Search publications of the members of the Royal Belgian institute of natural Sciences
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Bedrock morphology modelling using geologically-dependent empirical equations between resonance frequency and bedrock depth
- Calculating thickness variations of soft sediments above bedrock is important for site effect characterisation, earthquake ground motion amplification and for hydrogeological and geothermal purposes. In case seismic array instrumentation is not available and hence shear-wave velocity profiles cannot be obtained, other correlation techniques need to be applied to accurately deduce bedrock depth. Nakamura’s H/V Spectral Ratio (HVSR) analysis of ambient noise is a powerful seismological method to reveal a site’s resonance frequency. The conversion from a resonance map to a bedrock depth map in areas with a different sedimentary cover in terms of layer thickness and lithologies is, however, not straightforward. Converting resonance frequencies to depth by applying a mean shear-wave velocity (Vs) will under- and overestimate bedrock depth at higher and lower topographies, respectively. Applying an empirical log-log (powerlaw) relationship between resonance frequency (obtained from HVSR analyses) and bedrock depth (obtained from boreholes) provides a much better depth estimation that considers the non-linear increase of Vs with depth. Accurate empirical equations can however only be constructed from HVSR measurements performed in areas with similar lithological sediments. In this study we present a high-resolution microzonation study performed in Brussels (Belgium) where both the sedimentary cover and the fractured top of the bedrock (i.e. the Brabant Massif) are of interest for their geothermal potential. Using 88 ambient noise measurements above boreholes we constructed four different powerlaw equations that are applicable to convert resonance frequency to depth in areas with a clayey, sandy-clayey, alluvial-clayey and alluvial sedimentary cover. Subsequently, 405 ambient noise measurements were conducted and converted to virtual boreholes using these four empirical equations. Measurements were used to map out bedrock depth in a 15km2 and a 25 km2 area applying a 200 m and 500 m station density spacing, respectively. The results demonstrate the presence of NW-SE oriented, 20 m-high ridges at 100 m depth that stand out because of differential erosion between less-resistant slaty (Tubize Formation) and hard quartzitic (Blanmont Formation) rock formations of the Brabant Massif. Separating seismic data according to their subsurface geology results in more accurate empirical frequency-depth conversion equations than if only one equation would be used for an entire area.
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Integration of corrective parameters to merge multiple-sourced online macroseismic data
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Investigations géophysiques du plancher calcite et du remplissage sédimentaire de la Salle de la structure de Bruniquel
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Crowdsourcing in Europe: how to share macroseismic data of felt earthquakes ?
- https://blogs.egu.eu/divisions/sm/2017/11/20/crowdsourcing-in-europe-how-to-share-macroseismic-data-of-felt-earthquakes/
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Incorporating data uncertainty in 3D voxel modelling and the importance in decision making
- Geological databases resulting from the merging of various data sources and time periods jeopardize harmonization of data products. Data standardization is already common practice and a first step in avoiding semantic overlap. European marine data management infrastructures provide such standards, e.g., Geo-Seas (http://www.geo-seas.eu/) for geological data and SeaDataNet (https://www.seadatanet.org/) for marine metadata in general. In addition, metadata quality control is important, though data uncertainty is seldom quantified and to be used in modelling. Preliminary uncertainty analyses were worked out to provide an extra dimension to the cross-border 3D voxel models of the geological subsurface of the Belgian and southern Netherlands part of the North Sea (http://odnature.naturalsciences.be/tiles/). Starting from simple quality flagging in geological databases and model uncertainty calculations (probability and entropy) in the 3D modelling, data uncertainty (e.g., related to qualities in positioning, sampling and vintage) is now quantified. Combining all uncertainties remains a challenge, as well as communicating their importance in decision making. A demonstration will be given on the status of the uncertainty analyses and how these are incorporated in a newly developed decision support tool allowing interactive querying of the 3D voxel model, now comprising geological, as well as entropy, probability and data uncertainty attributes (figure 1).
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Givetian rugose corals from the Zemmour in Mauritania
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Update of the Devonian lithostratigraphic subdivision in the subsurface of the Campine Basin (northern Belgium)
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Ecology of Devonian ostracods: application to the Frasnian/Famennian boundary bioevent in the type region (Dinant Synclinorium, Belgium)
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Ostracod and rock facies across the Emsian/Eifelian boundary at Couvin (Dinant Synclinorium, Belgium)
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New data on the osteoglossid fishes (Teleostei, Osteoglossiformes) from the Marine Danian (Paleocene) of Landana (Cabinda Enclave, Angola)
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Comments on the phylogenetic relationships of Pholidorhynchodon malzannii and of Eurycormus speciosus (Teleostei, Pholidophoriformes), two Mesozoic tropical fishes.
