A strong motion network in northern Italy: detection capabilities and first analysis

The necessity of a dense network in Northern Italy started from the lack of available data after the occurrence of the 24th November 2004, Ml 5.2, Salò earthquake. Since 2006, many efforts have been made by the INGV (Italian National Institute for Geophysic and Vulcanology), Department of Milano-Pavia (hereinafter INGV MI-PV), to improve the strong-motion monitoring of the Northern Italy regions. This activity led to the installation of a strong-motion network composed by 20 accelerometers, 4 coupled with 20-bits Lennartz Mars88 recorders, 12 coupled with 24-bits Reftek 130 recorders and 4 coupled with 24-bits Gaia2 recorders. The network allow us to reduce, in the area under study, the average inter-distances between strong-motion stations from about 40 km (at November 2004) to 15 km. At present the network includes nine 6-channels stations where velocity sensors work together the strong-motion ones. The data transmission is assured by modem-gsm, with the exception of four stations that send data in real time through a TCP/IP protocol. In order to evaluate different site responses, the stations have been installed both in free field and near (or inside) public buildings, located in the center of small villages. From June 2006 to December 2008 a dataset of 94 events with local magnitude range from 0.7 to 5.1 has been collected. An ad hoc data-processing system have been created in order to provide, after each recorded event, engineering parameters such as peak ground acceleration (PGA) and velocity (PGV), response spectra (SA and PSV), Arias and Housner intensities. Data dissemination is achieved through the web site , while the waveforms are distributed through the Italian strong motion database ().     

On the combination of global and local data in collocation theory

Due to the successful operation of dedicated satellite gravity missions, nowadays high-accuracy global gravity field models have become available. This triggers the challenge to optimally combine this long to medium wavelength gravity field information derived from space-borne data with high-resolution terrestrial gravity data. In this paper, the least squares collocation concept is revised with the attempt to consistently unify the combination procedure in such a way that the full information contained in both data sets is merged. For example, in local or regional geoid determination the remove-restore method is usually applied only partially taking into account the accuracy of the global model coefficients used for the long-wavelength reduction. The key advantage of the extended formulation is the fact that it automatically accounts for the error covariance of all data types involved. The applicability, feasibility and performance of the proposed method is investigated in the frame of numerical closed-loop simulations. The two main fields of application, i.e., the improvement of a global gravity field model by terrestrial gravity field data, and, vice versa, the support to a regional geoid solution by the incorporation of a global gravity field model, have been analyzed and assessed. Although applied under simplified conditions, it could be shown that the method works and is practically applicable.     

Learning and local competitiveness: the case of Turin

This contribution aims to illustrate the most recent initiatives of cluster strategy analysis and implementation to revitalise the Turin metropolitan region. In the paper, theoretical and methodological, analytical and political assumptions interweave inextricably. For these reasons, it is divided into a number of distinct but sequential parts. First of all, the problem of regional competitive advantage and the underlying logic of interpretation are established as the expression of the structural dynamics that involve the contemporary economy.The quantitative and qualitative methodologies that were used to outline the existence of clustered business systems in the Turin region are then examined. More particularly, the Turin manufacturing system has been broken down into eight clusters of three different types: (a) strategic, (b) innovative, (c) traditional. Starting from the clusters identified, I then try to grasp the logic of interpretation of the Turin system and, as a consequence, the strategies of political intervention.Finally, this contribution examines the problems of implementing an industrial policy strategy, which is centred on the creation of `Cluster Observatories', the reorganisation of the local economic and urban planning offices, and the establishment of a special agency for industrial policy.     

On the seismic performance of straight integral abutment bridges: From advanced numerical modelling to a practice-oriented analysis method

The seismic performance of integral abutment bridges (IABs) is affected by the interaction with the surrounding soil, and specifically by the development of interaction forces in the embankment-abutment and soil-piles systems. In principle, these effects could be evaluated by means of highly demanding numerical computations that, however, can be carried out only for detailed studies of specific cases. By contrast, a low-demanding analysis method is needed for a design-oriented assessment of the longitudinal seismic performance of IABs. To this purpose, the present paper describes a design technique in which the frequency- and amplitude-dependency of the soil-structure interaction is modelled in a simplified manner. Specifically, the method consists of a time-domain analysis of a simplified soil-bridge model, in which soil-structure interaction is simulated by means of distributed nonlinear springs connecting a free-field ground response analysis model to the structural system. The results of this simplified method are validated against the results of advanced numerical analyses, considering different seismic scenarios. In its present state of development, the proposed simplified nonlinear model can be used for an efficient evaluation of the longitudinal response of straight IABs and can constitute a starting point for a prospective generalisation to three-dimensional response.     

