DInSAR analysis of ALOS PALSAR images for the assessment of very slow landslides: the Tena Valley case study

In this work we analyse the performance of advanced land observing satellite (ALOS) phased array type L-band syntetic aperture radar (PALSAR) images for mapping and monitoring of very slow landslides using conventional differential interferometry in the Tena Valley (Central Pyrenees, Spain). These results are compared with those retrieved in previous works where multi-band advanced differential interferometric synthetic aperture radar (DInSAR) analysis was performed for the same area using PSI techniques. The study area is largely underlain by slates (ca. 80 %) where large deep-seated very slow earth flows are dominant. The results reveal that DInSAR analysis is able to measure displacements of landslides with a greater spatial coverage than PSI analysis, but for a lower amount of them (nine against 51). Overall, the combination of the DInSAR and multi-band PSI analysis permitted to map and monitor 68 % of the landslides in Tena Valley. From this amount, 63 landslides are considered as active. The main advantage of DInSAR with respect to PSI analysis is the capability to detect faster movements (up to 145 cm?year^?1) derived from the 46 days interferograms. That is the case of Sextas and La Selva landslides where an acceleration of the moving mass was measured after intense rainfall periods producing major damages to linear infrastructures. The combination of measured displacement from ALOS interferograms, with the observed damages on the A-136 road, was useful to assess the potential damage that could cause these slow movements. In general, it is demonstrated that even though PSI analysis provides a better performance in terms of landslide mapping, L-band DInSAR analysis provides an added value for landslide hazard assessment through radar remote sensing. For this reason it is necessary to encourage the launch of new satellite missions similar to ALOS PALSAR that could operate with shorter revisiting time periods.     

Air masses and aerosols chemical components in the free troposphere at the subtropical northeast atlantic region

The dynamics and the aerosol chemistry of the air masses reaching the free troposphere of the subtropical Northeast Atlantic region during the period 1995–98 have been studied. Seven days backward trajectories were calculated daily with HYSPLIT-4 model for Izaña Global Atmospheric Watch (GAW) Observatory (28.3^°N 16.5^°W, 2367 m a.s.l.). These back-trajectories were classified by means of a k-means clustering strategy. The daily air masses have been coded using 16 variables to detect the aerosol load of each one of them. Four clusters were found: Cluster 1, representative of Atlantic oceanic middle troposphere air masses, (OMT), has an average frequency of occurrence of 50.6%. Cluster 2, which includes air masses originated in the African continent (AfD), has been recorded in a 19.8% of time. Cluster 3 represents a mixture at least of two of the next sources: Europe, Africa and Ocean, (EAM), with a frequency of 12.7%. Finally, Cluster 4 includes air masses with a high load of maritime aerosols, (MaA), and it has been detected in a 16.9%. An analysis of four aerosol components: NO₃ ^?, NH₄ ⁺, non-sea-salt-SO₄ ^2?, and mineral dust and its relation with the origin and transport of the air masses have been done. The highest quantities of mineral dust and nss-SO₄ ^2? are linked with African air masses with a mean value of 86.5 and 1.9 μg/m³ respectively. Whereas the highest levels of NO₃ ^?, 1.0 μg/m³, and NH₄ ⁺, 0.4 μg/m³, were obtained for AfD and EAM. The lowest levels were associated with OMT and MaA air masses types: 12.7, 0.6, 0.2, and 0.5 μg/m³ for dust, NO₃ ^?, NH₄ ⁺, and nss-SO₄ ^2? in average for the four studied years. However, it is remarkable that the values of the median for dust are 2.2 and 3.5 μg/m³ in clusters MaA and OMT respectively. Using non-parametric statistical tests the distributions of concentrations in each cluster by year have been compared in order to detect similarities. The results show that the aerosol loads of OMT and MaA air masses are quite similar and the same occurs for AfD and EAM air masses. However, the correlation analysis between the levels of anions and ammonium evidenced important differences among the air mass types. In AfD air masses is clear a low correlation between levels of nss-SO₄ ^2? and NH₄ ⁺ (r ² = 0.08) suggesting that the sulfate speciation was dominated by sulfate species others than ammonium sulfate, such as calcium sulfate. CaSO₄ ?2H₂O (gypsum) is mainly present in the coarse mode, where the radiative effects of sulfate are less important that in the accumulative mode. For OMT air masses is noticeable an important increasing on the correlation between the levels of anions and those of NH₄ ⁺ for the two last years of the study period (1997–1998, r ² = 0.61 –0.85%) with respect to the first ones (1995–1996, r ² = 0.25–0.49%), coinciding with the second strongest ENSO (El Niño Southern Oscillation) event recorded. This behavior indicates a change in the speciation of the aerosol component.     

