Search results for "Geophysics"
showing 10 items of 2645 documents
Influence of wall-to-floor connections and pounding on pre- and post-diction simulations of a masonry building aggregate tested on a shaking table
2023
AbstractThis paper presents numerical simulations within the frame of the project SERA—AIMS (Seismic Testing of Adjacent Interacting Masonry Structures). The study includes blind pre-diction and post-diction stages. The former was developed before performing the shaking table tests at the laboratory facilities of LNEC (Lisbon), while the latter was carried out once the test results were known. For both, three-dimensional finite element models were prepared following a macro-modelling approach. The structure consisted of a half-scaled masonry aggregate composed by two units with different floor levels. Material properties used for the pre-diction model were based on preliminary tests previou…
Simulation of blind pre-diction and post-diction shaking table tests on a masonry building aggregate using a continuum modelling approach
2023
AbstractMasonry buildings of historical centres are usually organized within aggregates, whose structural performance against seismic actions is challenging to predict and constitutes still an open issue. The SERA—AIMS (Seismic Testing of Adjacent Interacting Masonry Structures) project was developed to provide additional experimental data by testing a half-scale, two-unit stone masonry aggregate subjected to two horizontal components of dynamic excitation. In this context, this paper investigates the reliability of the modelling approach and the assumptions adopted to generate a three-dimensional continuum finite element model. The work involves two stages, namely a blind pre-diction and a…
Dissimilarity Measures for the Identification of Earthquake Focal Mechanisms
2013
This work presents a study about dissimilarity measures for seismic signals, and their relation to clustering in the particular problem of the identification of earthquake focal mechanisms, i.e. the physical phenomena which have generated an earthquake. Starting from the assumption that waveform similarity implies similarity in the focal parameters, important details about them can be determined by studying waveforms related to the wave field produced by earthquakes and recorded by a seismic network. Focal mechanisms identification is currently investigated by clustering of seismic events, using mainly cross-correlation dissimilarity in conjunction with hierarchical clustering algorithm. By…
Shake-table testing of a stone masonry building aggregate: overview of blind prediction study
2023
Bulletin of earthquake engineering (2023). doi:10.1007/s10518-022-01582-x special issue: "Adjacent Interacting Masonry Structures"
On the hydro-mechanical behaviour of remoulded and natural Opalinus Clay shale
2016
The geo-energy sector makes use of advanced technologies such as shale gas extraction, CO2 sequestration and nuclear waste geological disposal that rely on the exploitation of shale formations. Due to the great depths involved in these applications and the difficulties in retrieving intact samples, remoulded shale specimens are often adopted for hydro-mechanical testing. Remoulded and intact shales may substantially differ in their hydro-mechanical behaviour due to the particular structure of the natural material, which is the result of diagenesis and burial history. This paper presents an experimental campaign aimed at (i) characterizing the role of diagenesis and depth for Opalinus Clay s…
Quantification and visualization of finite strain in 3D viscous numerical models of folding and overthrusting
2020
Abstract Finite strain analysis and three-dimensional (3D) numerical modeling are important methods to understand the deformation history of rocks. Here, we analyze finite strain in 3D numerical simulations of power-law viscous folding and overthrusting. Simulations with different and laterally varying detachment geometries cause a lateral transition from folding (for thicker detachments) to overthrusting. We compute the 3D finite strain tensor, the principal strain values and their orientations. We compute the Nadai strain, e S , and the Lode’s ratio, ν , representing the strain symmetry (constriction or flattening). We apply Hsu diagrams to visualize strain distribution in e S - ν space, …
Granular packings and fault zones
2000
The failure of a two-dimensional packing of elastic grains is analyzed using a numerical model. The packing fails through formation of shear bands or faults. During failure there is a separation of the system into two grain-packing states. In a shear band, local ``rotating bearings'' are spontaneously formed. The bearing state is favored in a shear band because it has a low stiffness against shearing. The ``seismic activity'' distribution in the packing has the same characteristics as that of the earthquake distribution in tectonic faults. The directions of the principal stresses in a bearing are reminiscent of those found at the San Andreas Fault.
Transition from thin- to thick-skinned tectonics and consequences for nappe formation: Numerical simulations and applications to the Helvetic nappe s…
2015
Abstract We use two-dimensional numerical simulations to study the deformation style and the formation of nappes during the shortening of basement–cover systems with half-grabens. We perform simulations with only linear and power-law viscous rheology, and also thermo-mechanical simulations with viscoelastoplastic rheology and temperature-dependent viscosities. The accumulated, area-averaged strain is calculated for the sediments, es, and for the basement, eb, to quantify the deformation style. The results show that the transition from thin-skinned dominated (es/eb > 1) to thick-skinned dominated (es/eb ≤ 1) deformation is controlled by two effective viscosity ratios: the ratio of viscosity …
Tonalite sill emplacement at an oblique plate boundary: northeastern margin of the Bohemian Massif
1997
Abstract A tonalitic sill has been examined at the Variscan transpressive boundary of the Lugian and Silesian plates at the NE margin of the Bohemian Massif. A structural, petrological and geochronological study reveals that it was emplaced syn-tectonically with major ductile shearing in lower crustal rocks. Magmatic and pre-rheological critical melt percentage (RCMP) fabrics are concordant with the hanging wall structures but discordant with those of the footwall. The AMS study shows the predominance of flattening strain at the margins and plane strain fabrics in the core. Numerical modelling of AMS fabrics is in good agreement with the hypothesis of magma flow and deformation in oblique t…
An exceptional rocky shore preserved during Oligocene (Late Rupelian) transgression in the Upper Rhine Graben (Mainz Basin, Germany)
2012
The Early Oligocene (Late Rupelian) Alzey Formation (Mainz Basin, Upper Rhine Graben, Germany) records the development of a rocky coast depositional system during transgression. The formation unconformably overlies Permian bedrock across a composite transgressive ravinement surface. Exposure of the surface shows a succession of subplanar bedrock terraces, separated by near-vertical risers. Terraces show a broad staircase geometry and display wave-erosional features (notches, sea stacks, furrows). Detailed sedimentological and palaeoecological investigations reveal prograding beachface and shoreface depositional units that overlie terraces and are adjacent to risers. Terraces are interpreted…