Analysing the influence of upslope bedrock outcrops on shallow landsliding

A model for the prediction of topographic and climatic control on shallow landsliding in mountainous terrain is enhanced to analyse the impact of upslope rocky outcrops on downslope shallow landsliding. The model uses a ‘generalised quasi-dynamic wetness index’ to describe runoff propagation on bare rock surfaces connected to downslope soil-mantled topographic elements. This approach yields a simple enhanced model capable of describing the influence of upslope bedrock outcrops on the pattern of downslope soil saturation. The model is applied in both diagnostic and predictive modes to a small catchment in the eastern Italian Alps for which a detailed inventory of shallow landslides in areas dominated by rocky outcrops is available. In the diagnostic mode, the model is used with satisfactory results to reproduce the pattern of instability generated by an intense short-duration storm occurred on 14 September 1994, which triggered a large percentage of the surveyed landslides. In the predictive mode, the model is used for hazard assessment, and the return time of the critical rainfall needed to cause instability for each topographic element is determined. Modelling results obtained in the predictive mode are evaluated against all the surveyed landslides. It is revealed that the generalised quasi-dynamic model offers considerable improvement over the non-generalised quasi-dynamic model and the steady-state model in predicting existing landslides as represented in the considered landslide inventory.     

基于多尺度数字地形定量分析的月球线性构造自动提取研究

月球表面构造对于理解和重建月球地质构造演化具有重要意义,月岭、月溪等线性构造的形态及分布特征与月球内动力构造运动密切相关。极为有限的样品和难度极高的野外勘察使得遥感成为行星科学研究的最主要手段。中国、美国、日本、印度等国先后发射的多颗新型探月卫星获取了大量高质量数据,尤其是高分辨率的数字地形数据(DTM,Digital Terrain Model)。高分辨率的DTM为月球表面构造特征的自动提取带来了新的机遇与挑战。文中利用多种分辨率的DTM数据,基于多尺度数字地形定量分析方法,识别和提取月球表面的线性构造。使用的地形数据包括500 m分辨率“嫦娥一号”激光高度计数据,100 m分辨率LRO-WAC广角相机数据,60 m分辨率的LRO-LOLA激光测距仪数据以及分辨率高达5 m的LRO-NAC窄视角相机数据。文中使用地形曲率来识别月溪月岭等线性构造,并利用不同滑动窗口大小和阈值进行线性构造的自动提取。对研究区试验结果的定量分析表明,文中提出的基于地形曲率的月表线性构造自动提取方法是有效且可行的,其结果可为月球表面线性构造解译提供重要参考,提高构造解译时效性和精度。     

An accurate strength amplification factor for the design of SDOF systems with P–Δ effects

The response of structures subjected to seismic actions is always influenced by P–Δ effects. The importance of this effect is generally modest for structures experiencing an elastic response but often relevant for structures responding well within the inelastic range of behaviour. Seismic codes indicate that P–Δ effects may be counterbalanced through an increase in the structural strength required by a first order analysis. This increase is calculated by means of a strength amplification factor. The expressions suggested in codes for this factor are simplistic and often criticized by researchers. In this paper, the effectiveness of some of the provisions reported in the literature or suggested in seismic codes is evaluated on single degree of freedom systems with different periods of vibration. As suggested by past studies, attention is focused on the influence of the interstorey drift sensitivity coefficient, significant duration of the ground motion, class of the site soil, displacement ductility and equivalent viscous damping ratio of the system. Finally, an accurate expression of the strength amplification factor is proposed. Copyright © 2013 John Wiley & Sons, Ltd.     

