Slope dynamics of Lake Albano (Rome,Italy): insights from high resolution bathymetry

New detailed data about the morphology of the submerged slopes of Lake Albano (Rome, Italy) have been collected by a sonar multibeam survey financed by the Italian Department of Civil Protection. These data allow for investigation of the subaqueous slope dynamics of the lake, which partially fills a volcanic depression, and the elucidation of the relationships between subaqueous and subaerial slope processes. Subaerial, submerged and combined subaerial/submerged landslide‐related morphologies were detected around the inner slopes of the lake. In the submerged slopes, several gravity‐induced landforms were recognized: landslide scar areas, landslide accumulations, erosional chutes and channels, block fields, isolated blocks, scarps and slope breaks. An attempt to evaluate the state of activity of the submerged slopes was carried out by taking into consideration the relative freshness of some selected landforms. Interpretation of bathymetric data, as well as direct surveys of the subaerial slopes, was used to assess the morphometric features and interpret the type of movement of the landslides. We propose a comprehensive classification based on the landslide's size and type of movement. We recognized rock fall/topples, debris flows, rock slides and slump, complex rock slides/channelled flows and debris slide and slump. The volume of the main landslides ranged between 10¹ and 10³ m³, while a few rock and debris slides have volumes ranging between 10³ and 10⁵ m³. Two large palaeo‐landslides with volumes on the order of 10⁶ m³ were identified in the southern and northern part of the lake, respectively. Velocities of the recognized landslides range from rapid to extremely rapid. Two main landslide hazard scenarios have been depicted from the results of the integrated analysis of both subaerial and submerged gravity‐induced landforms. The most hazardous scenario involves extremely rapid large volume events (>10⁶ m³) that could, if they interacted with water, induce catastrophic tsunamis. Copyright © 2009 John Wiley & Sons, Ltd.     

永登黄土地区爆破地震动近场效应的研究

一.前言不同场地条件下的强震记录,不仅对开展地震地面运动研究很重要,而且对地震工程和工程抗震等方面的研究也极为重要。但是,由于破坏性地震发生的机率及当前地震预报的水平所限,要取得理想的强震记录很困难,尤其是取得主震的近场记录更为困难。因此利用人工手段模拟天然地震,从而取得强震地面运动的各种资料,是一种比较好的办法。虽然人工地     

Empirical attenuation relationship for Arias Intensity

Arias Intensity is a ground motion parameter that captures the potential destructiveness of an earthquake as the integral of the square of the acceleration–time history. It correlates well with several commonly used demand measures of structural performance, liquefaction, and seismic slope stability. A new empirical relationship is developed to estimate Arias Intensity as a function of magnitude, distance, fault mechanism, and site category based on 1208 recorded ground motion data from 75 earthquakes in active plate‐margins. Its functional form is derived from the point‐source model, and the coefficients are determined through non‐linear regression analyses using a random‐effects model. The results show that for large magnitude earthquakes (M > 7) Arias Intensity was significantly overestimated by previous relationships while it was underestimated for smaller magnitude events (M ? 6). The average horizontal Arias Intensity is not significantly affected by forward rupture directivity in the near‐fault region. The aleatory variability associated with Arias Intensity is larger than that of most other ground motion parameters such as spectral acceleration. However, it may be useful in assessing the potential seismic performance of stiff engineering systems whose response is dominated by the short‐period characteristics of ground motions. Copyright © 2003 John Wiley & Sons, Ltd.     

地震动强度参数相关性对地震滑坡危险性影响分析

本文基于全概率地震滑坡危险性分析方法,利用蒙特卡罗模拟研究在不同临界屈服加速度a_c、永久位移模型、场地类别和断层距情况下,地震动强度参数相关性对地震滑坡危险性结果的影响规律。主要结果表明:在进行滑坡危险性分析时,不考虑多地震动强度参数相关性会造成预测位移值偏小,滑坡风险被低估。因此,考虑地震动强度参数相关性对滑坡危险性评价很有必要,这能使预测结果反映地震动参数样本作为输入时的实际相关性特征,为合理进行滑坡防护提供理论依据和参考。     

