Influence of sample and terrain unit on landslide susceptibility assessment at La Pobla de Lillet,Eastern Pyrenees,Spain

The reliability of susceptibility maps depends largely on the quality of the information used for its evaluation. This study seeks to analyze the influence of sample size and type on the results of discriminant analysis applied to shallow landslide susceptibility assessment. The study also assesses the role of the terrain unit in discriminant analysis. To this end, two databases based on fieldwork (slope unit) and GIS with 15- and 45-m grid cells (grid cell-based unit), were compared in the same zone at La Pobla de Lillet, Spanish Eastern Pyrenees. The results show that although there is no significant influence of the type of sample, it is necessary to use at least half of the individuals of the sample in order to obtain good results from discriminant analysis. It is the terrain unit that exerts the biggest influence on the result of susceptibility. Some morphometric parameters related to landslides were compared in the databases. The slope unit of the fieldwork database better reflects the land characteristics than the regular grid used by GIS. The values of the variables obtained by GIS procedures are smooth, obtaining mean errors for the slope angle variable of 19.5 and 33.5% for the grids of 15 and 45 m, respectively, in the study area. One-way and T tests demonstrate that the smoothness of the values exerts a decisive influence on the discriminant results. Kappa’s analysis shows that there is no significant equivalence between some of the categorical variables used in both databases. The use of these variables demand the application of clearly defined criteria. The cell size should match the dimensions of the phenomenon analyzed given the unsuitability of the grid of 45 m in this study.     

Sensitivity of the Calculated <Emphasis Type="Italic">g</Emphasis>-Mode Frequencies to Pulsation Codes and their Parameters

From the recent work of the Evolution and Seismic Tools Activity (ESTA: Monteiro et al., ESA, SP-1306, 363 – 371, 2006 and Lebreton et al., Astrophys. Space Sci. 316, 1 – 12, 2008), whose Task 2 is devoted to comparing pulsational frequencies computed using most of the pulsational codes available in the asteroseismic community, the dependence of the theoretical frequencies on non-physical choices is now quite well specified. To ensure that the accuracy of the computed frequencies is of the same order of magnitude or better than the observational errors, some requirements in the equilibrium models and the numerical resolutions of the pulsational equations must be followed. In particular, we have verified the numerical accuracy obtained with the Saclay seismic model, which is used to study the solar g-mode region (60 to 140 μHz). We have compared the results coming from the Aarhus adiabatic pulsation code (ADIPLS), with the frequencies computed with the Granada Code (GraCo) taking into account several possible non-physical choices and the effect of using two different outer mechanical boundary conditions. We have concluded that the present equilibrium models and the use of the Richardson extrapolation ensure an accuracy of the order of 0.01 μHz in the determination of the frequencies, which is quite enough for our purposes.     

Granada oscillation code (GraCo)

Granada oscillation code (GraCo) is a software constructed to compute adiabatic and non-adiabatic oscillation eigenfunctions and eigenvalues. The adiabatic version gives the standard numerical resolution, and also the Richardson extrapolation, different sets of eigenfunctions, different outer mechanical boundary conditions or different integration variables. The non-adiabatic version can include the atmosphere-pulsation interaction. The code has been used for intensive studies of δ Scuti, γ Doradus, β Ceph., SdO and, SdB stars. The non adiabatic observables “phase-lag” (the phase between the effective temperature variations and the radial displacement) and ${\delta T_{\mathrm{eff}}\over T_{\mathrm{eff}}}$ (relative surface temperature variation) can help to the modal identification. These quantities together with the energy balance (“growth rate”) provide useful additional information to the adiabatic resolution (eigenfrequencies and eigenfunctions).     

A review of assessing landslide frequency for hazard zoning purposes

The probability of occurrence is one of the key components of the risk equation. To assess this probability in landslide risk analysis, two different approaches have been traditionally used. In the first one, the occurrence of landslides is obtained by computing the probability of failure of a slope (or the reactivation of existing landslides). In the second one, which is the objective of this paper, the probability is obtained by means of the statistical analysis of past landslide events, specifically by the assessment of the past landslide frequency. In its turn, the temporal frequency of landslides may be determined based on the occurrence of landslides or from the recurrence of the landslide triggering events over a regional extent. Hazard assessment using frequency of landslides, which may be taken either individually or collectively, requires complete records of landslide events, which is difficult in some areas. Its main advantage is that it may be easily implemented for zoning. Frequency assessed from the recurrence of landslide triggers, does not require landslide series but it is necessary to establish reliable relations between the trigger, its magnitude and the occurrence of the landslides. The frequency of the landslide triggers can be directly used for landslide zoning. However, because it does not provide information on the spatial distribution of the potential landslides, it has to be combined with landslide susceptibility (spatial probability analysis) to perform landslide hazard zoning. Both the scale of work and availability of data affect the results of the landslide frequency and restrict the spatial resolution of frequency zoning as well. Magnitude–frequency relationships are fundamental elements for the quantitative assessment of both hazard and risk.     

