Scale-invariance of soil moisture variability and its implications for the frequency-size distribution of landslides

Power spectral analyses of soil moisture variability are carried out from scales of 100 m to 10 km on the microwave remotely-sensed data from the Washita experimental watershed during 1992. The power spectrum S(k) has an approximate power-law dependence on wave number k with the exponent −1.8. This behavior is consistent with the behavior of a stochastic differential equation for soil moisture at a point, and it has important consequences for the frequency-size distribution of landslides. We present the cumulative frequency-size distributions of landslides induced by precipitation in Japan and Bolivia as well as landslides triggered by the 1994 Northridge, California earthquake. Large landslides in these regions, despite being triggered by different mechanisms, have a cumulative frequency-size distribution with a power-law dependence on area with an exponent ranging from −1.5 to −2. We use a soil moisture field with the above statistics in conjunction with a slope stability analysis to model the frequency-size distribution of landslides. In our model, landslides occur when a threshold shear stress dependent on cohesion, pore pressure, internal friction and slope angle is exceeded. This implies a threshold dependence on soil moisture and slope angle since cohesion, pore pressure and internal friction are primarily dependent on soil moisture. The cumulative frequency-size distribution of domains of shear stress greater than a threshold value with soil moisture modeled as above and topography modeled as a Brownian walk is a power-law function of area with an exponent of −1.8 for large landslide areas. This distribution is similar to that observed for landslides. The effect of strong ground motion from earthquakes lowers the shear stress necessary for failure, but does not change the frequency-size distribution of failed areas. This is consistent with observations. This work suggests that remote sensing of soil moisture can be of great importance in monitoring landslide hazards and proposes a specific quantitative model for landslide hazard assessment.     

Using an airborne laser scanner for the identification of shallow landslides and susceptibility assessment in an area of ignimbrite overlain by permeable pyroclastics

An airborne laser scanner can identify shallow landslides even when they are only several meters in diameter and are hidden by vegetation, if the vegetation is coniferous or deciduous trees in a season with fewer leaves. We used an airborne laser scanner to survey an area of the 1998 Fukushima disaster, during which more than 1,000 shallow landslides occurred on slopes of vapor-phase crystallized ignimbrite overlain by permeable pyroclastics. We identified landslides that have occurred at the 1998 event and also previous landslides that were hidden by vegetation. The landslide density of slopes steeper than 20° was 117 landslides/km² before the 1998 disaster. This event increased the density by 233 landslides/km² indicating that this area is highly susceptible to shallow landsliding.     

碳酸盐岩风化成土过程中的微生物作用

碳酸盐岩风化作用长期受到广泛关注,有关其成土的物源也一直是颇有争议的问题。基于前人有关碳酸盐岩风化成土作用的研究基础和对有关资料的调研与分析,结合各类研究成果,笔者提出了喀斯特地区岩石微生物的风化成土作用途径:微生物生长对矿物养料的吸收,以及分泌的代谢产物导致碳酸盐岩的破坏分解和一些次生矿物的形成;一些岩石微生物能够通过新陈代谢固定大气中的碳素和氮素,截留由雨水、风尘、大气气溶胶甚至空气流动所带来的土壤颗粒等外来物质。微生物在岩石表面与缝隙中的生长繁殖在碳酸盐岩风化成土这一漫长的地质演化过程中发挥了不可替代的重要作用。     

Influence of ignimbrite on the chemistry of river water in Shirasu plateau,Japan

River, rain and spring water samples from a region covered in “Shirasu” ignimbrite were collected on Kyushu Island, Japan. The analytical results were subjected to multivariate statistical analysis and stoichiometric calculation to understand the geographical distribution of chemical components in water and to extract geochemical underlying factors. The multivariate statistical analysis showed that the river-water chemistry is only slightly influenced by hot springs or polluted waters, but is highly controlled by weathering of ignimbrite. On the basis of the stoichiometric calculation based on water–rock interaction, the water chemistry was successfully estimated by a simple equation:\({\left[ {{\text{Si}}} \right]}{\text{ = 2}}{\left[ {{\text{Na}}^{{\text{ + }}} } \right]}{\text{ + }}{\left[ {{\text{Mg}}^{{{\text{2 + }}}} } \right]}\) in the upstream area, complemented by \({\left[ {{\text{Si}}} \right]}{\text{ = }}{\left[ {{\text{Na}}^{{\text{ + }}} } \right]}{\text{ - 3}}{\left[ {{\text{K}}^{{\text{ + }}} } \right]}{\text{ + }}{\left[ {{\text{Mg}}^{{{\text{2 + }}}} } \right]}{\text{ - 2}}{\left[ {{\text{Ca}}^{{{\text{2 + }}}} } \right]}\) in the downstream area.     