A two‐step direct method for estimating the seismic response of nonlinear structures equipped with nonlinear viscous dampers

The insertion of fluid viscous dampers in building structures is an innovative technology that can improve significantly the seismic response. These devices could be very useful also in the retrofit of existing buildings. The effect of this typology of damping system is usually identified with an equivalent supplemental damping ratio, which depends on the maximum displacement of the structure, so that iterative procedures are required. In this paper, a simplified direct assessment method for nonlinear structures equipped with nonlinear fluid viscous dampers is proposed. The method proposed in this study is composed by two steps. The first one yields the direct estimate of the supplemental damping ratio provided by nonlinear viscous dampers in presence of a linear elastic structural response. The second step extends the procedure to structures with nonlinear behavior. Both graphical and analytical approaches have been developed. The proposed method has then been verified through several applications and comparisons with nonlinear dynamic analyses. Moreover, an investigation has been performed with regard to the influence of the relations that define the damping reduction factor and the hysteretic damping. Copyright © 2014 John Wiley & Sons, Ltd.     

Influence of root characteristics and soil variables on the uprooting mechanics of Avena sativa and Medicago sativa seedlings

The success of seedlings and rejuvenated woody debris growing on river bedforms depends on the resistance to uprooting by flow provided by their simple root architecture. Avena sativa and Medicago sativa seedlings were used in flume experiments as prototypes for juvenile riparian plants. Very little is known about the magnitude of root anchoring forces and the role of secondary roots of such simple root systems. We performed 1550 vertical uprooting experiments on Avena sativa and Medicago sativa seedlings grown in quartz sand. Seedlings were pulled up by direct traction using a wheel driven by a computer‐controlled motor and the force was recorded. Roots were scanned and architectural parameters (root length and number of roots) determined. Uprooting force and work (the integral of the applied force times the distance over which it is applied) were then related to root architecture and soil variables. Resistance to uprooting increased with decreasing sediment size and sediment moisture content. The initial response of the root–soil system to uprooting showed linear elastic behaviour with modulus increasing with plant age. While the maximum uprooting force was found to increase linearly with total root length and be mainly dependent on the length of the main root, uprooting work followed a power law and has to be related to the whole root system. Thus, for the young plants we considered, secondary roots are responsible for the ability to withstand environmental disturbances in terms of duration rather than magnitude. This distinction between primary and secondary roots can be of crucial importance for seedlings of riparian species germinating on river bars and islands where inundation is a main cause of mortality. Beyond clarifying the biomechanical role of soil and root variables, the uprooting statistics obtained are useful in interpreting and designing ecomorphodynamic flume experiments. Copyright © 2014 John Wiley & Sons, Ltd.     

Modelling habitat requirements of bullhead (Cottus gobio) in Alpine streams

In the context of water resources planning and management, the prediction of fish distribution related to habitat characteristics is fundamental for the definition of environmental flows and habitat restoration measures. In particular, threatened and endemic fish species should be the targets of biodiversity safeguard and wildlife conservation actions. The recently developed meso-scale habitat model (MesoHABSIM) can provide solutions in this sense by using multivariate statistical techniques to predict fish species distribution and to define habitat suitability criteria. In this research, Random Forests (RF) and Logistic Regressions (LR) models were used to predict the distribution of bullhead (Cottus gobio) as a function of habitat conditions. In ten reference streams of the Alps (NW Italy), 95 mesohabitats were sampled for hydro-morphologic and biological parameters, and RF and LR were used to distinguish between absence/presence and presence/abundance of fish. The obtained models were compared on the basis of their performances (model accuracy, sensitivity, specificity, Cohen’s kappa and area under ROC curve). Results indicate that RF outperformed LR, for both absence/presence (RF: 84 % accuracy, k = 0.58 and AUC = 0.88; LR: 78 % accuracy, k = 0.54 and AUC = 0.85) and presence/abundance models (RF: 79 % accuracy, k = 0.57 and AUC = 0.87; LR: 69 % accuracy, k = 0.43 and AUC = 0.81). The most important variables, selected in each model, are discussed and compared to the available literature. Lastly, results from models’ application in regulated sites are presented to show the possible use of RF in predicting habitat availability for fish in Alpine streams.