O. Caselles

Modelling seismites with a digital shaking table

Abstract Soft-sediment deformation structures induced by seismically triggered liquefaction and/or fluidization (seismites) have been reproduced with a digital shaking table. We have used natural sediments with variable granulometric ranges (clay, silt and sand) and an earthquake simulator that is able to reproduce real tridimensional seismograms. Acceleration and pore pressure recording allowed us to follow liquefaction and/or fluidization processes in unconsolidated sediments during earthquakes. Different types of seismites were produced by variations in the tested sedimentary column.

GPR survey to confirm the location of ancient structures under the Valencian Cathedral (Spain)

This paper describes the ground-penetrating radar (GPR) survey performed inside the Cathedral of Valencia, Spain. It is part of historical studies performed in the Cathedral in order to add information to old maps and documents in the Cathedral Archives and also to analyze the extent and importance of potentially destructive moisture areas that were appearing on the floor. The construction of the Cathedral of Valencia occurred in three stages, all of which are well-documented in the Cathedral Archives with detailed drawings, maps, and charts. The radar data were successful in locating crypts, ossuaries, sepulchers, and graves, and the location of ancient walls that existed before the final Cathedral expansion. Three cultural layers corresponding to the three periods of construction were also identified corresponding to the Roman, Arabian and Middle Age Epochs. Measurements of relative sub-floor moisture were obtained by comparing dielectric permittivity changes and radar velocity differences between materials in humid and non-humid areas.

Assessment of Complex Masonry Structures with GPR Compared to Other Non-Destructive Testing Studies

Columns are one of the most usual supporting structures in a large number of cultural heritage buildings. However, it is difficult to obtain accurate information about their inner structure. Non-destructive testing (NDT) methodologies are usually applied, but results depend on the complexity of the column. Non-flat external surfaces and unknown and irregular internal materials complicate the interpretation of data. This work presents the study of one column by using ground-penetrating radar (GPR) combined with seismic tomography, under laboratory conditions, in order to obtain the maximum information about the structure. This column belongs to a “Modernista” building from Barcelona (Spain). These columns are built with irregular and fragmented clay bricks and mortar. The internal irregular and complex structure causes complicated 2D images, evidencing the existence of many different targets. However, 3D images provide valuable information about the presence and the state of an internal tube and show, in addition, that the column is made of uneven and broken bricks. GPR images present high correlation with seismic data and endoscopy observation carried out in situ. In conclusion, the final result of the study provides information and 3D images of damaged areas and inner structures. Comparing the different methods to the real structure of the column, the potential and limitations of GPR were evaluated.

Anelastic structure of the Iberian Peninsula obtained from an automated regionalization algorithm and stochastic inversion

Abstract An automated regionalization of a reduced domain of the Earths surface, without a-priori seismotectonic information, and the corresponding anelastic structures are achieved by means of a sequential application of a principal component analysis, a clustering procedure and the stochastic inversion algorithm to anelastic attenuation coefficients of Rayleigh waves. Our database is formed by path-averaged attenuation coefficients derived from fundamental mode Rayleigh waves crossing the Iberian Peninsula. The wavetrains were recorded at the broad-band stations installed some years ago in the Iberian Peninsula for the ILIHA project. Before the sequential application of the algorithms, the area covered by the seismic paths was characterized by 22 maps of local attenuation coefficients corresponding to the 10–120 s period range. All these maps were obtained by applying Yanovskayas formulation for laterally heterogeneous media to the set of path-averaged attenuation coefficients mentioned above. After that, we divided the Iberian Peninsula into six homogeneous regions in terms of the local attenuation coefficients for 22 different periods and by means of the principal component analysis and the clustering algorithm. We then obtained, by stochastic inversion, the respective anelastic structure down to a depth of 225 km for the six homogeneous regions. The coefficients vary from 1.0 to 2.0×10−3 km−1 and the Q−1β structures, ranging from 110×10−3 to 40×10−3, suggest for five of the regions an asthenosphere with its upper and lower boundaries close to 80 and 180 km depth, respectively. A shallow beginning of the asthenosphere is detected for the sixth homogeneous region. This range is very similar to the depths deduced from previous tomographic studies of the Iberian Peninsula based on Rayleigh wave phase and group velocities. Finally, correlations obtained between the regions and some seismotectonic characteristics of the Peninsula are discussed. It is noteworthy that we cannot associate each of the six homogeneous regions with a single Hercynian, Alpine or Neogene domain.