Rockfalls: analysis of the block fragmentation through field experiments

Landslides - Fragmentation is a common feature of rockfall that exerts a strong control on the trajectories of the generated blocks, the impact energies, and the runout. In this paper, we present a...     

Researching European 'alternative' food networks: some methodological considerations

Recent European literature on 'alternative' food networks (AFNs) draws heavily upon an apparently accessible and diverse body of non-conventional food networks in the agro-food sector and whilst researchers frequently refer to individual examples of farmers markets, box schemes, producer cooperatives and community-supported agriculture projects, less attention is given to the methodological processes that facilitate the identification and examination of these networks. From the preliminary stages of a research project focusing on examples of AFNs, ² this paper examines the process of operationalizing AFNs research and reviews the difficulties associated with identifying, comparing and characterizing AFNs.     

Empirical evaluation of site effects in the metropolitan area of San José, Costa Rica

Site effects for 11 selected locations were determined in the capital city of Costa Rica. We used a strong motion network made of eight K2 and three SSA accelerographs. The network recorded more than 60 earthquakes in the magnitude range from 2 to 5 during a period of nine months. The site effects were determined using the sediment-to-bedrock spectral ratio (SBSR) and the horizontal-to-vertical spectral ratio (HVSR) techniques and a time window 4 s beginning from the S-wave arrival. The result suggests that the amplification in the capital city is to be in the range from 2.0 to 3.0. The fundamental frequencies were found to be high in the southern and eastern part of the study area and low in the northern and western part. A possible topographic effect was also observed for one of the stations located nearby a river canyon. The results from earthquake data were compared with the ones obtained from noise data. The horizontal-to-vertical noise ratio (HVNR) technique was used to estimate the site effects using ambient noise. The fundamental frequencies were found to correlate very well between both sets of data; on the other hand, the amplitude given by the noise was observed to be always lower than the one derived from the earthquake data.     

Post-fire management effects on sediment (dis)connectivity in Mediterranean forest ecosystems: Channel and catchment response

Forest fires and post-fire practices influence sediment connectivity (SC). In this study, we use the ‘aggregated index of connectivity’ (AIC) to assess SC in five Mediterranean catchments (198–1090 ha) affected by a wildfire in 2012 in south-eastern Spain. Two temporal scenarios were considered, immediately after the fire and before post-fire management, and 2 years after the fire including all practices (hillslope barriers, check-dams, afforestation, salvage logging and skid trails). One LiDAR (light detection and ranging)-derived digital elevation model (DEM, 2 m × 2 m resolution) was generated, per scenario. The five catchment outlets were established as the computation target (AIC_OUT), and structural and functional SC were calculated. Index outputs were normalized to make the results of the non-nested catchments comparable (AIC_N-OUT). The output analysis includes the SC distribution along the catchments and at local scale (929 sub-catchments, 677 in the burned area), the hillslope and channel measures' effect on SC, and a sedimentological analysis using observed area-specific sediment yield (SSY) at 10 new (built after post-fire practices) concrete check-dams located in the catchments (SSY = 1.94 Mg ha⁻¹ yr⁻¹; σ = 1.22). The catchments with more circular shapes and steeper slopes were those with higher AIC_N-OUT. The structural SC maps – removing the rainfall erosivity influence – allowed evaluating the actual role played by the post-fire practices that reduced SC ( $\overline{x}$= − 1.19%; σ = 0.41); while functional SC was linked to the actual change of SC ( $\overline{x}$= + 5.32%; σ = 0.62). Hillslope treatments resulted in significant changes on AIC_N-OUT at sub-catchment scale with certain disconnectivity. A good and positive correlation was found between the SSY and the changes of AIC_N-OUT. However, the coarse DEM resolution explained the lack of effect of the rock check-dams – located on the secondary channels – on AIC_N-OUT. AIC_N-OUT proved to be a useful tool for decision making in post-fire restoration, but an optimal input data is still necessary to refine calculations.