On the reliability of long‐period response spectral ordinates from digital accelerograms

Using records from co‐located broadband and digital strong motion (SM) instruments, it is first shown that the displacement waveforms obtained by double integration of the accelerogram need not be free of unrealistic baseline drift to yield reliable spectral ordinates up to at least 10 s. Secondly, to provide objective criteria for selecting reliable digital SM records for ground motion predictions at long periods, a set of synthetic accelerograms contaminated by random long‐period noise has been used, and the difference between the original accelerograms and the spurious ones in terms of response spectra has been quantified, by introducing a noise index that can be easily calculated based on the velocity waveform of the record. The results of this study suggest that high‐pass filtering the digital acceleration record from a cutoff period selected to suppress baseline drifts on the displacement waveform appears to be in most cases too conservative and unduly depletes reliable information on long‐period spectral ordinates. Copyright © 2007 John Wiley & Sons, Ltd.     

An automatic procedure to forecast tephra fallout

Tephra fallout constitutes a serious threat to communities around active volcanoes. Reliable short-term forecasts represent a valuable aid for scientists and civil authorities to mitigate the effects of fallout on the surrounding areas during an episode of crisis. We present a platform-independent automatic procedure with the aim to daily forecast transport and deposition of volcanic particles. The procedure builds on a series of programs and interfaces that automate the data flow and the execution and subsequent postprocess of fallout models. Firstly, the procedure downloads regional meteorological forecasts for the area and time interval of interest, filters and converts data from its native format, and runs the CALMET diagnostic model to obtain the wind field and other micro-meteorological variables on a finer local-scale 3-D grid defined by the user. Secondly, it assesses the distribution of mass along the eruptive column, commonly by means of the radial averaged buoyant plume equations depending on the prognostic wind field and on the conditions at the vent (granulometry, mass eruption rate, etc). All these data serve as input for the fallout models. The initial version of the procedure includes only two Eulerian models, HAZMAP and FALL3D, the latter available as serial and parallel implementations. However, the procedure is designed to incorporate easily other models in a near future with minor modifications on the model source code. The last step is to postprocess the outcomes of models to obtain maps written in standard file formats. These maps contain plots of relevant quantities such as predicted ground load, expected deposit thickness and, for the case of or 3-D models, concentration on air or flight safety concentration thresholds.     

Effects of fish farm waste on Posidonia oceanica meadows: synthesis and provision of monitoring and management tools

This paper provides a synthesis of the EU project MedVeg addressing the fate of nutrients released from fish farming in the Mediterranean with particular focus on the endemic seagrass Posidonia oceanica habitat. The objectives were to identify the main drivers of seagrass decline linked to fish farming and to provide sensitive indicators of environmental change, which can be used for monitoring purposes. The sedimentation of waste particles in the farm vicinities emerges as the main driver of benthic deterioration, such as accumulation of organic matter, sediment anoxia as well as seagrass decline. The effects of fish farming on P. oceanica meadows are diverse and complex and detected through various metrics and indicators. A safety distance of 400 m is suggested for management of P. oceanica near fish farms followed by establishment of permanent seagrass plots revisited annually for monitoring the health of the meadows.     

An Upper Limit to Ground Deformation in the Island of Tenerife, Canary Islands, for the Period 1997–2006

Continuous monitoring of ground deformation in the volcanic island of Tenerife, Canary Islands, is based on GPS networks, since there are as yet no tiltmeter stations installed on the island. However, there is a world-class astronomical observatory on the island, the El Teide Observatory, where four tiltmeters, two aligned in the North-South and the other two in the East-West, are monitoring the movements of the solar telescope THEMIS. THEMIS (Heliographic Telescope for the Study of Solar Magnetism and Instabilites) is among the three largest solar telescopes in the world. Since THEMIS is located a few kilometers from the main volcanic structures of the island, in particular the El Teide-Pico Viejo stratovolcano, and the precision of the inclinometers is comparable to those used in geophysical studies, we carried out the analysis of the tilt measurements for the period 1997–2006. The tiltmeters at THEMIS are placed in the seventh floor of a tower, hence their sensitivity to geological processes is reduced compared to geophysical installations. However, THEMIS measurements are the only terrestrial data available in Tenerife for such a long period of observations, which include the sustained increase in seismic activity that started in 2001. In this sense, a significant change was found in the East-West tilt of approximately 35 μ-radians between the years 2000 and 2002. Some theoretical models were calculated and it was concluded that such tilt variation could not be due to dike intrusions, nor a volcanic reactivation below the El Teide-Pico Viejo volcano. The most likely explanation comes from dislocations produced by a secondary fault associated to a major submarine fault off the eastern coast of Tenerife. In any case, taking into account the nearly permanent data recording at THEMIS, they could be considered as a complement for any ground deformation monitoring system in the island.     