Characterization of a Romanesque Bridge in Galicia (Spain)

This article presents the characterization of a mediaeval bridge located in Fillaboa, Galicia (northern Spain). The study of this bridge involves data acquisition about the structure (geometry, visual inspection of damages, and nondestructive testing), the evaluation of the possible damage mechanisms compatible with the observed cracks and fissures, and the dynamic evaluation of the structure. This bridge is a masonry four-lancet arches bridge, with damage on the piers and abutments. Two non-invasive methodologies are applied to obtain information about the bridge: ground-penetrating radar (GPR) survey and ambient vibration noise measurements. The drawings of the structure were created using close-range photogrammetry (CRP). A finite elements model of the structure was obtained prior to the vibration field measurements, as a preliminary evaluation. Data obtained from GPR and the geometry determined with CRP were the information used in this preliminary model of the bridge. This model was improved using the dynamic field test to compare model behavior and to validate the numerical results. A second and more accurate model was then obtained by using finite elements according to the experimentally measured modal frequencies (the possible first three transversal vibration modes of the bridge).

Application of Particle Motion Technique to Structural Modal Identification of Heritage Buildings

Determining the behavior of a structure estimated by means of finite elements analysis requires not only an in-depth knowledge of its geometry and dynamic properties but also an experimental validation to corroborate the adequacy of the characteristics of the structure. Most of the current structural identification techniques are based on linear methods that call for many measurement points and/or a relative simple structure. Complex structures are somewhat still an unexplored field due to the difficulties with the finite element method and the experimental corroboration of its results. This study presents the use of particle motion computation applied to each structural vibration mode to improve the identification of its dynamic properties, and its application to the Gothic Cathedral of Palma de Majorca (Spain).

GPR applications in dense cities: Detection of paleochannels and infilled torrents in Barcelona GPR applications in dense cities

Barcelona is placed in a basin delimited by the Mediterranean Sea (E), the Collcerola Mountains (W) and the rivers Besos (N) and Llobregat (S). The city was built on Quaternary alluvial deposits and on the Tertiary and Palaeozoic materials of the surrounding mountains. The Quaternary materials are preponderant in the plane of the city, presenting a high lateral variability due to the paleochannels and infilled torrents existing between the Sea and the Mountains. The city was built on these heterogeneous materials. In order to prepare a detailed vulnerability map of the Barcelona city, a GPR survey provides information about the position of these geological structures. Results were compared to H/V spectral ratio measurements and soundings.

Geophysical exploration of columns in historical heritage buildings

Columns are one of the most usual supporting structures in cultural heritage buildings. This work presents the study of different columns using ground-penetrating radar (GPR) combined with seismic tomography. These columns belong to a Gothic Cathedral and to a Modernista Building. In the first case, columns are constructed with regular ashlars. GPR provide images that could define the internal ashlar distribution and shape, and the possible existence of inner cracks. However, the images must be supported with additional information from a seismic survey that could provide evidences about the stone quality. In the second case, columns are built with irregular and fragmented clay bricks, and mortar. The internal irregular and complex structure causes complicate 2D images. However, 3D images provide valuable information about the condition of the internal tube and indicate the existence of irregular elements. Results present high correlation with seismic data. In conclusion, results provide information and 3D images defining damaged areas and inner structures. Also, comparing the different methods with the structural knowledge, it is possible to define potential and limits of non-destructive testing applied to these elements.

Study of wood beams in buildings with ground penetrating radar

A large number of buildings in Barcelona city were built during the XIX Century, using wooden beams and masonry. Nowadays, these structures, some of them declared architectural heritage, suffer damages and important deterioration. Geophysical surveys by means of ground-penetrating radar could provide valuable information on the most damaged areas of the beams, and could supply useful data to improve restoration policy and heritage protection. The knowledge of the structure is needed in many cases, but often there is not information about the internal structure and the constructive techniques. However, a large number of supporting structures use to be embedded in the floor and covered by mortar, obstructing the direct visual inspection. Therefore, the access to the structure can be one of the highest difficulties in those inspections because the direct access is not possible. Hence, GPR was applied to determine internal constructive wooden elements and its state of conservation. In this work, several buildings were studied to locate damaged beams and to identify internal structures. Differences in reflections due to damaged and healthy beams appear are clearly highlighted in GPR images in several cases, while in other, differences are not so apparent.

Geological structures evaluated by means of scattering noise in ground penetrating radar images

Coastal geology in Barcelona City is formed by Quaternary sediments overlying Tertiary strata. The Quaternary plane is crossed by paleochannels and streams, all of them under the city structures and constructions. Boreholes demonstrate differences in the grain size distribution of the materials from the different geological structures. In this work, Ground-penetrating radar was proved as a tool to obtain quick information about these changes. The results from more than 20 km of GPR profiles in Barcelona city, seems to indicate that, depending on the relationship between the wavelength and grain size, GPR signal scattering increases significantly. Therefore, the analysis of the noise in GPR signals supplies information to determine the possible existence of geological changes in the quaternary deposits. Several tests and measures in well-known emplacements, as well as models and simulations, were used to determine the ability of this method in the study of the Barcelona plain shallow geology. Correlation between paleochannels and infilled streams and higher scattering noise is observed in this study. The analysis of the scattering effect on the amplitude of the radar data could help to locate paleochannels and subterranean infilled streams, being a valuable tool to improve the knowledge of the city subsoil.