黄土台缘滑坡地表水入渗问题分析

黄土塬区提灌工程保证了农业生产,却造成了地下水位大幅抬升,使得近年来黄土台缘滑坡不断发生。黄土滑坡一个普遍特征就是后缘发育地裂缝以及落水洞,使地表水（灌溉水以及降雨）直接灌入坡体,诱发了大量黄土滑坡。因此,地表水入渗对于黄土滑坡机理研究以及滑坡防治具有重要意义。文章基于对陕西泾阳南塬黄土滑坡的现场调查,对黄土台缘滑坡地表水入渗工程地质问题进行了初步分析,包括：①地表水入渗与落水洞形成机制;②地表水入渗途径及其与黄土滑坡发育过程的关系;③降雨因素对于黄土滑坡的影响程度。     

中国滑坡降雨试验的研究现状与发展趋势

滑坡是世界上分布最广、危害最严重的地质灾害类型。降雨等因素作用下滑坡沿着滑动面发生剪切大变形,造成抗滑结构发生剪切破坏,然而目前抗滑结构设计未能充分考虑滑坡剪切大变形的静态、刚性设计,亟需开展滑坡-韧性锚固体系演化机理的深入研究。本文基于塑性变形理论提出了一种韧性锚固结构,建立了其力学模型,并以开挖后种蜂场滑坡为原型,设计了模型试验,对比分析了有无锚杆加固下边坡体变形、土压力等多源数据变化规律,结果发现：(1)韧性锚杆加固作用下边坡内测点侧向应力分布与曲线形态发生显著变化,边坡抗滑力增大了20%。(2)边坡剪切大变形过程中,韧性锚杆轴力呈周期性变化,与理论相符。(3)韧性锚杆明显减少了边坡位移及变形破坏范围,滑动范围减少了约25%。     

Soil moisture potential and water content in the unsaturated zone within the arid Ejina Oasis in Northwest China

Three soil profiles were selected in the Ejina Oasis, northwest China, to determine water content profiles and evolution of soil moisture potentials in the unsaturated zone within the arid area. The total soil moisture potentials have been monitored for about 3 months in 2001 at different depths in the soil profiles. The occurrence and movement of water in the unsaturated zone was analyzed using the zero flux plane (ZFP) method. It is shown that convergent ZFPs and divergent ZFPs may occur at depths between 0.5 and 3.0 m, and that the depth of the ZFPs was controlled by the root zone of plants growing on the land surface. Profiles of the total soil moisture potentials were observed to be coincident with those of the water contents at the three experimental sites. The total soil moisture potential showed a slight increasing trend and the ZFPs tend to vanish from summer to winter as the water extraction by roots decreased. Evapotranspiration through vegetation has an important bearing on the water content and the total potential in the unsaturated zone.     

Distribution of landslides adjacent to the northern side of the Yarlu Tsangpo Grand Canyon in Tibet, China

This paper presents results of recent studies on distribution and category of landslides in one section of the Sichuan–Tibet Highway, adjacent to the northern side of the Yarlu Tsangpo Grand Canyon, Tibet, Southwestern China. In the tectonic setting predominated by compression and strike-slipping, active faults are dominant and result in the genesis of the great alpine relief together with fluvial incision and unloading. In this section, with a distance of about 290 km between Ranwu and Lulang, 34 landslides occurred. Among them, the 12 large and super-large landslides comprise the most dangerous part of the highway system to road users over the past 50 years. The landslides usually occurred in slopes comprised of moraine with a large thickness, fluvio-pluvial and lacustrine deposits and fractured rocks. Based on the examination of the physical geography, structural geology, Quaternary geology, stratigraphy and petrography, this paper presents the temporal-spatial distribution of landslides along the section and classification of them into three types with respect to mechanism and composites of landslides.

