Les terrasses marines, marqueurs de l'interaction entre soulèvement et oscillation du niveau de la mer

National audienceBilan des mesures de soulèvement grâce aux terrasses marine

Coastal Uplift along the Eastern Black Sea Coast: New Marine Terrace Data from Eastern Pontides, Trabzon (Turkey) and a Review

International audienceAn emerged, Quaternary, marine terrace sequence has been investigated near Trabzon, Turkey, along a 20-km-long stretch of the coast of the southeastern Black Sea. The sequence includes seven principal marine terraces. The terraces are frequently compound and include up to three second-order marine terraces. The upper shoreline angles of the main terraces were found at the following maximum elevations above mean sea level: 3 ± 0.5 m (TH), 12 ± 3 m (T1), 36 ± 2 m (T2), 79 ± 9 m (T3), 120 ± 3 m (T4), 138 ± 10 m (T5), and 260 ± 25 m (T6). Fossil bivalves and gastropods from the TH, T1, T2, and T3 deposits have been dated by Electron Spin Resonance (ESR). The results show that the ages of the deposits from the TH, T1, T2, and T3 terraces are 5.141 ± 0.294 ka, 124.8 ± 26.0 ka, 292.5 ± 49.8 ka, and 407.998 ± 67.475 ka, respectively. Consequently, we correlate TH, T1, T2, and T3 to marine isotope stage (MIS) 1, 5e, 9, and 11, which correspond to 5, 123, 321, and 400 ka highstands, respectively. Estimated uplift rates deduced from the elevations of T1, T2, and T3 are 0.07 ± 0.05, 0.10 ± 0.02, 0.17 ± 0.03 mm/y or m/ka. These results show nonsteady, long-term uplift rates. Extrapolation of the oldest uplift rate (i.e., determined on the highest dated terrace) shows that in the region of Trabzon, Turkey, coastal, positive, vertical deformations are recorded at 2 Ma, which corresponds to the extrapolated age of the highest terrace in the sequence. Comparison with other sequences on the Black Sea coast reveals a rather weak uplift in this zone, which can be considered significative for the recent uplift of the Eastern Pontides

Does Kamchatka belong to North America? An extruding Okhotsk block suggested by coastal neotectonics of the Ozernoi Peninsula, Kamchatka, Russia

International audienceThis paper addresses one part of an outstanding tectonic problem regarding the nature of the plate boundary between Eurasia and North America in northeastern Russia. In this region, the northwestern corner of the Pacific plate interacts either simply with the North American plate, or more complexly with one or more blocks independent of North America. North of this corner, evidence of uplift, tilting, and convergence contradicts the prevailing, simpler model. On the Ozernoi Peninsula, ;150 km north of the subducting Pacific plate, marine terraces indicate uplift rates of 0.1 to 0.3 mm/yr, with faster rates to the east. Historic and paleoseismic records provide evidence for recurring tsunamigenic, thrust earthquakes offshore of the Ozernoi Peninsula, the most recent a Mw 7.7 earthquake in 1969. A multiplate model where an eastward-moving Okhotsk block, including most of Kamchatka, is converging with a clockwise-rotating Bering block better explains these observations than does the unbroken North American plate model

Patologías de origen térmico en estructuras

Una de las causas más frecuentes de la aparición de patologías en edificios es la incorrecta consideración de los efectos de origen térmico, que se manifiestan normalmente en fisuras, pérdidas de estanqueidad, humedades etc. Para facilitar el análisis se pueden separar en dos tipos: Los debidos a gradiente térmico y los debidos a dilatación térmica

