Search results for "TECTONICS"

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…

The extensional Messaria shear zone and associated brittle detachment faults, Aegean Sea, Greece

2005

Structural, thermochronological and metamorphic data are used to elucidate the tectonic nature and evolution of the ductile extensional Messaria shear zone and the associated brittle Messaria and Fanari detachment faults, which exhumed their footwall from mid-crustal depths on the island of Ikaria in the Aegean. Thermobarometric data indicate that the Messaria shear zone formed at 350–>400 °C and 3–4 kbar (i.e. at a depth of c . 15 km). Normal faulting was accompanied by the intrusion of two granites, which together with the thermobarometric data indicate a relatively high thermal field gradient of 25–35 °C km −1 . Zircon and apatite fission-track and apatite (U–Th)/He ages demonstrate rapi…

Flow and Deformation

1998

A hunter who investigates tracks in muddy ground near a waterhole may be able to reconstruct which animals arrived last, but older tracks will be partly erased or modified. A geologist faces similar problems to reconstruct the changes in shape that a volume of rock underwent in the course of geological time, since the end products, the rocks that are visible in outcrop, are the only direct data source. In many cases it is nevertheless possible to reconstruct at least part of the tectonic history of a rock from this final fabric. This chapter treats the change in shape of rocks and the methods that can be used to investigate and describe this change in shape. This is the field of kinematics,…

Continental degassing of helium in an active tectonic setting (northern Italy): the role of seismicity

2020

AbstractIn order to investigate the variability of helium degassing in continental regions, its release from rocks and emission into the atmosphere, here we studied the degassing of volatiles in a seismically active region of northern Italy (MwMAX = 6) at the Nirano-Regnano mud volcanic system. The emitted gases in the study area are CH4–dominated and it is the carrier for helium (He) transfer through the crust. Carbon and He isotopes unequivocally indicate that crustal-derived fluids dominate these systems. An high-resolution 3-dimensional reconstruction of the gas reservoirs feeding the observed gas emissions at the surface permits to estimate the amount of He stored in the natural reserv…

Seismic moment tensors and regional stress in the area of the December 2013–January 2014, Matese earthquake sequence (Italy)

2014

Abstract The main goal of this study is to provide moment tensor solutions for small and moderate earthquakes of the Matese seismic sequence in southern Italy for the period of December 2013–January 2014. We estimate the focal mechanisms of 31 earthquakes with local magnitudes related to the Matese earthquake seismic sequence (December 2013–January 2014) in Southern-Central Italy which are recorded by the broadband stations of the Italian National Seismic Network and the Mediterranean Very Broadband Seismographic Network (MedNet) run by the Istituto Nazionale di Geofisica e Vulcanologia (INGV). The solutions show that normal faulting is the prevailing style of seismic deformation in agreeme…

A multi-methodology and sustainability-supporting framework for implementation and assessment of a holistic building renovation

La ristrutturazione degli edifici in futuro dovrà essere condotta secondo una prospettiva più olistica legata alla sostenibilità vista in una più ampia gamma di obiettivi/criteri e facilitata dagli scenari di ristrutturazione possibili. La ristrutturazione degli edifici dovrebbe servire a migliorarne le performance al fine di soddisfare le esigenze degli utenti, rendendo questi ultimi meno vulnerabili in relazione ai futuri costi energetici. Vi è un grande potenziale per ridurre il consumo di energia negli edifici esistenti. Tuttavia, ciò non deve comprometterè i valori architettonici e di qualità che rendono particolari. Pertanto, non possono essere semplicemente rinnovati, ma devono subir…

Synsedimentary-tectonic, soft-sediment deformation and volcanism in the rifted Tethyan margin from the Upper Triassic–Middle Jurassic deep-water carb…

2014

Abstract The Pizzo Lupo section (Sicanian Mts, central Sicily) is an Upper Triassic–Lower Jurassic condensed deep-water succession, where the relationships among synsedimentary tectonic, soft-sediment deformations, volcanism and lithological changes reflect the evolution of a rift-basin. The morphostructural setting of the studied basin appears as a gently dipping slope where a fault-delimited area (graben to halfgraben) was developed. The instability of the sea floor, related to the seismic shocks, was the cause of the gravity-driven deformational sedimentary structures (slumping, breccia channelized bodies). The partly stratified basaltic rocks, with disorganized and chaotic stratificatio…

Preliminary results of a geomorphological and DInSAR characterization of a recently identified Deep-Seated Gravitational Slope Deformation in Sicily …

2019

The study is part of a larger project that involves the analysis of recently identified Deep-Seated Gravitational Slope Deformation (DSGSD) in Sicily which have been sub-divided according to the geological framework in light of the new geological data about the regional setting. Here are presented the first results of a multidisciplinary study of a DSGSD recently identify in Mount San Calogero area (Northern Sicily). The study was performed by means of different approaches including conventional methods (field surveys) and the Differential Interferometry Synthetic Aperture Radar (DInSAR) technique. The geological and geomorphological analyses were carried out to investigate slopes dynamic, …