Micro-sheeting of granite and its relationship with landsliding specifically after the heavy rainstorm in June 1999, Hiroshima Prefecture, Japan

Certain types of granite in mountainous areas are microscopically sheeted to a depth of 50 m due to unloading under the stress field that reflects slope morphology. Micro-sheets generally strike parallel to major slope surfaces and gently dip downslope, forming cataclinal overdip slopes. The cataclinal overdip slope accelerates creep movement of micro-sheeted granite, which in turn loosens and disintegrates granite via the widening or neoformation of cracks, probably in combination with stress release, temperature change, and changes in water content near the ground surface. The surface portion of micro-sheeted granite is thus loosened with a well-defined basal front, which finally slides in response to heavy rain. Innumerable landslides of this type occurred in Hiroshima Prefecture, western Japan, following the heavy rainstorm of 29 June 1999. Following such landslides, the weathering of micro-sheeted granite exposed on the landslide scar recommences, setting the stage for future landslide.     

Using hydrogen,oxygen, and tritium isotopes to identify the hydrological factors contributing to landslides in a mountainous area,central Taiwan

Over a 1-year period, 343 samples, including precipitation, creek, pond, and groundwater, were collected from June 2003 to May 2004. Analyses were performed for stable oxygen and hydrogen isotope compositions. Selected samples were also analyzed for tritium. The goal was to identify possible hydrologic factors contributing to a severe landslide in the Li-Shan area, central Taiwan. The isotope characteristics indicate that groundwater from Fu-Shou-Shan farm located up-slope from the landslide area is a major source for slope groundwater, in addition to precipitation. The groundwater is mainly recharged by pond water at Fu-Shou-Shan farm. According to the calculation of a two-end member equation with δ ¹⁸O, the contribution of farm groundwater to slope groundwater is significantly higher than that of precipitation, up to a factor of five. The estimated drainage efficiency of the existing system is only 23%. Draining off the slope groundwater in the up-slope region to decrease farm groundwater flow into the slope area is a feasible strategy to effectively reduce the risk of landslide.     

Erratum to: Early warning of rainfall-induced shallow landslides and debris flows in the USA

The state of knowledge and resources available to issue alerts of precipitation-induced landslides vary across the USA. Federal and state agencies currently issue warnings of the potential for shallow, rapidly moving landslides and debris flows in a few areas along the Pacific coast and for areas affected by Atlantic hurricanes. However, these agencies generally lack resources needed to provide continuous support or to expand services to other areas. Precipitation thresholds that form the basis of landslide warning systems now exist for a few areas of the USA, but the threshold rainfall amounts and durations vary over three orders of magnitude nationwide and over an order of magnitude across small geographic areas such as a county. Antecedent moisture conditions also have a significant effect, particularly in areas that have distinct wet and dry seasons. Early warnings of shallow landslides that include specific information about affected areas, probability of landslide occurrence, and expected timing are technically feasible as illustrated by a case study from the Seattle, WA area. The four-level warning scheme (Null, Outlook, Watch, Warning) defined for Seattle is based on observed or predicted exceedance of a cumulative precipitation threshold and a rainfall intensity–duration threshold combined with real-time monitoring of soil moisture. Based on analysis of historical data, threshold performance varies according to precipitation characteristics, and threshold exceedance corresponds to a given probability of landslide occurrence. Experience in Seattle during December 2004 and January 2005 illustrates some of the challenges of providing landslide early warning on the USA West Coast.     