Present-day trends of vertical ground motion along the coast lines

International audienceVertical ground motion (VGM) rates stand as crucial information, either for predicting the impact of the actual sea level rise along low-lying coasts or refining geodynamic problems. Because present day VGM rates have a magnitude smaller than 10 mm/yr, they remain challenging to quantify and often elusive. We focus on the quantification of global-scale VGM rates in order to identify global or regional trends. We computed VGM rates by combining tide gauges records and local satellite altimetry, which yield a new dataset of 634 VGM rates. We further compare this database to previous studies that use geodetic techniques and tide gauges records in order to evaluate the consistency of both our results and previous ones. The magnitudes differ by less than 5 mm/yr, and similar subsidence and uplift general tendencies appear. Even if the asset of our database stands in the greater number of sites, the combination of all studies, each with different pros and cons, yields a hybrid dataset that makes our attempt to extract VGM trends more robust than any other, independent study. Fennoscandia, the West coast of North America, and the eastern coast of Australia are uplifting, while the eastern coast of North America, the British Isles and Western Europe, the eastern Mediterranean Sea, Japan, and the western coast of Australia are subsiding. Glacial Isostatic Adjustment (GIA) is expected to provide a major contribution to the present-day signal. Aside from Fennoscandia, observed VGM often depart from the GIA model predictions of Peltier (2004). This either results from an underestimate of the model predictions or from the influence of other processes: indeed, the influence of the geodynamic setting appears in particular along the coasts of western North America or Japan, where the alternation of transform faults and subduction zones makes it possible to assign contrasted behaviours to the local geodynamic context. Local mechanisms like anthropogenic processes or sediment compaction, also contribute to VGM. This remains true for the critical cases of Venice, the Gulf of Mexico, the Ganges delta, and the Maldives, which are particularly exposed to the current sea level rise

Deformación de losas sin vigas. Influencia de la resistencia a la flexotracción

Las losas sin vigas de hormigón armado han tenido una difusión muy importante en nuestro continente en los últimos 10 años, siendo utilizadas de modo sistemático en edificios de vivienda, hoteles, oficinas estacionamientos etc. Se sabe que el hormigón es un material muy noble en cuanto a su resistencia, pero es difícil de predecir en cuanto a sus deformaciones por flexión. En elementos tipo viga se ha logrado una cuantificación suficientemente aproximada del fenómeno mediante la fórmula de Branson o los diagramas momento-curvatura bi o trilineales. En las losas sin vigas desde un punto de vista cualitativo, se puede afirmar que intervienen los mismos parámetros, pero la fenomenología y la modelización matemática resulta mucho más complicada. No obstante mediante la teoría de la fisuración distribuida, la ortotropía del hormigón fisurado y la teoría de los elementos multicapa se puede lograr expresar las ecuaciones constitutivas del hormigón armado en estado no lineal. Esta modelización combinada con los elementos finitos apropiados llevan a una metodología de cálculo que mediante un proceso de aproximaciones sucesivas permite calcular con suficiente aproximación cualquier tipo de losa.&nbsp

Quaternary coastal uplift along the Talara Arc (Ecuador, Northern Peru) from new marine terrace data

Marine Geology, v. 228, n. 1-4, p. 73-91, 2006. http://dx.doi.org/10.1016/j.margeo.2006.01.004International audienceMarine terrace sequences have been investigated along the Talara Arc, a 1000-km-long stretch of the coast of Ecuador and northern Peru, characterized by subduction with a concave plan-view. Seven areas were investigated, evidencing flights of up to seven marine terraces with elevations reaching up to 360 m above mean sea level (amsl). Dating of the terraces was made using the Infra Red Stimulated Luminescence (IRSL) technique on sands as old as MIS 9 (∼330 ka). 14 C and U-series dates were obtained from fossil shells for geochronological cross control. Mean uplift rates along the Talara Arc range from about 0.10 up to 0.50 mm/ yr. The strongest uplift is observed in the Manta Peninsula of Ecuador in front of the subduction of the Carnegie Ridge. The uplift rate tends to slow down towards the northern and southern ends of the Talara Arc and then the transition toward the stable or subsiding coasts of central Peru and northern Ecuador and Colombia is sharp. The uplift appears to be homogeneous and related to 1) the map view curvature of the Arc, 2) the concave subduction pattern and 3) the Carnegie Ridge subduction

