting and can reactivate repeatedly along new, shallow shear planes. Monitoring works and long-term supervisions in these types of landslides are useful to identify impending failures and take the right measures before they brought about large-scale destruction to the environment.

Slope instability research and susceptibility mapping is a fundamental component of hazard management and an important basis for provision of measures aimed at decreasing the risk of living with landslides. On this basis, this paper presents the result of a comprehensive study on slope stability analyses and landslide susceptibility mapping carried out in part of Sado Island of Japan. Various types of landslides occurred in the island throughout history. Little is known about the triggering factors and severity of old landslides, but for many of the recent slope failures, the slope characteristics and stratigraphy are such that ground surfaces retain water perennially and landslides occur when additional moisture is induced during rainfall and snowmelt. A range of methods are available in literature for preparation of landslide susceptibility maps. In this study we used two methods namely, the analytical hierarchy process (AHP) and logistic regression, to produce and later compare two susceptibility maps. AHP is a semi-qualitative method, which involves a matrix-based pair-wise comparison of the contribution of different factors for landsliding. Logistic regression on the other hand promotes a multivariate statistical analysis with an objective to find the best-fitting model that describes the relationship between the presence or absence of landslides (dependent variable) and a set of causal factors (independent parameters). Elevation, lithology and slope gradient were casual factors in this study. The determinations of factor weights by AHP and logistic regression were preceded by the calculation of class weights (landslide densities) based on bivariate statistical analyses (BSA). The differences between the AHP derived susceptibility map and the logistic regression counterpart are relatively minor when broad-based classifications are considered. However, with an increase in the number of susceptibility classes, the logistic regression map gave more details but the one derived by AHP failed to do so. The reason is that the majority of pixels in the AHP map have high values, and an increase in the number of classes gives little change in the spatial distribution of susceptibility zones in the middle. To verify the practicality of the two susceptibility maps, both of them were compared with a landslide activity map containing 18 active landslide zones. The outcome was that the active landslide zones do not completely fit into the very high susceptibility class of both maps for various reasons. But 70% of these landslide zones fall into the high and very high susceptibility zones of the AHP map while this is 63% in the case of logistic regression. This indicates that despite the skewed distribution of susceptibility indices, the AHP map was better to capture the reality on the ground than the logistic regression equivalent.

Slope stabilization procedures for six landslides in the Niigata prefecture in Japan afforded an excellent opportunity to examine the residual drained shear strength of weathered mudstones. Installation of 3 m diameter drainage galleries allowed undisturbed block samples to be collected which contained the slickenside surface of the failure plane. Ring shear tests were conducted on undisturbed samples and remolded samples of the same material. In addition to the laboratory testing, back analysis was performed to calculate the residual shear strength parameters of the slopes. Good agreement was found between the residual friction angles determined from back analysis, tests on undisturbed samples, and tests on remolded specimens. Many of the landslide materials exhibited a small cohesion at low values of effective normal stress, but the secant friction angle achieved a constant value at higher normal stresses.

Mineralogical composition, measured with x-ray diffraction for soil specimens collected from more than 80 natural disaster areas, show smectite, kaolinite, mica, feldspar, and quartz as major constituent minerals. Based on the results of more than 35 mixtures of smectite, kaolinite, and quartz in different proportions, a new correlation method was proposed for estimation of the residual friction angle ( ϕr′ ) with the proportion of the minerals. The mineralogical compositions of the natural samples were used to estimate the ϕr′ based on the proposed triangular model. The estimation method resulted in values as close as 90% to the measured ϕr′ , and as close as 80% to the case of 53 samples tested by other researchers. The paper incorporates the correlation of ϕr′ with the liquid limit, the plasticity index, the clay fraction, the specific surface area, and the proportion of smectite. Various ranges are proposed, according to the influence of the constituent clay minerals. In addition, the applicable range...

NaCl solution has significant effect on the residual shear strength of soil from mudstone areas. Soil samples were collected from the intact rock (unsheared zone) and sliding surface (sheared zone) of five mudstone landslide areas. Mixtures of distilled water and the intact rock possessed higher electric conductivity than those of distilled water and the sliding surface soil. When these samples were leached with distilled water for five times, they showed a substantial decrease in the electric conductivity. The residual shear strength varies according to the NaCl concentration in the pore water. Ring shear tests were also carried out in the commercial standard clays as bentonite and kaoline to understand the shear strength characteristics of the mudstone soils. When bentonite was treated with NaCl solution as pore water, it showed about three times increase in residual shear strength and decrease to one quarter in liquid limit. The effect of NaCl solution as pore water in kaoline was comparatively low. The residual shear strength of soil from mudstone area also increased when it was treated with NaCl solution as pore water. The result of the X-ray diffraction analysis showed that the proportion of smectite is higher than that of kaolinite in the residual soil from mudstone. These smectite minerals were found to be highly sensitive to NaCl solution. Because of the sensitive changing character of smectite minerals to NaCl solution, soil samples with NaCl rich water showed lower value in consistency limits and higher value in the residual shear strength compared to soil samples with distilled water. The findings suggest that the residual shear strength and index properties should be considered as variable properties as a result of the change in the pore water. Such properties are useful to understand frequent re-activation of the landslide occurring in the mudstone areas.