Recurrent events on a Quaternary fault recorded in the mineralogy and micromorphology of a weathering profile, Yangsan Fault System, Korea

Recurrence characteristics of a Quaternary fault are generally investigated on the basis of field properties that are rapidly degraded by chemical weathering and erosion in warm humid climates. Here we show that in intense weathering environments, mineralogical and micromorphological investigations are valuable in paleoseismological reconstruction. A weathering profile developed in Late Quaternary marine terrace deposits along the southeastern coast of the Korean Peninsula was disturbed by tectonic movement that appears to be a simple one-time reverse faulting event based on field observations. A comparative analysis of the mineralogy, micromorphology, and chemistry of the weathering profile and fault gouge, however, reveals that both the microfissures in the deformed weathering profile and larger void spaces along the fault plane were filled with multi-stage accumulations of illuvial clay and silt minerals of detrital origin, suggesting a repetition of fissuring and subsequent sealing in the weathering profile as it underwent continuous mineralogical transformation and particle translocation. We reconstruct a sequence of multiple faulting events unrecognized in previous field surveys, which requires revision of the view that the Korean Peninsula was tectonically stable, during the Late Quaternary.     

鄂尔多斯盆地东部奥陶系风化壳储层特征及主控因素分析

鄂尔多斯盆地东部奥陶系风化壳储层岩石类型以含膏模孔的细粉晶白云岩为主。储集空间主要为溶孔,溶孔的充填程度及类型决定了储层物性的好坏。充填物类型决定储集空间的好坏,方解石充填对储集空间破坏性较大,但充填白云石由于其自身晶粒较粗,发育晶间孔,对储集空间具有建设性作用。对盆地东部风化壳储层发育的表征形态及孔洞充填物的硫同位素、化学成分、激光碳氧同位素、锶同位素特征的分析表明,盆地东部岩溶孔洞中充填的方解石主要形成于裸露风化期,而白云石则是埋藏期压释水岩溶的产物,提出中深埋藏期的压释水岩溶是有利储层形成的关键因素。     

Probabilistic landslide susceptibility mapping in the Lai Chau province of Vietnam: focus on the relationship between tectonic fractures and landslides

This study evaluates the susceptibility of landslides in the Lai Chau province of Vietnam using Geographic Information System (GIS) and remote sensing data to focus on the relationship between tectonic fractures and landslides. Landslide locations were identified from aerial photographs and field surveys. Topographic, geological data and satellite images were collected, processed, and constructed into a spatial database using GIS data and image-processing techniques. A scheme of the tectonic fracturing of crust in the Lai Chau region was established. Lai Chau was identified as a region with many crustal fractures, where the grade of tectonic fracture is closely related to landslide occurrence. The influencing factors of landslide occurrence were: distance from a tectonic fracture, slope, aspect, curvature, soil, and vegetative land cover. Landslide prone areas were analyzed and mapped using the landslide occurrence factors employing the probability–frequency ratio model. The results of the analysis were verified using landslide location data and showed 83.47% prediction accuracy. That emphasized a strong relationship between the susceptibility map and the existing landslide location data. The results of this study can form a basis stable development and land use planning for the region.     

High resolution mapping,description and interpretation of the foreshore in front of the great undercliff landslides; the Plateau,Dowlands and Bindon within the Axmouth to Lyme Regis Undercliffs National Nature Reserve,south Devon coast,England, and how that might inform understanding of the mechanisms of failure

The Axmouth to Lyme Regis Undercliff National Nature Reserve contains three highly unusual landslides; the Plateau, Dowlands and Bindon. The failure surface of the Plateau landslide is clearly within the Triassic strata rather than on the Jurassic-Cretaceous unconformity, which is the primary failure surface elsewhere along this coast. The nature of the famous Bindon Landslide of 1839, which formed Goat Island and the Chasm, has been the subject of much debate since it was first described by Buckland and Conybeare in 1840. While it is broadly agreed to be a translational failure, the stratigraphic location of the failure surface is still not agreed. This paper examines the Plateau slip in detail and attempts to apply what can be seen there to Dowlands and Bindon. While Pitts undertook a highly detailed mapping exercise of the landslides throughout the undercliff itself, he did not map the foreshore in any detail. Therefore an Unmanned Aerial Vehicle or drone was used to generate a high resolution photomontage of the foreshore in front of all three landslides to enable detailed mapping of the features contained within it. The results are available on the web. The mapping does not resolve the question of the location of the failure surface of both Dowlands and Bindon but it provides further detail for interpretation.     

