Vladimir Lyakhovsky

A rheological model of a fractured solid

Abstract Experiments to study the behavior of various materials point to the relation that exists between elastic properties and the type of stress. The influence of the state of stress on the elasticity of a fractured material will be discussed for a physically non-linear model of an elastic solid. The strain-dependent moduli model of material, presented in this paper, makes it possible to describe this feature of a solid. It also permits to simulate a dilatancy of rocks. A damage parameter, introduced into the model using a thermodynamical approach, allows to describe a rheological transition from the ductile regime to the brittle one, and to simulate the rocks memory, narrow fracture zone creation and strain rate localization. Additionally, the model enables the investigation of the final geometry of fracture zones, and also to simulate their creation process, taking into account pre-existing fracture zones. The process of narrow fracture zone creation and strain rate localization was simulated numerically for single axis compression and shear flow.

Faulting processes along the northern Dead Sea transform and the Levant margin

The northern Dead Sea transform is markedly different from the southern segments of the transform. The strike of the transform changes in this area that forms a restraining bend, and the displacement on it is much less than that on the southern and central Dead Sea transform. The structure and evolution of the northern Dead Sea transform was simulated using a rheological model of a visco-elastic material that takes into consideration the crustal structure variations in this area and the proximity to the collisional belts along the Cyprean arc and the Taurus Mountains. The simulation can explain the formation of the restraining bend, known in this area as the Yammuneh fault, and the faulting along the northern Levant continental margin, providing that a simultaneous propagation of the Dead Sea transform from the north and south took place. This suggests that restraining bends in general, which are common features along continental transform faults, are formed when two segments of a transform propagate toward each other.

Simulation of collision zone segmentation in the central Mediterranean

Abstract Collision processes between the African and European plates in the Ionian Sea offshore Calabria and in Sicily take place in several ways. To the east, normal subduction of oceanic crust (underlying the Ionian Sea) occurs underneath the Calabrian arc, whereas to the west, continental collision between the Pelagian block and the Calabrian arc (which extends from Calabria to the northeastern tip of Sicily and offshore of the island to the north) gives rise to the Maghrebian thrust belt on mainland Sicily. This belt consists mostly of stacked basinal and platform carbonates of Mesozoic-early Tertiary age deposited along the Africa passive margin. No clear subduction characterizes the area north of the HybleandashMalta plateau where it collides with the Maghrebian chain. The origin of the HybleandashMalta plateau is unclear. Geophysical data indicate, however, that its crustal structure is different from that of the surrounding Pelagian foreland. Crustal structure variations at the edge of the subducted African plate may thus cause the observed segmentation of the collisional arc system. A computer model of the region was created to learn about the deformation and faulting processes in the region. The simulation starts prior to the collision of the Pelagian block with the Calabrian arc. With time the HybleandashMalta plateau collides with the northern crustal block and, as a result, a new simulated topography, a new distribution of velocities and, most important, a new distribution of fracture zones are created. A shear fracture zone is formed east of the HybleandashMalta plateau (Malta escarpment) extending to the subduction zone at the Calabrian arc. A less active strike-slip fracture zone is created west of the HybleandashMalta plateau. An additional E-W trending active fracture zone is creating in the southern part of the simulated area. This feature may correspond to a fault zone which runs from the Strait of Sicily to the Ionian Sea.

The origin of the Dead Sea rift

Abstract The Dead Sea rift is considered to be a plate boundary of the transform type. Several key questions regarding its structure and evolution are: Does sea floor spreading activity propagate from the Red Sea into the Dead Sea rift? Did rifting activity start simultaneously along the entire length of the Dead Sea rift, or did it propagate from several centres? Why did the initial propagation of the Red Sea into the Gulf of Suez stop and an opening of the Gulf of Elat start? Using crustal structure data from north Africa and the eastern Mediterranean and approximating the deformation of the lithosphere by a deformation of a multilayer thin sheet that overlies an inviscid half-space, the regional stress field in this region was calculated. Using this approach it is possible to take into account variations of lithospheric thickness and the transition from a continental to an oceanic crust. By application of a strain-dependent visco-elastic model of a solid with damage it is possible to describe the process of creation and evolution of narrow zones of strain rate localization, corresponding to the high value of the damage parameter i.e. fault zones. Mathematical simulation of the plate motion and faulting process suggests that the Dead Sea rift was created as a result of a simultaneous propagation of two different transforms. One propagated from the Red Sea through the Gulf of Elat to the north. The other transform started at the collision zone in Turkey and propagated to the south.

Deformation and seismicity associated with continental rift zones propagating toward continental margins

[1]xa0We study the propagation of a continental rift and its interaction with a continental margin utilizing a 3-D lithospheric model with a seismogenic crust governed by a damage rheology. A long-standing problem in rift-mechanics, known as thetectonic force paradox, is that the magnitude of the tectonic forces required for rifting are not large enough in the absence of basaltic magmatism. Our modeling results demonstrate that under moderate rift-driving tectonic forces the rift propagation is feasible even in the absence of magmatism. This is due to gradual weakening and “long-term memory” of fractured rocks that lead to a significantly lower yielding stress than that of the surrounding intact rocks. We show that the style, rate and the associated seismicity pattern of the rift zone formation in the continental lithosphere depend not only on the applied tectonic forces, but also on the rate of healing. Accounting for the memory effect provides a feasible solution for thetectonic force paradox. Our modeling results also demonstrate how the lithosphere structure affects the geometry of the propagating rift system toward a continental margin. Thinning of the crystalline crust leads to a decrease in the propagation rate and possibly to rift termination across the margin. In such a case, a new fault system is created perpendicular to the direction of the rift propagation. These results reveal that the local lithosphere structure is one of the key factors controlling the geometry of the evolving rift system and seismicity pattern.

Stress distribution over the Mozambique Ridge

Abstract The Mozambique Ridge is an aseismic oceanic plateau in the southwestern Indian Ocean. During the separation of Antarctica and South Africa in the Early Cretaceous, the Mozambique Ridge was segmented by fracture zones which were assumed to become inactive during the Cenomanian, when Africa and Antarctica were finally separated. However, the existence of active normal faulting in the central part of the Mozambique Ridge was demonstrated by single and multichannel seismic surveys. Numerical modelling of the stress distribution caused by the crustal structure of the Mozambique Ridge and the adjacent oceanic basins suggests the possible existence of a zone with average horizontal tension up to 70 MPa along the central part of this passive ridge, which may cause the modern fault activity. These stresses also cause an additional dynamic anomaly which can explain small variations of the geoid anomaly over the ridge.