APPLICATION OF TWO SIMPLIFIED NEWMARK MODELS TO THE ASSESSMENT OF LANDSLIDES TRIGGERED BY THE 2008 WENCHUAN EARTHQUAKE

At present, with the wide application of the Newmark method, various Newmark empirical formulas with different ground motion parameters have been fitted by many researchers based on global strong-motion records. However, the existing study about the Wenchuan earthquake does not quantitatively evaluate the applicability of different Newmark models based on the actual landslides distribution. The aim of this paper is to present a comparison between observed landslides from the 2008 Wenchuan earthquake and predicted landslides using Newmark displacement method based on different ground motion parameters. The factor-of-safety map and critical acceleration(a_c)map in the study area are obtained by using the terrain data and geological data. The distribution of Arias intensity(I_a)and PGA in the study area is obtained by using the attenuation formulas of Arias intensity(I_a)and PGA, which is regressed by Wenchuan ground motion records. Based on the distribution of Arias intensity(I_a)and PGA parameters, we obtained the predicted locations of landslide using Newmark regression equations which are generated using global strong-motion records. The results shows that the assessment results can better reflect the macroscopic distribution characteristics of co-seismic landslides, most predicted landslide cells are distributed on the two sides of the Beichuan-Yingxiu Fault, especially the Pengguan complex rock mass in the hanging wall. The abilities to predict landslide occurrence of the two Newmark simplified models are different. On the whole, the evaluated result of simplified model based on parameter I_a is better than that based on PGA parameter. The GFC values obtained by the Newmark model of I_a and PGA parameters are 65.7% and 34.9%respectively. The evaluated result based on I_a can better reflect the macro distribution of coseismic landslides. The Ls_Pred value based on the Newmark model of parameter I_a is 26.5%, and the Ls_Pred value based on the Newmark model of PGA parameter is 10.3%. However the total area of predicted landslides accounts for 2.4% of the study area, which indicates that the predicted landslide cells are greater than the observed landslide cells. This reminds us that depending on the current input of shear strength and ground-motion parameters, we can only conduct landslide hazard assessment in macro areas, the ability to predict landslide can be improved using more accurate topographic data and input parameters.     

Experimental study of debris flow caused by domino failures of landslide dams

The formation of landslide dams is often induced by earthquakes in mountainous areas.The failure of a landslide dam typically results in catastrophic flash floods or debris flows downstream.Significant attention has been given to the processes and mechanisms involved in the failure of individual landslide dams.However,the processes leading to domino failures of multiple landslide dams remain unclear.In this study,experimental tests were carried out to investigate the domino failure of landslide dams and the consequent enlargement of downstream debris flows.Different blockage conditions were considered,including complete blockage,partial blockage and erodible bed（no blockage）.The mean velocity of the flow front was estimated by videos.Total stress transducers（TSTs）and Laser range finders（LRFs） were employed to measure the total stress and the depth of the flow front,respectively.Under a complete blockage pattern,a portion of the debris flow was trapped in front of each retained landslide dam before the latter collapsed completely.This was accompanied by a dramatic decrease in the mean velocity of the flow front.Conversely,under both partial blockage and erodible bed conditions,the mean velocity of the flow front increased gradually downward along the sloping channel.Domino failures of the landslide dams were triggered when a series of dams（complete blockage and partial blockage） were distributed along the flume.However,not all of these domino failures led to enlarged debris flows.The modes of dam failures have significant impacts on the enlargement of debris flows.Therefore,further research is necessary to understand the mechanisms of domino failures of landslide dams and their effects on the enlargement of debris flows.     

Large landslides and their effect on sediment flux in South Westland,New Zealand

Landslides and runoff are dominant erosional agents in the tectonically active alpine South Westland area of New Zealand, characterized by high uplift rates and extreme orographic precipitation. Despite a high density of shallow debris slides and flows, the geomorphic imprints of deep‐seated bedrock failures are dominant and persistent. Over 50 large (>1 km²) landslides comprising rock slide[sol ]avalanches, complex rotational and rock‐block slides, wedge failures, and deep‐seated gravitational slope deformation were detected on air photos and shaded‐relief images. Major long‐term impacts on alpine rivers include (1) forced alluviation upstream of landslide dams, (2) occlusion of gorges and triggering of secondary riparian landslides, and (3) diversion of channels around deposits to form incised meandering gorges. Remnants of large prehistoric (i.e. pre‐1840) landslide deposits possibly represent the low‐frequency (in terms of total area affected yet dominant) end of the spectrum of mass wasting in the western Southern Alps. This is at odds with high erosion rates in an active erosional landscape. Large landslides appear to have dual roles of supplying and retaining sediment. The implications of these roles are that (1) previous models of (shallow) landslide‐derived sediment flux need to be recalibrated, and (2) geomorphic effects of earthquake‐induced landsliding may persist for at least 10² years. Copyright © 2005 John Wiley & Sons, Ltd.     