Sediment resuspension in two adjacent shallow coastal lakes: controlling factors and consequences on phosphate dynamics

A combination of field measurements, modelling and laboratory experiments was used to evaluate the potential impact of sediment resuspension on phosphorus (P) dynamics. The study was carried out in two adjacent shallow coastal lakes (Lake Honda and Lake Nueva) which, due to their geographic proximity (only 200 m apart), are subject to equal meteorological forcing and represent ideal systems to study how morphometry and sediment properties relate to wind events. The focusing factors (a measure of the fluxes of sediment into the water column through resuspension) estimated by comparing settling fluxes measured in surface sediment traps with those measured in bottom traps, were significantly larger (approximately 34% larger) in Lake Honda (LH; 1.18) than in Lake Nueva (LN; 0.88). Our model estimates of resuspension fluxes (E) were also ca. 40% larger in LH than in LN, in agreement with the observed focusing factors. The larger resuspension fluxes encountered in LH, in comparison with LN, can mainly be explained by differences in lake morphometry. Still, they could arise from differences in grain size distribution or in benthic algae concentration encountered in the lake sediments. By means of adsorption experiments in the laboratory, we show that resuspension events will have different effects on P-dynamics in LH and LN. While the resuspended material from LH tends to adsorb phosphate (PO₄ ³⁻), removing it from the water column, in LN the resuspended sediments tend to increase the availability of PO₄ ³⁻ in solution. These differences arise from (1) higher concentrations of PO₄ ³⁻ in water in LH compared to LN; and (2) larger PO₄ ³⁻adsorption capacity of the LH sediments as a result of the more abundant iron oxyhydroxides and clay.     

A new steel framing system for seismic protection of timber platform frame buildings. Implementation with hysteretic energy dissipators

This paper describes a new seismic protection system for timber platform frame buildings, either for new construction or retrofit. The system consists in connecting the timber frame to a steel structure that includes hysteretic energy dissipators designed to absorb most of the seismic input energy thus protecting the timber frame and the other steel members; alternatively, the system might use other types of dissipative devices. The steel structure consists of four steel stacks (located at each of the four façades) and steel collectors embracing each slab; the stacks and the collectors are connected, at each floor level, through the energy dissipators. The steel structure is self‐supporting, that is, the timber frame is not affected by horizontal actions and can be designed without accounting for any seismic provision; in turn, the steel members do not participate in the main load‐carrying system. The timber‐steel interface is designed to avoid any stress concentration in the transfer of horizontal forces and to guarantee that the yielding of the dissipators occurs prior to any timber failure. The energy dissipation capacity of the suggested system is discussed, and an application example on a six‐story timber building is presented; this case corresponds to highly demanding conditions because of the relatively large building height and weight, the high local seismicity, and the soft soil condition. This research belongs to a wider project aiming to promote the structural use of timber by improving the seismic capacity of wooden buildings; this research includes experiments and advanced numerical simulation. Copyright © 2014 John Wiley & Sons, Ltd.     

Application of conditional geostatistical simulation to calculate the probability of occurrence of earthquakes belonging to a seismic series

Geostatistics offers various techniques of estimation and simulation that have been satisfactorily applied in solving geological problems. In this sense, conditional geostatistical simulation is applied to calculate the probability of occurrence of an earthquake with a lower than or equal magnitude to one determined during a seismic series. It is possible to calculate the energy of the next most probable earthquake from a specific time, given knowledge of the structure existing among earthquakes occurring prior to a specific moment.     