土壤水分对土壤参数的敏感性及其参数优化方法研究

利用2008年1月1日至2009年9月31日黑河流域阿柔冻融观测站的气象和土壤水分数据,采用基于方差的多参数敏感性分析方法研究通用陆面模型(Common Land Model,CoLM)模拟的土壤水分对土壤质地(砂土和黏土)的敏感性,进而采用SCE-UA参数优化算法分别优化土壤质地和土壤水力参数,分析不同优化策略对土壤水分模拟结果的影响。研究结果表明,浅层土壤水分对土壤质地较为敏感,敏感性系数达到了0.45以上,并且砂土含量对土壤水分的影响更为显著;利用SCE-UA算法优化土壤质地或土壤水力参数都可以有效地提高土壤水分的模拟精度,优化土壤水力参数易产生"异参同效"现象,而优化土壤质地能够使土壤水力参数的取值范围更加合理。     

河西走廊荒漠区植物生长与水分变化关系分析

为了分析荒漠化防治中荒漠植物生长与降水、土壤水和地下水的关系,在河西走廊荒漠区建立了荒漠化综合防治试验站进行长期定位监测,取得了降水、土壤水、地下水、植物盖度、生物量等数据,采用特征参数算法、相关和逐步多元回归方法,对植物生长和水分的年内、年际变化特征及相关回归模型进行了分析.结果表明：2006-2014年际变化上,土壤水变化最剧烈,降水、生物量、盖度变化剧烈程度极接近,且也较大,地下水位变化最缓和.盖度呈波动性增大趋势较明显,生物量略有增加趋势,降水、土壤水、地下水位变化呈波动性略有降低趋势,但不明显.在植物生长季的3-11月份期间,土壤各层含水率变化步调基本一致,生物量和盖度变化步调基本一致,降水量、地下水埋深变化步调基本一致,年内变化幅度从大到小依次为降水量 > 地下水埋深 > 生物量 > 平均盖度 > 土壤质量含水率.盖度、生物量模型均通过了R拟合检验、F方差检验、t回归系数检验,通过模型可预测变差的58.0%、98.7%,准确率可达52.0%、86.2%.研究成果可为荒漠化防治中的水资源管理以及退耕还林、天然林保护、黑河流域综合治理等工程对水资源影响评估等提供科技支撑和参考数据.     

Description of dynamics of the Tuzla Landslide and its implications for further landslides in the northern slope and shelf of the Cinarcik Basin (Marmara Sea, Turkey)

Seismic and multi-beam bathymetric data from the northern shelf and slope of the Cinarcik Basin, which is generated by the North Anatolian Fault Zone (NAFZ) located in the easternmost basin in the Marmara Sea, were re-interpreted to better understand the future sub-marine landslide susceptibility. Seismic data indicate that upper surface of the sub-marine extension of the Paleozoic rocks has an NNE–SSW oriented basin and a ridge type morphology controlled by the secondary faults of the NAFZ. Basins are fulfilled by Plio-Quaternary sediments, which are cut by strike-slip faults on the shelf and slope. The thickness of basin deposits reaches up to 130 m toward the linear northern slope of the Cinarcik Basin. A relatively recent sub-marine landslide, the Tuzla Landslide, cuts the slope of the Cinarcik Basin. The detailed morphological investigation indicates that the Tuzla Landslide is a deep-seated rotational landslide, which was likely triggered by activity of the NAFZ. Morphological analyses also indicate that the thick Plio-Quaternary deposits on the Paleozoic basement slid during the Tuzla Landslide event. This landslide is considered as a key event to understand the dynamics of the potential landslides on the northern shelf and slope of the Cinarcik Basin. Two areas locating on the eastern and the western sides of the Tuzla Landslide are considered as the potential areas for future sliding due to similarities of geological and geomorphological features with the Tuzla Landslide such as similar thick Plio-Quaternary deposits, similar slope morphology, and similar fault activity cutting the sediments. Considering this information, the purposes of the present study are to determine the dynamics of the possible landslide areas and to discuss their effects on the sub-marine morphology. In the light of the interpretations, the amounts of possible displaced material are obtained. Three different landslide scenarios due to possible slide surfaces for future landslides are developed and assessed. The first scenario is sliding of the sediments at the shelf break. The third scenario is a mass movement of almost whole basin deposits on the Paleozoic rocks. The latter one is evaluated as less important because of the volume of the displaced material, and the latter one is accepted as lowest possible event. Among the scenarios, the second scenario is accepted as the most critical and possible because of the amount of the slipped material and existence of faults rupture, which is considered as further sliding surfaces. These landslides will result in important changes in shelf, slope and basin floor in the study area.     