拟合多阻尼比目标反应谱的高精度地震动调整方法

基于地震动调整效果的衡量指标比较了时域合成法和时频分析法的优缺点,在推导阿里亚斯强度与绝对加速度反应谱定量关系的基础上,将时域叠加小波函数法和时频小波分析调整法相结合,提出了一种能保留地震动强非平稳特性、对真实地震动相位差谱改动较少、能同时拟合多阻尼比目标反应谱的高精度地震动调整方法,并通过拟合美国规范D-V-A联合谱的算例证明了该方法的精度和通用性。     

Evolution of the north flank of Tenerife by recurrent giant landslides

Geomorphologic analysis of submarine and subaerial surface features using a combined topographic/bathymetric digital elevation model coupled with onshore geological and geophysical data constrain the age and geometry of giant landslides affecting the north flank of Tenerife. Shaded relief and contour maps, and topographic profiles of the submarine north flank, permit the identification of two generations of post-shield landslides. Older landslide materials accumulated near the shore (<40-km) and comprise 700 km³ of debris. Thickening towards a prominent axis suggests one major landslide deposit. Younger landslide materials accumulated 40–70 km offshore and comprise the products of three major landslides: the La Orotava landslide complex, the Icod landslide and the East Dorsal landslide complex, each with an onshore scar, a proximal submarine trough, and a distal deposit lobe. Estimated lobe volumes are 80, 80 and 100 km³, respectively. The old post-shield landslide scar is an amphitheatre, 20–25 km wide, partly submarine, now completely filled with younger materials. Age–width relationships for Tenerife's coastal platform plus onshore geological constraints suggest an age of ca. 3 Ma for the old collapse. Young landslides are all less than 560 ka old. The La Orotava and Icod slides involved failures of slabs of subaerial flank to form the subaerial La Orotava and Icod valleys. Offshore, they excavated troughs by sudden loading and basal erosion of older slide debris. The onshore East Dorsal slide also triggered secondary failure of older debris offshore. The slab-like geometry of young failures was controlled by weak layers, deep drainage channels and flank truncation by marine erosion. The (partly) submarine geometry of the older amphitheatre reflects the absence of these features. Relatively low H/L ratios for the young slides are attributed to filling of the slope break at the base of the submarine edifice by old landslide materials, low aspect ratios of the failed slabs and channelling within troughs. Post-shield landslides on Tenerife correlate with major falls in sea level, reflecting increased rates of volcanism and coastal erosion, and reduced support for the flank. Landslide head zones have strongly influenced the pattern of volcanism on Tenerife, providing sites for major volcanic centres.     

汶川地震诱发滑坡的地震动加速度评判标准

通过对汶川MS8.0地震强震记录资料的计算分析,给出一个与地震诱发滑坡关系比较密切的地震动加速度参数--最大临界加速度.分析表明,最大临界加速度与地震滑坡的相关性高于峰值加速度,而且可以消除峰值加速度作为判据使用时存在的问题.利用汶川地震强震资料建立了该参数在震区的衰减关系,由衰减关系得到的地震滑坡影响区域与汶川地震滑...     

A note on time of maximum response of single degree of freedom oscillator to earthquake excitation

The dependence of the relative time of maximum response of single degree of freedom system, subjected to recorded strong earthquake ground motion, on magnitude, epicentral distance and the Modified Mercalli Intensity at the site has been studied. Two empirical regression models are presented that enable estimation of the relative time of maximum response in terms of (1) earthquake magnitude and epicentral distance, or (2) Modified Mercalli Intensity at the site. The empirical distribution functions of the observed times of maximum response are presented. Both models also consider whether motion is horizontal or vertical, and the effects of the geologic conditions surrounding the site. The results are useful for the response spectrum approach in earthquake resistant design, as they provide guidelines for superposition of different loads in time.     