The use of taxonomic distinctness indices in assessing patterns of biodiversity in modular organisms

Estimating diversity of modular organisms may be problematic due to actual difficulties in discriminating between 'individuals' and quantifying their abundances. Quantitative data, when available, are collected through methods that could preclude the application of classical diversity indices, making comparisons among studies difficult. Taxonomic distinctness indices, such as the 'Average Taxonomic Distinctness' (Δ⁺) and the 'Variation in Taxonomic Distinctness' (Λ⁺) may represent suitable tools in investigating diversity beyond the simple species number. The potential usefulness of such indices has been explored almost exclusively on unitary organisms, neglecting modular ones. In this study, we employed Δ⁺ and Λ⁺ to analyse patterns of diversity of epiphytic hydroid assemblages living on Cystoseira seaweeds at a hierarchy of spatial scales, along 800 km of rocky coast (SE Italy). ANOVA on species richness and Λ⁺ showed no significant difference in sample diversity at the investigated spatial scales. In contrast, there were significant differences at the scale of 10s of km in Δ⁺. Analyses based on simulations detected significant variations at all spatial scales in Δ⁺. Such findings underline the potential of Δ⁺ in highlighting relevant spatial scales of variation in patterns of hydroid diversity. Our results also suggest that the interplay between natural environmental variations and the complex ecological traits of modular organisms might affect taxonomic distinctness indices. We stress the need for further investigations focusing on modular organisms before any generalizations on the use of taxonomic relatedness measures in examining marine biodiversity can be made.     

Differential feeding rates of native and alien predators on the invasive Asian date mussel Arcuatula senhousia (Benson in cantor, 1842) in a Mediterranean coastal lagoon

The alien Asian date mussel Arcuatula senhousia inhabits several coastal environments worldwide. This species can form dense mats where individuals attach through byssus threads, thus altering the structure, functioning and biodiversity of the native communities. We investigated the feeding preference of different predators on this alien species in a Mediterranean coastal lagoon. To do this, a mesocosm experiment was conducted using two crab species (the Mediterranean green crab Carcinus aestuarii) and the Say mud crab Dyspanopeus sayi, and one gastropod, the banded dye-murex Hexaplex trunculus as predators of A. senhousia with or without byssus mats. Our data suggest that C. aestuarii is a more effective predator against A. senhousia than D. sayi, and that H. trunculus is almost ineffective. A possible implication of this result is the potential use of the native crab C. aestuarii for limit the formation of the byssus mats, thus mitigating their potential negative effects on the native communities.     

Including root reinforcement variability in a probabilistic 3D stability model

Forests play a significant role in protecting people, settlements in mountainous terrains from hydrogeomorphic hazards, including shallow landslides. Although several studies have investigated the interactions between forests and slope instabilities, a full understanding of them has not yet been obtained. Additionally, models that incorporate forest stand properties into slope failure probability analyses have not been developed. In principle, physical‐based models, which are powerful tools for landslide hazard analyses, represent an appropriate approach to linking stand properties and slope stability. However, the reliability of these models depends on numerous parameters that describe highly complex geotechnical and hydrological processes (e.g. potential failure depth, saturation ratio, root reinforcement, etc.) that are difficult to measure and model. In particular, the spatial heterogeneity of root reinforcement remains a problem, and the use of physically based models from a forest management perspective has been limited. This paper presents a procedure for assessing slope stability in terms of the Factor of Safety that accounts for forest stand characteristics such as tree density, average diameter at breast height and minimum distance between trees. The procedure combines a three‐dimensional (3D) slope stability model with an evaluation of the variability of root reinforcement in terms of a probability distribution, according to forest characteristics. Monte Carlo simulation is used to account for the residual uncertainties in both stand characteristics and 3D stability model parameters. The proposed method was applied in a subalpine catchment in the Italian Alps, mainly covered by coniferous forest and characterized by steep slopes and high landslide risk. The results suggest that the procedure is highly reliable, according to landslide inventory maps [area under the ROC curve (AUC) is 0.82 and modified success rate (MSR) is 0.70]. Thus, it represents a promising tool for studying the role of root reinforcement in landslide hazard mapping and guiding forest management from a slope stability perspective. Copyright © 2017 John Wiley & Sons, Ltd.     