Simulating a seismic series using geostatistical and stochastic methods: application to the seismic series in the Alborán Sea (1997 June 24–?)

Seismic series can be taken as examples of correlated unstationary sets of time-stochastic sequences. We investigate the possibility of estimating what is most probable to occur subsequently, if we know the events that have occurred up to a given moment.
The stochastic methods can be used with data of the seismic series, irrespective of their genesis and origin. Using three stochastic methods, namely (1) simulating the likelihood of occurrence by conditional geostatistical simulation; (2) developing a stochastic analysis of the energy release by means of energy packages; and (3) calculating the occurrence time of the most probable next earthquake, we were able to simulate the occurrence of earthquakes that took place during the Alborán Sea seismic series (1997–1998).
We conclude that it is possible to set limits on the time of occurrence and energy release, understood as the magnitude of the most probable earthquake, during the development of a seismic sequence and prior to the actual occurrence of the earthquake.     

One million years of cultural evolution in a stable environment at Atapuerca (Burgos,Spain)

The present paper analyses the evidence provided by three sites (Sima del Elefante, Gran Dolina, and Galería) located in the Trinchera del Ferrocarril of the Sierra de Atapuerca. These three sites are cave infillings that contain sediments deposited from approximately 1.2 Ma to 200 kyr. Pollen, herpetofauna, and small and large mammal remains are used as proxies to obtain a general picture of the environmental changes that occurred at the Sierra de Atapuerca throughout the one million-year period represented at these sites. Similarly, cultural changes are tracked analyzing the evidence of human behavior obtained from the study of several bone and lithic assemblages from these three sites. At least three periods with different cultural features, involving technology, subsistence and behavior, are determined from the available evidence. The first two periods correspond to the Mode 1 technology and Homo antecessor: the first is dated around 1.2 to 1.0 Ma and reflects opportunistic behavior both in technology and subsistence. The second period is around 800 kyr BP. Mode 1 technology is still maintained, but subsistence strategies include systematic hunting and the use of base camps. The third period is dated between 500 ka and 200 ka and corresponds to the Mode 2 technology and the acquisition of directional hunting and other organizational strategies by Homo heidelbergensis. A transition from Mode 2 to Mode 3 seems to appear at the end of this time-range, and may reflect the early phases of a fourth cultural change. With regard to the environment, our main conclusion is that there was an absence of extremely harsh conditions at Atapuerca throughout this time period. The presence of Mediterranean taxa was constant and the dominant landscape was a savannah-like open environment, probably with small forest patches. An alternation of Mediterranean and mesic species as the dominant component of the tree storey was induced by the climatic cycles, and steppes spread across the landscape during the drier periods. In any case, it is not possible to establish clear cut-off points separating entirely different environmental episodes. Our results show no evidence of any relationship between environmental change and cultural change at the Sierra de Atapuerca.     

Freeze–thaw cycles and rainfall as triggering factors of mass movements in a warm Mediterranean region: the case of the Tramuntana Range (Majorca, Spain)

Between 2008 and 2010, the island of Majorca (Spain) experienced the coldest and wettest winters of the last 40 years. Accumulated rainfall was twice the average and values of intense rainfall up to 296 mm/24?h were recorded, very similar to those calculated for a return period of 100 years. Additionally, high precipitation coincided with anomalous, low temperatures, with abundant snowfall and freezing in the highest zones of the Tramuntana Range, in the northwest sector of the island. As a result, 34 mass movements were recorded on the range, which seriously affected the road network in an area of great importance for tourism, as it welcomes 8.5 million visitors each year. Fourteen rockfalls, 1 rock avalanche, 15 landslides and 4 karstic collapses were inventoried. The geological structure, formed by a series of NW overlapping thrusts, determines the distribution as well as the failure pattern of the movements. Thus, the northern face of the range registered 68% of the mass movements: nine rockfalls with planar failure took place as well as all the landslides recorded. Likewise, south-facing slopes have been affected by longer runout rockfalls with a wedge-type failure. The thorough analysis of the meteorological data shows that most of the movements have taken place after antecedent rainfall over 800?mm. Additionally, the rockfalls have also occurred after several freeze–thaw cycles, being a determining and unusual factor in this warm region. Intense rainfall >90 mm/24?h also caused rockfalls as well as exceptional very intense rainfall >120 mm/24?h caused landslides. The results aim to contribute to the design of an early warning system coordinating emergency, infrastructure services and meteorological centres in a region of high risk.     