岷县漳县6.6级地震典型滑坡特征及其诱发机制

地震和降雨是滑坡产生的两大诱因。一般认为二者的耦合作用概率小,在现实中也较少发现有此种实例。岷县漳县6.6级地震中黄土地震滑坡广泛发生,本文通过现场调查,在相关降雨量数据、航空影像空间分析的基础上研究了两个地点(永光村滑坡和堡子村滑坡)的典型地震黄土滑坡的空间展布特征和发生、发展过程,分析了诱发机制。结果发现:(1)地震滑坡呈带状分布与地震发震构造走向一致;(2)位于极震区范围的永光村黄土滑坡具有泥流特征,土体含水量可达塑限以上,是由于过量降水和强地震动耦合作用下发生;(3)堡子村黄土地震滑坡则主要为强地震动所诱发,滑距较短,并具滞后发生特性。本结果对未来地震中滑坡的预防与防治具有借鉴意义。     

仪器烈度计算方法的初步研究

现行中国地震烈度表中,给出了Ⅴ度以上烈度区水平向地面运动峰值加速度（PGA）和峰值速度（PGV）两个物理参数与地震烈度的参考关系。当分别用PGA和PGV计算仪器烈度时,计算结果与现场调查烈度相符率很低。文中提出了基于相符率的加权方案,利用PGA和PGV综合评定烈度。评定结果表明,相符率有较大提高,说明该方法能有效地使仪器烈度更加接近宏观烈度。     

Earthquake-induced landslide displacement attenuation models and application in probabilistic seismic landslide displacement analysis

A landslide displacement (DLL) attenuation model has been developed using spectral intensity and a ratio of critical acceleration coefficient to ground acceleration coefficient. In the development of the model,a New Zealand earthquake record data set with magnitudes ranging from 5.0 to 7.2 within a source distance of 175 km is used. The model can be used to carry out deterministic landslide displacement analysis,and readily extended to carry out probabilistic seismic landslide displacement analysis. DLL attenuation models have also been developed by using earthquake source terms,such as magnitude and source distance,that account for the effects of earthquake faulttype,source type,and site conditions. Sensitivity analyses show that the predicted DLL values from the new models are close to those from the Romeo model that was developed from an Italian earthquake record data set. The proposed models are also applied to an analysis of landslide displacements in the Wenchuan earthquake,and a comparison between the predicted and the observed results shows that the proposed models are reliable,and can be confidently used in mapping landslide potential.     

Establishing a threshold for rainfall-induced landslides by a kinetic energy–duration relationship

Many investigators have attempted to define the threshold of landslide failure, that is, the level of the selected climatic variable above which a rainfall-induced landslide occurs. Intensity–duration (I–d) relationships are the most common type of empirical thresholds proposed in the literature for predicting landslide occurrence induced by rainfall. Recent studies propose the use of the kinetic power per unit volume of rainfall (J m⁻² mm⁻¹) to quantify the threshold of landslides induced by rainfall. In this paper, the relationship between rainfall duration and kinetic power corresponding to landslides triggered by rain was used to propose a new approach to define the threshold for predicting landslide occurrence. In particular, for the first time, a kinetic power per unit volume of rainfall–duration relationship is proposed for defining the minimum threshold needed for landslide failure. This new method can be applied using commonly used relationship for estimating the kinetic power per unit volume of rainfall and a new equation based on the measured raindrop size distribution. The applicability of this last method was tested using the data of rainfall intensity, duration and median volume diameter for 51 landslides in Taiwan. For the 51 landslides, the comparison between the measured pairs' kinetic power–duration and all selected relationships demonstrated that the equation based on the measured raindrop size distribution is the best method to define the landslide occurrence threshold, as it is both a process-oriented approach and is characterized by the best statistical performance. This last method has also the advantage to allow the forecasting of landslide hazard before the end of the rainfall event, since the rainfall kinetic power threshold value can be exceeded for a time interval less than the event duration.     

The Main Features of the Local Geological Conditions Can Explain the Macroseismic Intensity Caused in Xiji-Langfu (Beijing) by the Ms = 7.7 Tangshan 1976 Earthquake

—The special geological conditions in the Xiji-Langfu area are the main reason for the anomalous high macroseismic intensity caused by the Tangshan, 1976 earthquake. The area is formed by deep deposits - mainly alluvium sands and clays poorly consolidated and with high water content - that have been trapped by the Xiadian fault. From simulated ground motion we have computed quantities commonly used for engineering purposes like the acceleration maximum amplitude (AMAX) and the total energy of ground motion (W), which is related to the Arias Intensity. The thick low velocity deposits are responsible for the large increment of the values of AMAX and W inside the basin. On the two sides of the Xiadian fault AMAX and W can vary by 200% and 700% respectively, and these variations are quite stable with varying thickness of the sedimentary deposit used in the models. With the existing relationships between acceleration (AMAX) and macroseismic intensity (I) our results can explain the large values of I observed in the Xiji-Langfu area, in connection with the Tangshan earthquake.     