本論文では, 東北地方の第三紀層地すべり地における水質調査結果に基づき, 大規模地すべり地における地下水流動機構に関する総合的考察を行った。水質調査結果を地下水位調査結果, 地下水追跡調査, 更には地質構造と対比し, 総合的な地下水解析を行うことが有効であることを示した。滝坂地すべり地を対象とした解析では, 地下水位の変動タイプを地質・地すべりブロック別に考慮し, 地下水水質並びに地下水追跡調査結果を組み合わせることで地下水の流動状況を把握した。更に, 地すべり地内における地下水のCl-イオン濃度分布の調査結果に基づいて, 融雪期の地下水位の上昇に花崗岩体を通過してくる深層地下水が関与している可能性が高いことを示した。平根地すべり地を対象とした解析では, 新第三紀層中から流入する地下水と, 地下深部から上昇してくる地下水の混合状況から, 各地すべりブロックにおける地下水流動状況を把握した。水質解析結果から推定された地下水流動状況は地下水追跡試験結果と合致している。以上の考察結果を総合して, 大規模地すべり地における総合的な地下水流動特性の解析手法を提案した。

On January 5, 2000, a landslide of debris avalanche type (Cruden and Varnes, 1996), took place on the steep slope along the Tozawagawa river, upper tributary of Aganogawa river in Niigata Prefecture, Japan. This landslide blocked the Tozawagawa River, forming a natural dam 500m long temporarily. This landslide has been changing in form in short times just after the catastrophic event on January 5, 2000. In this paper, we are describing the sequence of the landslide using the aerial photographs taken in 1947 up to 2001, and are showing the scale and volume calculation using the aerial photographs.

新潟県東頸城地域の地すべり地では高濃度Na-Cl型地下水がしばしば見出される. 本研究では, 宇津俣地すべり地等で電気伝導度計を用いた詳細な地下水 (孔内水) 検層, 地下水の化学分析, ならびに酸素同位体比測定を実施した. その結果, 滑動が活発な地すべり土塊における地下水断面では, 化学躍層的な電気伝導度の急激な増加があり, 不活発な地すべり土塊では電気伝導度の有意な変化は認められない. 地すべり土塊内における地下水の水質は, 表層部より深部へ向かって, (1) Ca-HCO3, Na. Ca-HCO3型, (2) Na-SO4型, (3) Na-HCO3型, および (4) Na-Cl型に分類される. 酸素同位体比と塩化物イオン濃度の関係より, Na-Cl型地下水は西山層相当の続成作用を被った化石海水と天水起源の地下水との混合によって形成された. Na-Cl型地下水は異常高圧熱水としての深部化石海水が断層に沿って上昇し, 地すべり土塊に供給されていることを示唆する.

On 5 January 2000, a landslide occurred along the right flank of the upper tributary of the Tozawagawa River in Niigata Prefecture, Japan. The landslide blocked the river and formed a temporary lake approximately 670 m long and 11 m deep. In this report, we estimated a time series of aerial photographs from 1947, 1976, 2000, and 2001 to describe the sequences of the landslide. There are some indications that the landslide is a reactivation of an old failure that occurred before 1947. In addition, we have attempted to calculate the scale and volume by aerial photogrammetry.

During the heavy rain on June 29, 1999, four slope failures occurred around the Taishi-do area in Zentoku landslide, Tokushima, Japan. Based on field investigation after these failures, and the monitored records of the three-dimensional shear displacement me-ters before the failures, it was made clear that 1) the failures were limited comparing to the rainfall ; 2) One of the failures showed precursory displacement of creeping failure. To clarify the failure mechanism, field investigations including one-meter depth of soil temperature survey, temperature measurements of spring water and groundwater in borehole were conducted, and pore water pressures generated at failure were estimated through back-analysis. Thereafter, the relationship between the location of failed slopes and flowing groundwater veins, and the relationship between groundwater vein and precursory displacement of failures were analyzed. It is found that: 1) Slope failure occurred above or near groundwater vein ; 2) There were two types of groundwater veins, one was surficial vein type with high water temperature, and the other was deep vein type originating from a depth between 49 and 70m with low water temperature ; 3) The precursory displacement of the creeping failure was associated with the groundwater vein.

Since 2011, in the frame of the Croatian- Japanese SATREPS FY2008 Project, the 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 to 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.