A principal objective of my research is to understand interplay between crustal and mantle dynamics and surface processes by means of theoretical and experimental studies. My approach is three-pronged. 1: I study geophysical phenomena on the basis of available observations. 2: I develop mathematical and numerical methodologies to model geodynamic processes (such as deformations and stresses in and around the descending lithosphere) or fluid flow (such as lava flow); thermal convection in the mantle; sedimentary basin evolution and salt diapirism; and gravitational, thermal and buckling instabilities of geological structures. 3: I test model predictions against observations and explain specific features of the processes and phenomena.
When nature unleashes itself (resulting in earthquakes, volcanic eruptions, lava flows, landslides or tsunami), it strikes where and when it decides. Extreme events strike without warning and cause devastation in loss of human life and environmental damage. There is no doubt that man will never be able to prevent these occurrences entirely. However, geoscientists can gain a better understanding of the complex mechanisms behind the geohazards, dynamics of the lithosphere and its surface manifestations. Convolving the knowledge of physical processes with the knowledge of vulnerability and exposure we can construct a map of risks alerting policymakers and society on disaster risk reduction.
As a geophysicist, I interest it to understand a complex dynamic behavior of the Earth. As an applied mathematician, I interest it to bring formalism to Earth sciences. As a habitant of our planet, I interest it to know how to cope with disasters.
Surface temperature of lava can be extracted from the satellite measurements, e.g. from LANDSAT 7 ETM+ thermal and infrared bands.
Reconstruction of the lava temperature (a) and the flow velocity (c) after 20 and 80 iterations. The relevant residuals of the temperature (b) and the velocity (d) indicate the quality of the reconstruction.
Spreading lava with a ruptured crust.
A model of lava flow in a channel with ruptured crust (moving rafts are blue, and landed are red).
The Tibetan plateau and Himalayans have resulted from the continuous Indian and Eurasian plate convergence following their initial collision at about 55 million years ago. Earthquakes in the region occur mainly in response to the crustal motion and stress localization associated with this convergence. To understand the basic features of the motion and seismicity in the Tibet-Himalayan region, I develop a model of its block-and-fault dynamics. The model structure is composed of twelve interacting upper crustal blocks separated by fault planes. I develop several sets of numerical experiments constrained by the regional seismic observations, geodetic and geological data. Synthetic large events in the numerical experiments are clustered mainly on the fault segments associated with the Himalayan Frontal Thrust as well as at some internal faults of the Tibetan plateau. The clustering of earthquakes at some fault is a consequence of dynamics of the regional fault system rather than that of the fault only. I show that variations in the relationship of magnitude to frequency of the events depend on changes in the motion of the upper crustal blocks and on the rheological properties of the lower crust and fault zones. I demonstrate that the predicted crustal motion in the region is characterized by the north-northeastern movement of India toward Eurasia. Fluctuations in rheological properties of fault plane zones and/or the lower crust influence displacement rates of the crustal blocks and hence slip rates at the faults separating the blocks. This can explain the discrepancies in estimates of slip rates at major faults in the region (e.g., Altyn Tagh, Karakorum) over short and long time scales.
The research activity will address most important processes occurring in SBSBs: thermal and structural evolutions of the basins. In applications they are referred to as a maturity of hydrocarbons, their migration paths, deformations of sedimentary layers, and stresses regime. I intend to study thermo-mechanical restoration models for Pricaspian salt basin (East European platform), which plays an important role in hydrocarbon explorations and exploitations. The goal of the intended research is to understand the interplay between geodynamic, geothermal, and tectonic processes involved in the evolution of the SBSB. The specific objectives of the research are (i) to develop a 3D numerical approach to structural restoration of SBSBs; (ii) to develop a 3D numerical approach to thermo-mechanical restoration of SBSBs, and hence to determine temperatures within the basins in the geological past based on their present-day estimations; and (iii) to analyze the evolution of the Pricaspian basin using thermo-mechanical restoration models and geological and geophysical observations.