A method for predicting co-seismic displacements of slopes for landslide hazard zonation

Landslide hazard zonation based on co-seismic slope displacements has been applied in many regions. As there are a large number of slopes to be analyzed and it is impossible to obtain actual acceleration time histories for each of these slopes, the co-seismic displacements are often estimated by some simple empirical formulas, which are derived through regression analysis based on a certain set of acceleration time histories and can only be validly applied to regions similar to where the time history data were recorded. In this paper, treating the ground motion as a random process, a formula for calculating the expected value of Newmark displacement with the acceleration amplitude spectrum as input is derived. Since the formula is theoretically equivalent to the double integration procedure in a rigorous Newmark analysis, which has also been verified by careful comparisons of the calculated results, it can be applied for different regions. By combining the formula with ground motion simulations, a new method for estimating co-seismic slope displacements is proposed. The application of the method in the seriously struck area by Wenchuan earthquake shows that it is an effective tool for predicting co-seismic slope displacements as the predicted landslide distribution by using its estimated results agrees reasonably with the actual observations.     

地形效应影响下地震动参数与斜坡稳定性的相关性研究

地形对地震动的影响比较复杂, 考虑地形放大效应的地震滑坡稳定性分析需要选择合适的地震动参数. 本文使用自贡地形影响台阵记录到的2008年汶川M_S8.0地震主震加速度记录, 分析了地震动峰值加速度、 阿里亚斯烈度以及90%能量持时随地形高度的变化, 探讨了地形效应作用下峰值加速度和阿里亚斯烈度与地震动作用下斜坡稳定性的相关性. 结果表明: ① 地形场地对峰值加速度和阿里亚斯烈度均有显著的放大效应. 地形放大效应较为复杂, 其整体上随台站高度的增加而增大, 水平向的放大效应大于竖直向. 水平向峰值加速度的放大系数为1.1—1.8, 阿里亚斯烈度的放大系数为1.2—3.3; 竖直向相应放大系数分别为1.1—1.3和1.2—1.7. ② 地形对地震动持时也有一定的放大效应, 但不同高度、 不同分量的放大效应没有显著差异, 其放大系数均约为1.3. ③ 阿里亚斯烈度和峰值加速度均能很好地表征地形对地震动的影响, 与地震动对斜坡稳定性的影响具有很强的相关性. 与峰值加速度相比, 阿里亚斯烈度综合了地震动的多方面特征, 可以更好地表征地形对地震动的影响, 与地震动作用下斜坡稳定性的相关性更强.      

New predictive equations for Arias intensity from crustal earthquakes in New Zealand

Arias Intensity (Arias, MIT Press, Cambridge MA, pp 438–483, 1970) is an important measure of the strength of a ground motion, as it is able to simultaneously reflect multiple characteristics of the motion in question. Recently, the effectiveness of Arias Intensity as a predictor of the likelihood of damage to short-period structures has been demonstrated, reinforcing the utility of Arias Intensity for use in both structural and geotechnical applications. In light of this utility, Arias Intensity has begun to be considered as a ground-motion measure suitable for use in probabilistic seismic hazard analysis (PSHA) and earthquake loss estimation. It is therefore timely to develop predictive equations for this ground-motion measure. In this study, a suite of four predictive equations, each using a different functional form, is derived for the prediction of Arias Intensity from crustal earthquakes in New Zealand. The provision of a suite of models is included to allow for epistemic uncertainty to be considered within a PSHA framework. Coefficients are presented for four different horizontal-component definitions for each of the four models. The ground-motion dataset for which the equations are derived include records from New Zealand crustal earthquakes as well as near-field records from worldwide crustal earthquakes. The predictive equations may be used to estimate Arias Intensity for moment magnitudes between 5.1 and 7.5 and for distances (both r_jb and r_rup) up to 300 km.