Carlo Giunchi

Plio‐Quaternary vertical motion of the Northern Apennines: Insights from dynamic modeling

We test the effects of different geodynamic mechanisms on the Pliocene to present-day dynamics, and in particular on the vertical motions, of the Northern Apennines system by means of two-dimensional finite element models. We show that the Pliocene features of the Northern Apennines (exhumation of deep rocks in western Italy and fast subsidence rates in the Adriatic foredeep) can be adequately reproduced by a model (SLAB) characterized by the passive sinking of a negatively buoyant Adriatic slab and by the upwelling of buoyant asthenosphere beneath western Italy. Model SLAB is, however, not able to account for the Quaternary and present-day pattern of vertical motion of eastern Italy and of the Adriatic basin. A deep configuration of the system characterized by a detached slab (model DETACH) may explain the vertical motions of these areas, constrained by uplift of the eastern portions of the Apenninic chain, by an eastward shift of the foredeep depocenter and by lower subsidence rates in the Adriatic basin. The tectonic and stratigraphic data showing major differences between the Tertiary and the Quaternary evolution of the Northern Apennines are discussed.

Postglacial rebound in a non‐Newtonian spherical Earth

Using finite-elements we study the postglacial rebound in an axisymmetric Earth with a non-Newtonian rheology. Our approach allows for the first time a self-consistent study of the effect of a power-law creep on the long-wavelength deformations, which cannot be performed using flat models. We show that, for a non-Newtonian upper mantle, the time-variations of the low-degree Stokes coefficients become largely insensitive to the viscosity of the lower mantle. This is in contrast with previous evidence based on Newtonian models, which emphasized the importance of the low degree signatures for constraining the lower mantle viscosity.

Near-field propagation of tsunamis from megathrust earthquakes

We investigate controls on tsunami generation and propagation in the near-field of great megathrust earthquakes using a series of numerical simulations of subduction and tsunamigenesis on the Sumatran forearc. The Sunda megathrust here is advanced in its seismic cycle and may be ready for another great earthquake. We calculate the seafloor displacements and tsunami wave heights for about 100 complex earthquake ruptures whose synthesis was informed by reference to geodetic and stress accumulation studies. Remarkably, results show that, for any near-field location: (1) the timing of tsunami inundation is independent of slip-distribution on the earthquake or even of its magnitude, and (2) the maximum wave height is directly proportional to the vertical coseismic displacement experienced at that location. Both observations are explained by the dominance of long wavelength crustal flexure in near-field tsunamigenesis. The results show, for the first time, that a single estimate of vertical coseismic displacement might provide a reliable short-term forecast of the maximum height of tsunami waves.

The role of subduction on the horizontal motions in the Tyrrhenian Basin : a numerical model

The horizontal motions in the Tyrrhenian basin and surrounding chains, induced by subduction along the Calabrian Arc and Northern Apennines, are analyzed by means of numerical models based on finite element techniques. The driving mechanism, in 2-dimensional vertical cross-sections perpendicular to the trench, is the slab-pull due to the negative buoyancy of a stratified viscoelastic plate that models the Ionic oceanic lithosphere or Adriatic plate sinking in the upper mantle. For the modern tectonic setting of the area, we test the sensitivity of extension in the back-arc and of roll-back of the overriding plate to variations in the viscosity structure and in the geometry of subduction. Our results are compared with extensional velocities inferred from geology and SLR-VLBI data.

Basal drag and laterally varying lithosphere: implications for sea-level fluctuations and intraplate deformation

Abstract For plates drifting with respect to the highly viscous lower mantle and transition zone, we study the potential implications of lateral variations in the thickness of the lithosphere on sea level fluctuations and surface topography, horizontal intraplate deformation and stress accumulation. The lithosphere and upper mantle are described by a viscoelastic Maxwell rheology within the framework of a finite element scheme. Heterogenous lithospheric structures, appropriate for cratons and “Mariana type” subductions, are modeled in 2D vertical cross sections. The whole set of geophysical and geological signatures is highly sensitive to lateral viscosity contrasts which interact with the upper mantle flow induced by the relative velocity of the plates with respect to the lower mantle. In concert with the other driving forces of plate tectonics, the mechanism considered in this paper can be a valuable contributor to sea-level changes on geologic time scales. Viscous drag at the base of a laterally varying lithosphere can also contribute to the evolution of back-arc basins and to the explanation of the largest angle of subduction in west-dipping slabs.

Viscous drag and lateral viscosity heterogeneities: implications for intraplate deformation

We consider the effects of lateral variations in the thickness of the lithosphere on surface topography, horizontal intraplate deformation and stress accumulation for plates that drift with respect to the highly viscous lower mantle and transition zone. The lithosphere and upper mantle are described by means of a viscoelastic Maxwell rheology. A finite element scheme allows us to deal with large viscosity contrasts in the vertical and horizontal directions. Heterogeneous lithospheric structures appropriate a «Mariana type » subduction is modeled in a vertical cross sections. The dynamic topography and intraplate deformation, maintained by constant horizontal forces applied at the edges of the drifting plate, are extremely sensitive to lateral viscosity contrasts which interact with the upper mantle flow induced by the relative velocity with respect to the lower mantle. In concert with the other driving forces of plate tectonics the mechanism considered in this paper should be considered a valuable contributor to the evolution of back-arc basins and to the explanation of the largest angle of subduction in west-dipping slabs