Influencia del curado en la resistencia a compresión del hormigón: estudio experimental

This paper presents an experimental verification to analyzes the influence of curing on concrete compressive strength. The study consist in testing several specimens from the same concrete mix, exposed to different humidity conditions (100% and 50% humidity) Comparisons were also made for different mixes. For example, the major differences in compressive strength subjected to different curing conditions were obtained for the lower water/cement ratios.Este artículo presenta una comprobación experimental sobre la influencia del curado en la resistencia a compresión del hormigón. El estudio consiste en ensayar a compresión probetas provenientes de una misma mezcla de hormigón, pero sometidas a condiciones de humedad decurado distintas (100% y 50% de humedad). Las comprobaciones también fueron realizadas para diferentes dosificaciones. Por ejemplo, las mayores diferencias, en la resistencia a compresión del hormigón sometido a diferentes condiciones de curado, fueron obtenidas para las menoresrelaciones agua/cemento

Uplift of Quaternary shorelines in Eastern Patagonia : Darwin revisited

International audienceDuring his journey on the Beagle, Darwin observed the uniformity in the elevation of coastal Eastern Patagonia along more than 2000 km. More than one century later, the sequences of Quaternary shorelines of eastern Patagonia have been described and their deposits dated but not yet interpreted in terms of geodynamics. Consequently, we i) mapped the repartition of the Quaternary coastal sequences in Argentinean Patagonia, ii) secured accurate altitudes of shoreline angles associated with erosional morphologies (i.e. marine terraces and notches), iii) took into account previous chrono-stratigraphical interpretations in order to calculate mean uplift rates since ~440 ka (MIS 11) and proposed age ranges for the higher and older features (up to ~180 m), and iv) focused on the Last Interglacial Maximum terrace (MIS 5e) as the best constrained marine terrace (in terms of age and altitude) in order to use it as a tectonic benchmark to quantify uplift rates along the entire passive margin of Eastern South America. Our results show that the eastern Patagonia uplift is constant through time and twice the uplift of the rest of the South American margin. We suggest that the enhanced uplift along the eastern Patagonian coast that interested Darwin during his journey around South America on the Beagle could originate from the subduction of the Chile ridge and the associated dynamic uplift

Holocene coquina beachrock from Haishan Island, east coast of Guangdong Province, China

International audienceCoquina beachrock, with a thickness of 10 m and an exposed surface area covering 3.4 km2, is well developed along the southern coast of Haishan Island on the east coast of Guangdong Province, South China. Part of the deposit not treated in this study also extends under the surface of the sea. The coquina beachrock was deposited in a large embayment semi-enclosed by palaeocoastal hills and islands, but with good marine circulation. Holocene strata on Haishan Island demonstrate a mixed carbonate/siliciclastic regime in a series of fining- and deepening-upward shelly limestone successions. Mass accumulations of whole and fragmented mollusc shells are the most remarkable features expressed throughout the series. Coralline red algae are commonly found overgrowing the bivalve bioclasts. Other bioclasts include gastropods, coralline red algae, bryozoans, foraminifera, and scleractinian coral. Cement is well developed within the interstices formed by the bioclasts, showing two or three generations of development. On both a qualitative and quantitative basis, the consecutive coquina series document an overall shallowing-upward pattern of beachrock deposition, which was strongly influenced by marine transgression on Haishan Island. Dating by AMS 14C indicates an age in the Middle to early Late Holocene for these coquina beachrock deposits. Siliciclasts incorporated within the beachrock deposits mainly consist of quartz grains. Not fully hardened, the binding cement is high in calcium carbonate, including aragonite mud, fibrous aragonite and granular calcite. Such carbonate deposits dominated by mollusc bioclasts with quartz grains indicate a pattern of littoral sedimentation. The massive coquina beachrock on the southern coast of Haishan Island formed during Middle to early Late Holocene time, and represents a highstand of sea level from 4000 BP to 2800 BP with short-lived and rapid sea level fall