Direct and Indirect pCO2 Measurements in a Wide Range of pCO2 and Salinity Values (The Scheldt Estuary)

Recent improvements in both Infra-red spectroscopy and equilibrator techniqueshave allowed to determine, for the first time, pCO₂using simultaneously and continuously both the direct and indirect methods in an estuary where pCO₂ values range from 500 to 8500 atm and salinity from 0 to 30. Our results show that both methods are in excellent agreement in the wholeestuary (r² = 0.999, n = 1075, p < 0.0001). Thus, the NBS (US National Bureau of Standards) scale, although inadequate for seawater samples, is appropriate for estuarine waters and can be applied with confidence to calculate pCO₂.     

Coseismic and post-seismic signatures of the Sumatra 2004 December and 2005 March earthquakes in GRACE satellite gravity

The GRACE satellite mission has been measuring the Earth's gravity field and its temporal variations since 2002 April. Although these variations are mainly due to mass transfer within the geofluid envelops, they also result from mass displacements associated with phenomena including glacial isostatic adjustment and earthquakes. However, these last contributions are difficult to isolate because of the presence of noise and of geofluid signals, and because of GRACE's coarse spatial resolution (>400 km half-wavelength). In this paper, we show that a wavelet analysis on the sphere helps to retrieve earthquake signatures from GRACE geoid products. Using a wavelet analysis of GRACE geoids products, we show that the geoid variations caused by the 2004 December ( M _w= 9.2) and 2005 March ( M _w= 8.7) Sumatra earthquakes can be detected. At GRACE resolution, the 2004 December earthquake produced a strong coseismic decrease of the gravity field in the Andaman Sea, followed by relaxation in the area affected by both the Andaman 2004 and the Nias 2005 earthquakes. We find two characteristic timescales for the relaxation, with a fast variation occurring in the vicinity of the Central Andaman ridge. We discuss our coseismic observations in terms of density changes of crustal and upper-mantle rocks, and of the vertical displacements in the Andaman Sea. We interpret the post-seismic signal in terms of the viscoelastic response of the Earth's mantle. The transient component of the relaxation may indicate the presence of hot, viscous material beneath the active Central Andaman Basin.     

Reconstructing spatio-temporal patterns of debris-flow activity using dendrogeomorphological methods

Debris flows are a major threat in many parts of the Alps, where they repeatedly cause severe damage to infrastructure and transportation corridors or even loss of life. Nonetheless, the spatial behavior of past debris-flow activity and the analysis of areas affected during particular events have been widely neglected in reconstructions so far. It was therefore the purpose of this study to reconstruct spatio-temporal patterns of past debris flows on a forested cone in the Swiss Alps (Bruchji torrent, Blatten, Valais). The analysis of past events was based on a detailed geomorphic map (1:1000) of all forms related to debris flows as well as on tree-ring series from 401 heavily affected trees (Larix decidua Mill. and Picea abies (L.) Karst.) growing in or next to deposits. The samples were analyzed and growth disturbances related to debris-flow activity assessed, such as tangential rows of traumatic resin ducts, the onset of reaction wood or abrupt growth suppression or release.In total, 960 growth disturbances were identified in the samples, belonging to 40 different event years between A.D. 1867 and 2005. In addition, the coupling of tree-ring data with the geomorphic map allowed reconstruction of eleven formerly active channels and spatial representation of individual events. Based on our results we believe that before 1935, debris flows preferentially used those channels located in the western part of the cone, whereas the eastern part of the cone remained widely unaffected. The spatial representation of the 40 events also allowed identification of five different spatial patterns for debris flows at the study site.     

Iodine concentrations of soils near Trabzon, Turkey: a region of endemic goiter

Iodine contents of soils developed over the major rock formations of the northern zone of the Eastern Pontide Tectonic Belt (Northeastern Turkey) have been investigated with respect to soil-parent rock relationship, effect of topography, elevation, and climate to construe its effect on the health of the local population. Samples were collected from the A and B horizons of the soils developed over the major stratigraphic units constituting the eastern Pontides, including the Lower Basic Complex of Jurassic-Lower Cretaceous age, the Berdiga limestone (Jurassic-lower Cretaceous), the Dagbasi granitoid (Upper Cretaceous), volcano-sedimentary sequence of Upper Cretaceous age, ore-bearing and barren dacites of Upper Cretaceous age, and Neogene alkaline basalts. Chemical analyses of soil samples indicate significantly lower iodine abundances for all the soils studied (5–28 ppm) in comparison to the average abundance of iodine in analogous soils of other parts of the world (22–93 ppm). The concentration of iodine in soils developed over the same geologic formation decrease with increasing elevation. In certain cases, this decrease may reach up to 70%. Goiter is highly common throughout this region in Turkey. The results of this study suggest that the iodine deficiency of region’s soils may be a principal underlying cause for this area of Turkey being an endemic goiter region.     

