Giacomo Corti

Interaction between normal faults and pre-existing thrust systems in analogue models

Abstract The influence of pre-existing thrusts on the development of later normal faults was investigated using scaled laboratory analogue models. Experiments consisted of a phase of shortening followed by extension at variable angles of obliquity (α) to the shortening direction. Results suggest that the angle α has a major influence on the surface fault pattern and on the interaction between shortening-related structures and later extensional structures. Three different modes of interactions were identified depending upon the extension kinematics. (1) For orthogonal extension (α = 0°), shortening-related fold and thrust structures strongly influence the development of normal faults: graben structures nucleate within anticlines and the normal faults reactivate thrusts at depth (branching at depth mode of interaction). (2) For highly oblique extension (α ≥ 45°), shortening-related structures exert no influence on normal faults as extension-related steeply-dipping faults (characterized by an oblique component of movement) displace early thrusts (no interaction mode). (3) For intermediate obliquity angles (α = 15°, 30°), an intermediate mode of interaction characterizes the experiments, where the no interaction and branching at depth modes coexist in different regions of models. Modelling results can be used to infer regional extension directions as is shown for the Northern Appenines (Italy).

Ice-flow dynamics and meteorite collection in Antarctica

Abstract Typical targets for meteorite searches in Antarctica are blue ice fields in front of major bedrock obstacles, where the meteorite-bearing ice slows down, is uplifted and exhumed by ablation. However, in some areas collection occurs in the lee of topographic barriers, as documented in the downstream side of the Frontier Mountain, a major emerged bedrock barrier. In this study we present an analogue modelling study of ice flow at Frontier Mountain, which has been chosen as example study area because an exceptionally complete set of glaciological data is available to investigate the causes leading to meteorite concentration. Results of modelling show how the boundary conditions (mainly the bedrock topography) control ice flow and how this flow, coupled to high ablation, may give rise to a stable meteorite trap downstream of major topographic obstacles. Modelling results support the contention that, as erosion is not a mountain builder, ablation does not represent a driving force in ice-flow dynamics, although it plays a significant role in shaving stranding surfaces and exhuming meteorites.

Seismic hazard of the Northern Apennines based on 3D seismic sources

Seismic hazard has been computed for the Northern Apennines in northern Italy based on a new seismogenic zonation. This zonation considers inclined (dipping) planes as seismogenic sources, defined on the basis of all the seismotectonic information available so far. Although these geometries are extremely rough because they simplify with a few inclined elements the totality of faults constituting a source, this model mimics the tectonic style better than that based on horizontal planes. Nevertheless, for a comparison between the new ground motions obtained and those available in the literature, the plane version of the zonation has been developed, where horizontal areas (the standard seismogenic zones), representing the surficial projection of the inclined planes, are used as seismogenic sources.