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Osteology and relationships of Luxembourgichthys (« Pholidophorus ») friedeni gen. nov. (Teleostei, Pholidophoriformes) from the Lower Jurassic of Belgium and the Great Duchy of Luxemburg.
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On the presence of the plethodid fish Dixonanogmius (Teleostei, Tselfatiiformes) in the marine Upper Cretaceous of Burma (Myanmar), tropical Asia.
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Osteology and relationships of Signeuxella preumonti (Teleostei, Pholidophoriformes, Signeuxellidae) from the continental Middle Jurassic (Stanleyville Formation) of Kisangani (Democratic Republic of Congo)
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Systematic revision of the Cretaceous actinopterygian fauna from Bernissart, Belgium.
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Osteology and relationships of Italophiopsis derasmoi gen. and sp. nov. (Halecomorphi, Ionoscopiformes) >From the marine Early Cretaceous of Pietraroja (Campania, southern Italy).
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Revision of « Chanos » leopoldi (Teleostei, Gonorynchiformes, Chanidae) from the marine Albian (Early Cretaceous) of Pietraroja Campania, southern Italy) and the resurrection of the genus Caeus Costa, 1857.
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A handful of duck radiuses: Peculiarities of the avifaunal exploitation at the Gravettian site of Maisières‐Canal (Belgium)
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An enigmatic new ungulate-like mammal from the early Eocene of India
- We report a new genus and species of herbivorous mammal, Pahelia mysteriosa, from the early Eocene Cambay Shale Formation, Tadkeshwar Lignite Mine, Gujarat, India. The new taxon, approximately the size of a small phenacodontid (e.g. Ectocion parvus), is represented by three mandibular fragments, the most complete of which documents nearly the entire symphysis and mandibular body plus P3–M3. Pahelia has incipiently selenolophodont molars with strong exodaenodonty, absent paraconids, weak but distinct entolophids, and prominent ectostylids. Molar size increases distally, but M3 does not develop a prominent third lobe. Premolars are simple, with prominent protoconids and short talonids but little development of other trigonid cusps. The mandibular symphysis is strongly fused, and there is an enlarged alveolus for an anterior tooth. The combination of features present in the new taxon does not closely match that of any known mammal, but there are some similarities to a diversity of ungulates from Africa, Asia, Europe and North America. Preserved morphology is insufficient to assess the affinities of the new taxon with confidence, but a link to Quettacyonidae, also endemic to the Indian subcontinent, is morphologically and biogeographically plausible. If this scenario is correct, it suggests that P. mysteriosa could be a part of the endemic mammalian fauna of India prior to its initial faunal contact with Asia.
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A well-preserved pelvis from the Maastrichtian of Romania suggests that the enigmatic Gargantuavis is neither an ornithurine bird nor an insular endemic
- We describe a well-preserved pelvis from the Maastrichtian S^anpetru Formation of the Hat¸ eg Basin in Romania. The fossil closely resembles the pelvis of Gargantuavis philoinos from the Ibero-Armorican Peninsula, but differs in a smaller size and a few morphological features. It constitutes the first record of Gargantuavis outside the Ibero-Armorican Island and is more complete than any of the previously known Gargantuavis pelves. The new fossil allows the recognition of characteristics previously unknown for Gargantuavis. These include the presence of large supratrochanteric processes, the absence of a widened midsection of the synsacrum (which indicates the absence of a glycogen body), and the absence of fusion between the pelvic bones at the level of the acetabulum. The latter two features suggest that Gargantuavis is not closely related to the Ornithurae and the taxon may even fall outside the Ornithothoraces, the clade including Enantiornithes and Ornithuromorpha. Recognition of Gargantuavis in the fauna of the Hat¸ eg Island is of particular significance, because various theropods have been described from the Upper Cretaceous of Romania. The Romanian pelvis is of similar size to Elopteryx nopcsai, which was described as avian and is based on hindlimb elements, and it also shows some similarities to the pelvis of the unusual theropod Balaur bondoc. The new fossil furthermore disproves the hypothesis that the flight capabilities of Gargantuavis were lost in an insular environment of the Ibero-Armorican Island, and raises the possibility that Gargantuavis, Elopteryx, and Balaur belong to a distinctive theropod clade of the Late Cretaceous European archipelago.