Response of littoral chironomid communities and organic matter to late glacial lake—level,vegetation and climate changes at Lago dell’Accesa (Tuscany,Italy)

This study focuses on the response of lacustrine littoral chironomid communities to late glacial changes in limnological, environmental and climate conditions in the Mediterranean context. Late glacial chironomid (Diptera: Chironomidae) assemblages, organic petrography and geochemistry were analysed in a sediment core from the littoral zone of Lago dell’Accesa (Tuscany, Italy), where the lake-level fluctuations and the vegetation history have been previously reconstructed. Comparison of the chironomid stratigraphy to other proxies (pollen assemblages, organic petrography and geochemistry, lake-level) and regional climate reconstruction suggested the predominant influence of lake-level changes on the littoral chironomid fauna. The main lowering events that occurred during the Oldest and the Younger Dryas were followed by higher proportions of taxa typical of littoral habitats. A complementary study of organic matter suggested the indirect impact of lake-level on the chironomids through changes in humic status and habitat characteristics, such as the type of substrate and aquatic macrophyte development. Several chironomid taxa, such as Glyptotendipes, Microtendipes and Cricotopus type patens, were identified as possible indicators of low lake-level in the late glacial records. Nevertheless, this study suggested that parallel analyses of organic matter and chironomid assemblages may be needed to circumvent misinterpretation of littoral chironomid assemblage stratigraphy. There was a weak response of the chironomid assemblages to small lake-level lowerings that corresponded to the Older Dryas and Preboreal oscillations. A higher level of determination, e.g. to the species group level, may be necessary to increase the sensibility of the indicators to lake-level changes.     

Spatial variability and non-linearity of strong ground motion near a fault

We present observations of ground accelerations recorded at a small array close to the fault during the Düzce earthquake and its early aftershocks. The records show the strong spatial variability of ground acceleration over distances of only a few hundred metres. During the main shock, the peak horizontal acceleration values ranged from 0.3 to about 1.0 g at stations distant of 1.5 km only. We attribute this spatial variability to a fault zone site effect as peak ground acceleration steadily increases as the distance to the fault trace decreases. The spectral ratio between the ground motion recorded near the fault and the one outside the fault zone shows a shift of the spectral peak to lower frequencies with increasing peak accelerations. Such an observation suggests a non-linear behaviour of the fault zone due to the strong ground shaking. As much as a 45 per cent reduction in the shear wave velocity is necessary for the observed shifts. The opening of pre-existing cracks throughout the fault zone is the proposed mechanism to account for the observed shear wave reductions. The observation that elastic fault zone properties are soon recovered following episodes of large strains shows that cracks and fissures close rapidly after the strong shaking is over.     

A simplified approach for vulnerability assessment in moderate-to-low seismic hazard regions: application to Grenoble (France)

Due to the moderate seismic risks in France, the building vulnerability assessment methods developed for high seismic risk countries could not easily be used here because of their cost and the low-risk perception among the public and officials. A light vulnerability assessment method is proposed and tested in Grenoble (France), based on classes and scores provided in the GNDT method but simplified in terms of visual screening and number of structural parameters used. Compared to the RiskUE method, the damage obtained by our approach shows that 90% of buildings have residuals smaller than 0.2, i.e. one grade of the EMS98 damage scale. A large scale survey is devised and conducted among the inhabitants of Grenoble in order to collect the main structural parameters. By comparing the results from the survey to the historical urbanization of Grenoble and to expert surveys performed in two urban districts, the information useful for the light method of vulnerability assessment can be rapidly collected by non-experts reducing substantially the estimate cost. The average damage is then computed using the GNDT formula considering the probable intensities which could be observed in Grenoble (VII and VIII). The average damage reaches 0.4 in the oldest part of Grenoble mainly made of masonry buildings and 0.2 in reinforced concrete suburbs where reinforced concrete predominates. The results are a relative vulnerability assessment that provides useful initial information for the urban zones of Grenoble where the vulnerability is higher. This method can be used to classify the seismic vulnerability in wide seismic-prone regions to a fair degree of accuracy and at low cost.     

松潘-平武地震前地震视应变场的时空演变

利用松潘-平武周边地区的地震资料研究了1970-1975年该地区地震视应变场的分布和时空变化特征。结果表明,地震视应变的时空变化与松潘-平武强震具有很好的对应关系,1970年在附近就出现异常区,并且地震视应变总体上逐年增加,地震就发生在地震视应变异常区。     

2006年甘肃文县5.0级地震灾害损失评估

2006年6月21日在甘肃省文县发生MS5.0地震,造成了建筑物破坏及人员伤亡。在震后开展的地震现场考察与震害评估工作中,将灾区分为2个评估子区,完成了29个点的震害抽样调查工作,根据地震灾害损失评估系统EDLES2.5的要求建立了有关数据库,做出了经济损失评估,并针对灾害特点给出了灾区恢复重建的建议。