To restore quantitatively the seismically detected mantle structures and temperature field, we need a numerical tool for solving an inverse problem of thermal convection at infinite Prandtl number. I develop a variational approach to three-dimensional numerical restoration of thermoconvective mantle flow. The approach is based on a search for the mantle temperature and flow in the geological past by minimizing differences between mantle temperature derived from seismic velocities (or their anomalies) and temperature predicted by forward models of mantle flow. The mantle temperatures and flow fields in the past so obtained could be employed as constraints on forward models of mantle dynamics.
Numerical studies of ductile deformations induced by salt movements have, until now, been restricted to two-dimensional modeling (2D) of diapirism. I study several 3D models of salt diapirism and deformation of overlying sediments. We analyze a model of salt diapirs that develop from an initial random perturbation of the interface between salt and its overburden and then restore the evolved salt diapirs to their initial stages. An evolutionary model of a 2D salt wall loaded by a 2D clinoform of sediments predicts a decomposition of the salt wall into 3D diapiric structures when the overburden of salt is supplied by 3D syn-kinematic wedge of sediments. Also we study how lateral flow effects the evolution of salt diapirs. The shape of a salt diapir can be very different, if the rate of horizontal flow is much greater than the initial rate of diapiric growth solely due to gravity.
To understand processes of stress generation in the descending slab, I analyze tectonic stress in the slab by means of analytical and numerical modeling. I have found that the maximum shear stress migrates from the upper plane of the Benioff-Wadati seismic zone to its lower plane in course of changes in slab dynamics from its active subduction through roll-back movements to passive sinking solely due to gravity. It can explain a location of hypocenters of Vrancea events at the side of slab adjacent to the Eastern European platform. To understand processes of stress generation, I analyze the tectonic stress induced by the sinking Vrancea slab employing 3D Eulerian FEM and using (as input model data) seismic tomographic high-resolution images of the Vrancea lithosphere, results of refraction seismic study, and other geophysical and geological data. On the basis of experimental data on elastic parameters and anelasticity I obtain initially a model of mantle temperature from the P-wave velocity anomalies; crustal temperature is derived from heat flow data. Based on temperature- and pressure-dependent viscosity and density, modeled tectonic stress predicts horizontal compression beneath the Vrancea region, which coincides with the stress regime defined from fault-plane solutions for intermediate-depth earthquakes. The stress reaches maximum at depths of 70 to 110 km and 130 to 180 km and decays below being in a good agreement with the observed seismicity.
The juxtaposed contraction and extension, a long-standing geological enigma recognized in different geodynamic frameworks world-wide, observed at the surface and active nowadays, hence better studied, only in the Italian Peninsula, has for a long time attracted the attention of geoscientists. Several models, invoking mainly external forces, have been put forward to explain the close association of these two end-member deformation mechanisms clearly observed by geophysical, geodetic and geological investigations. These models appeal to interactions along plate margins or at the base of the lithosphere such as back-arc extension or shear tractions from mantle flow or to subduction processes such as slab roll back, retreat or pull and detachment. On the basis of seismic images of the lithosphere beneath the central Apennines and numerical modeling of lithosphere dynamics and in-situ stress, I find that buoyancy forces can explain solely the present-day stress distribution in the Apennine lithosphere, complex lithospheric deformations, and unusual earthquake distribution.
The backstripping method that is widely used in basin analysis sometimes fails for salt-bearing basins, because the highly mobile and buoyant salt deforms its sedimentary overburden. I developed a new numerical approach for two-dimensional dynamic restoration of cross-sections through successive earlier depositional stages. Our models interpreted basin profiles as multiple ductile layers with various physical parameters (e.g., density, viscosity, Young’s modulus). The evolution of salt structures was modeled backwards in time by removing successively younger layers and restoring older layers and any diapirs to the stage they were likely to have been. The applicability of the technique was demonstrated by reconstructions of upbuilt and downbuilt diapirs. I used the technique to restore a depth-converted seismic cross-section through the south-eastern part of the Pricaspian salt basin . Mature salt diapirs in the section are shown to have been downbuilt from a salt layer with an initially uniform thickness, as a result of differential sedimentary loading until the end of the Triassic before one of the diapirs was buried and actively upbuilt. Our approach is well suited for restoration of cross-sections with ductile overburdens and now is being developed to three-dimensional restorations and other rheologies.
