Three-dimensional forward and backward modelling of diapirism: numerical approach and its applicability to the evolution of salt structures in the Pricaspian basin

Numerical studies of ductile deformations induced by salt movements have, until now, been restricted to two-dimensional (2D) modelling of diapirism. This paper suggests a numerical approach to model the evolution of three-dimensional (3D) salt structures toward increasing maturity. This approach is also used here to restore the evolution of salt structures through successive earlier stages. The numerical methodology is applied to study several model examples. We analyse a model of salt diapirs that develop from an initial random perturbation of the interface between salt and its overburden and restore the evolved salt diapirs to their initial stages. We show that the average restoration errors are less than 1%. An evolutionary model of a 2D salt wall loaded by a 2D pile of sediments predicts a decomposition of the salt wall into 3D diapiric structures when the overburden of salt is supplied by 3D synkinematic wedge of sediments. We model salt extrusion feeding a gravity current over the depositional surface and estimate an average rate of extrusion and horizontal velocity of salt spreading. Faulting of the overburden to salt overhangs initiates new secondary diapirs, and we analyse the growth of these secondary diapirs. We also 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. We discuss the applicability of the results of the models to the evolution of Late Permian salt structures in the Pricaspian basin (Russia and Kazakhstan). These structures are distinguishable into a variety of styles representing different stages of growth: salt pillows, diapirs, giant salt massifs, 2D diapiric walls and 3D stocks complicated by large overhangs. The different sizes, shapes and maturities of salt structures in different parts of the Pricaspian basin reflect areal differences in salt thickness and loading history. Our results suggest that the numerical methodology can be employed to analyse the evolution of all salt structures that have upbuilt through younger ductile overburdens.     

Erratum to: 3D Numerical Modeling of the Summit Lake Lava Flow,Yellowstone, USA

Izvestiya, Physics of the Solid Earth - An Erratum to this paper has been published: https://doi.org/10.1134/S1069351321120016     

Geothermal evolution of the Astrakhan Arch region of the Pricaspian basin

The Astrakhan Arch region contains one of the largest sub-salt structures of the Pricaspian basin, where perspectives for hydrocarbon generation and accumulation in the Devonian to Carboniferous deposits are considered to be high. The paper addresses the problem of structural and geothermal evolution of the region deformed by salt movements. Initially, we developed a model of the regional structural evolution along a geological profile using the volume-balancing and back-stripping methods and geological constraints on the sedimentation, erosion, and paleo-water depths. Then we developed geothermal models (along the study profile) associated with the regional structural evolution. The models were constrained by the temperatures measured in four deep boreholes along the profile. We show that the present temperatures and heat flux are influenced by the presence of salt diapirs. Since the Early Carboniferous and till Middle Permian times, the temperatures predicted by the models vary significantly due to the regional transgression and the presence of seawater. The temperature of Devonian–Carboniferous carbonates increases since the Late Permian (time of post-salt deposition) and attains its maximum values in the SW-part of the profile. If the model assumptions concerning the constant vertical and zero lateral heat fluxes are valid, we can conclude that hydrocarbons are most likely to be generated in the SW-part of the region for the post-Early Permian time.     

3D Numerical Modeling of the Summit Lake Lava Flow,Yellowstone, USA

Izvestiya, Physics of the Solid Earth - Abstract—Volcanic eruptions belong to the extreme events that change the Earth’s landscape and affect global climate and environment. Although...     

Extrusion and gravity current of a fluid: Implications for salt tectonics

Numerical models of the extrusion and gravity current of a viscous incompressible fluid are studied to determine the shapes of salt structures formed on the Earth’s surface and the velocities of rock salt extrusion and lateral spreading. Two main types of salt extrusion are examined. In the case of active extrusion, salt rises to the surface at a velocity of about 30–35 cm/yr, forming a salt dome about 550 m in height. In the case of passive extrusion, the velocity of salt extrusion from under a newly developing sedimentary minibasin is significantly lower. In the course of its evolution, the salt dome becomes topographically lower and transforms into a broad plateau. The extrusion velocity of salt controls the shape, size, and velocity of its gravity current. The shapes of salt domes modeled in this study agree well with observations. The gravity current velocities in the models vary from 3 m/yr to 60 cm/yr, depending on the proximity to the current orifice. Numerical modeling of salt extrusion and gravity current in various geodynamic settings can be used for a detailed analysis of the geological and geophysical evolution of structures containing salt layers and the related oil and gas fields.     

t*— an unsuitable parameter to characterize anelastic attenuation in the Eastern Carpathians

Investigation of teleseismic P -wave recordings at a temporary network in the Eastern Carpathians, equipped with predominantly short-period sensors, is compared with synthetic modelling of anelastic attenuation of teleseismic waves in the upper mantle. Using the t * approach, we examine variations of amplitude decrease over frequency for teleseismic recordings in the frequency band 0.5–1.5 Hz. The results reveal a consistent pattern of increased t * values in the centre of the network, in the Vrancea region at the bend of the Carpathian Arc, although the magnitude of the observed variation in t * is much higher than expected. Synthetic t * parameter computations for the same event-receiver configurations reproduce the observed pattern in terms of relative variations. However, the amplitude of the synthetic t * values explains only 10–20 per cent of the observed variation in t *. t * is not a direct measure for anelastic attenuation but rather for a combination of anelastic and other attenuating effects such as scattering and amplitude fluctuation related to velocity inhomogeneities. If regional amplitude variations are solely attributed to anelastic attenuation, all other effects are mapped into Q . We discuss the role of anelastic attenuation and other effects in the case of the Eastern Carpathians and conclude that t * is an unsuitable parameter to characterize anelastic attenuation in the Eastern Carpathians.     

Preventive disaster management of extreme natural events

Several recent extreme natural events resulted in great humanitarian tragedies because of weak preventive disaster management. Here we analyze several factors (natural, economical, political, awareness, and preparedness) that brought about the humanitarian tragedies of the early 21st century. We discuss then the role of science in the preventive disaster management of extreme natural events.