Analysis and remedies of landslides of cut slopes due to the presence of weak cohesive layers within stronger formations

 Several cases of instability of cut slopes along major highways in Jordan were reviewed in this study, in some detail. Emphasis was placed on the Amman-Irbid highway, but some cases along the Na'ur-Dead Sea highway were also reviewed, with the aim of establishing a wider database of case-studies and examining all possible mechanisms and factors influencing stability. The study showed that major cut slope failures were caused by the presence of weak cohesive layers (mainly clayey marl) interbedded within mostly stronger formations, in addition to the steep cutting angles and unfavorable dip of strata combined with relatively high piezometric surface brought about by poor surface and subsurface drainage. No remedies were implemented to stabilize major cut slope failures (at km 39+200, 44+300, and 56+400) along the Irbid-Jerash-Amman highway. The three major cut slope failures require extensive remedial work and probably advanced geotechnology, which is expected to be expensive. To investigate the influence of various parameters on slope stability, several analyses were performed in addition to back analyses to determine shear strength parameters; parametric sensitivity studies were also performed on some cases. Data was obtained from previous investigations by local and international firms and were screened and modified where needed before being used in stability analyses. Considerable difference between back analysis and test result values for shear strength parameters were observed in many cases. Failure surfaces and mechanisms were accurately depicted in most cases, allowing back analyses to be performed with considerable confidence. The effective residual shear strength parameters for clayey marl needed for stability analysis were found to be: c _r ′=5–18 kPa, and φ _r ′=13°–18°. The relation between total annual rainfall and occurrence of landslides was investigated; it was shown that all landslides occurred in years of very high rainfall, with values always exceeding 400 mm. The probability of exceeding the average total annual rainfall was found to be approximately 0.42 for the three gauging stations considered. Received: 28 October 1996 · Accepted: 23 September 1997     

Interpretation of radon anomalies in seismotectonic and tectonic-gravitational settings: the south-eastern Crati graben (Northern Calabria, Italy)

The study area is located in the south-eastern part of the Crati valley (Northern Calabria, Italy), which is a graben bordered by N–S trending normal faults and crossed by NW–SE normal left-lateral faults. Numerous severe crustal earthquakes have affected the area in historical time. Present-day seismic activity is mainly related to the N–S faults located along the eastern border of the graben. In this area, much seismically induced deep-seated deformation has also been recognised.In the present paper, radon concentrations in soil gas have been measured and compared with (a) lithology, (b) Quaternary faults, (c) historical and instrumental seismicity, and (d) deep-seated deformation.The results highlight the following:

(a) There is no evidence of a strong correlation between lithology and the radon anomalies.

(b) A clear correlation between the N–S geometry of radon anomalies and the orientation of main fault systems has been recognised, except in the southernmost part of the area, where the radon concentrations are strongly affected by the superposition of the N–S and the NW–SE fault systems.

(c) Epicentral zones of instrumental and historical earthquakes correspond to the highest values of radon concentrations, probably indicating recent activated fault segments. In particular, high radon values occur in the zones struck by earthquakes in 1835, 1854, and 1870.

(d) Deep-seated gravitational deformation generally coincides with zones characterised by low radon concentrations.

In the studied area, the anisotropic distribution of radon concentrations is congruent with the presence of neotectonic features and deep-seated gravitational phenomena. The method used in this study could profitably contribute towards either seismic risk or deep-seated gravitational deformation analyses.