I investigated the gravitational and buckling instabilities of a structure consisting of a buoyant layer of viscous fluid overlain by a dense perfectly plastic layer. The structure is subject to either horizontal extension or shortening and models rocksalt under a brittle overburden. Considering the viscosity of the buoyant layer to be much less than the effective viscosity of the overlying layer, we obtained the following results. The instability pattern of the structure is similar to that of a perfectly plastic structure. The characteristic wavelength, corresponding to the most unstable mode, increases initially with the thickness ratio between the lower and upper layers, but then decreases by a series of abrupt jumps. This is in contrast to the result that the characteristic wavelength approaches to a constant value with the increasing thickness ratio in the case of viscous layers. The buckling instability induced by rapid horizontal straining overwhelms the gravitational instability, and the growth rate of the instability depends linearly on the effective viscosity ratio. We studied models of diapirism in the Great Kavir, Iran. We show that a small interdiapir spacing in the salt canopy province and a wide range of the spacings in the salt pillow province of the region can be explained by the perfectly plastic sedimentary overburden and horizontal shortening.
I examined the effects of viscous flow, phase transition, and dehydration on stress in a relic slab to explain the intermediate-depth seismic activity in the Vrancea region. I developed a two-dimensional finite-element model of a slab gravitationally sinking in the mantle which predicts (i) downward extension in the slab as inferred from the stress axes of earthquakes, (ii) the maximum stress occurring in the depth range of 70 km to 160 km, and (iii) a very narrow area of the maximum stress. The depth distribution of the annual average seismic energy released in earthquakes has a shape similar to that of the depth distribution of the stress in the slab. Estimations of the cumulative annual seismic moment observed and associated with the volume change due to the basalt-eclogite phase changes in the oceanic slab indicate that a pure phase-transition model cannot explain solely the intermediate-depth earthquakes in the region. We consider that one of realistic mechanisms for triggering these events in the Vrancea slab can be the dehydration of rocks which makes fluid-assisted faulting possible. The approach can be applied to other regions of intermediate-depth seismicity.
I studied a numerical model of block-and-fault dynamics of the lithosphere beneath the earthquake-prone Vrancea region. The model presents a system of absolutely rigid blocks separated by infinitely thin plane faults. The interaction of the blocks along the fault planes and with the surrounding medium is assumed to be a viscoelastic. Motions of boundary blocks cause the displacements of the block system. The velocities of the motions are found from a model of mantle flows induced by a sinking slab beneath the Vrancea region. When a ratio of stress to pressure for some portion of a fault plane exceeds a certain strength level, a stress-drop ('earthquake') occurs. As a result of the numerical simulations catalogues of synthetic earthquakes are produced. Several numerical experiments for various model parameters illustrate that the spatial distribution of synthetic events is significantly sensitive to the directions of the block movements. Small variations in a slab rotation control the pattern of the synthetic seismicity. The results of the analysis indicate that the catalogues obtained by the simulation of the block structure dynamics have certain features similar to those of the real earthquake catalogue of the Vrancea region. The results are in a good agreement with recent seismic tomography data.
I developed a new two-dimensional Eulerian finite element methodology to study geodynamical problems where chemical composition changes abruptly across interfaces. The method combines a Galerkin-spline technique with a method of integration over regions bounded by advected interfaces to represent discontinuous variations of material parameters. It allows to directly approximate a natural free surface position, instead of a posteriori calculation of topography from the normal stress at the upper free-slip boundary. The suggested approach avoids the difficulties due to material discontinuities at intermediate boundaries, like Moho or the earth's surface, and is also free from the deficiencies of the Lagrangian approach always resulting in mesh distortion. Also I developed new three-dimensional methods for study of lithospheric deformation and mantle convection. Special computer codes were written for parallel supercomputers with distributed memory.