Plateau reduction by drainage divide migration in the Eastern Cordillera of Colombia defined by morphometry and 10Be terrestrial cosmogenic nuclides

Catchment‐wide erosion rates were defined using ¹⁰Be terrestrial cosmogenic nuclides for the Eastern Cordillera of the Colombian Andes to help determine the nature of drainage development and landscape evolution. The Eastern Cordillera, characterized by a smooth axial plateau bordered by steep flanks, has a mean erosion rate of 11 ± 1 mm/ka across the plateau and 70 ± 10 mm/ka on its flanks, with local high rates >400 mm/ka. The erosional contrast between the plateau and its flanks was produced by the increase in the orogen regional slope, derived from the progressive shortening and thickening of the Eastern Cordillera. The erosion rates together with digital topographic analysis show that the drainage network is dynamic and confirms the view that drainage divides in the Eastern Cordillera are migrating towards the interior of the mountain belt resulting in progressive drainage reorganization from longitudinal to transverse‐dominated rivers and areal reduction of the Sabana de Bogotá plateau. Copyright © 2016 John Wiley & Sons, Ltd.     

Factors determining subsidence in urbanized floodplains: evidence from MT‐InSAR in Seville (southern Spain)

Major rivers have traditionally been linked with important human settlements throughout history. The growth of cities over recent river deposits makes necessary the use of multidisciplinary approaches to characterize the evolution of drainage networks in urbanized areas. Since under‐consolidated fluvial sediments are especially sensitive to compaction, their spatial distribution, thickness, and mechanical behavior must be studied. Here, we report on subsidence in the city of Seville (Southern Spain) between 2003 and 2010, through the analysis of the results obtained with the Multi‐Temporal InSAR (MT‐InSAR) technique. In addition, the temporal evolution of the subsidence is correlated with the rainfall, the river water column and the piezometric level. Finally, we characterize the geotechnical parameters of the fluvial sediments and calculate the theoretical settlement in the most representative sectors. Deformation maps clearly indicate that the spatial extent of subsidence is controlled by the distribution of under‐consolidated fine‐grained fluvial sediments at heights comprised in the range of river level variation. This is clearly evident at the western margin of the river and the surroundings of its tributaries, and differs from rainfall results as consequence of the anthropic regulation of the river. On the other hand, this influence is not detected at the eastern margin due to the shallow presence of coarse‐grain consolidated sediments of different terrace levels. The derived results prove valuable for implementing urban planning strategies, and the InSAR technique can therefore be considered as a complementary tool to help unravel the subsidence tendency of cities located over under‐consolidated fluvial deposits. Copyright © 2017 John Wiley & Sons, Ltd.     

Geomorphological changes in an arid transgressive coastal dune field due to natural processes and human impacts

Geomorphological changes in recent decades in an arid transgressive coastal dune system (Maspalomas, Gran Canaria, Canary Islands) are analyzed. The methodology used is based on the generation of two geomorphological maps (1961 and 2003) by interpretation of digital orthophotos. The overlay of both maps in a geographic information system (GIS) enabled the spatial and surface changes of the landforms to be determined, and the processes that generated these changes. Twelve cultural and geomorphological processes were identified from highest to lowest importance, namely: anthropization by urban occupation (114 ha changed), stabilization (92.5 ha), barchanization (37 ha), salinization/halophytication (15 ha), anthropization (12.4 ha), deflation (11.8 ha), dune loss/beach gain (11.3 ha), dune formation (9.6 ha), progradation (8 ha), retrogradation (7.7 ha), destabilization (2.7 ha) and flooding (0.7 ha). Geomorphological changes are associated with a combination of five main factors, three of anthropogenic origin and two natural ones. The natural factors are: (1) the arid climate, which favors changes occurring at high speed; (2) the existence of a progressive sedimentary deficit. Anthropogenic factors are: (3) construction of tourist urbanizations, infrastructures and facilities; (4) installation of equipment or infrastructure on the beaches; (5) the activities carried out by users. These human factors have altered the aeolian dynamics and reduced the area occupied by vegetation in some areas, causing changes in aeolian sedimentary processes. The geomorphological processes identified can be used as indicators of environmental change, allowing us to synthesize the changes in landforms detected, and group all combinations derived from the analysis by GIS and analyze them spatially. Thus, the environmental changes in the transgressive coastal dune systems could be interpreted more effectively. Copyright © 2018 John Wiley & Sons, Ltd.