Variation in transparent exopolymer particles in relation to biological and chemical factors in two contrasting lake districts

In inland waters, transparent exopolymer particles (TEP) can affect carbon export and sequestration in sediments with consequences for lake C budgets. We measured TEP concentration in 32 lakes from two contrasting lake districts covering wide ranges in biological and chemical characteristics. North temperate lakes, located in a wet region, have low to moderate ionic strength and low to high dissolved organic carbon with corresponding variation in color (light absorbance). Mediterranean lakes located in a semiarid region were characterized by high ionic strength and high concentrations of dissolved organic carbon but low color. TEP concentrations were large relative to the living portion of the particulate organic carbon pool in both Mediterranean (36%) and north temperate (33%) lakes. TEP concentrations ranged from 36 to 1,462 μg [as Gum Xanthan equivalents (GX eq)] L⁻¹ in north temperate lakes. In the Mediterranean lakes, concentrations were higher that previously reported for other systems and ranged from 66 to 9,038 μg GX eq L⁻¹. TEP concentration was positive and significantly related to chlorophyll a (chl a) in north temperate lakes and in the entire data set. Although a significant and positive relationship between TEP and chl a was also detected in the Mediterranean lakes, bacterial abundance was most strongly related to TEP. In contrast with the positive influence of phytoplankton and bacteria on TEP, there were weaker relationships between TEP and the chemical variables tested. We observed a significant and positive relationship between pH and TEP (for all lakes) but this relationship was indirectly driven by a co-variation of pH with phytoplankton biomass based on multiple regression analysis. For the Mediterranean lakes, the negative (but not significant) trends between TEP and both conductivity and divalent cations suggest thresholds above which TEP will likely be destabilized. Under these conditions, TEP may flocculate or disperse in the water column.     

Spectral analysis of climate cycles to predict rainfall induced landslides in the western Mediterranean (Majorca,Spain)

In the present work, spectral analysis has been applied to determine the presence and statistical significance of climate cycles in long-term data series from different rainfall and gauging stations located in the Tramuntana Range, in the north-western sector of the island of Majorca. Climate signals recorded previously in the Mediterranean region have been identified: the ENSO, NAO, HALE, QBO and Sun Spot cycles as well as others related to solar activity; the most powerful signals correspond to the annual cycle, followed by the 6-month and NAO cycles. The incorporation of data derived from gauging stations contributes to better climate signal detection as local and exceptional influences are eliminated. Simulations have been performed for each rainfall/gauging station, using the most significant climate cycles obtained by means of the power spectrum. A good correlation between rainfall/flow values and simulated cycles has been obtained. The NAO and ENSO cycles are the most influential in the rainy periods, and specifically the NAO cycle, where a good correlation between episodes of high rainfall/flow and high values of ANAOI can be observed. At a second stage, landslides dated and recorded in the Tramuntana Range since 1954 (174 events) have been correlated with the simulated cycles obtaining good results, as the landslide events match rainfall peaks well. The correlation for the past decade (since 2005), when a detailed landslide inventory is available, also reveals a coincidence between landslide events and climate cycles, and specifically NAO and ENSO cycles. That is the case of the period 2008–2010, when numerous mass movements took place, and when the largest movement of the inventory was recorded. Results show a potential rainy period in the Tramuntana Range for the coming years (with maximum values around year 2021), when conditions similar to those related to the 2008–2010 event could take place again. The methodology presented in this work can contribute to the prediction of temporal, extreme hydrological events in order to design short-/medium-term mitigation strategies on a regional scale.