Within the framework of the elastoplastic model, the development of irreversible deformation during horizontal compression of a sedimentary layer lying on a rigid foundation is considered. The influence of strength parameters of the medium and friction in the base on the configuration of plasticity zones and localization of deformation has been studied. Analytical estimates are made of the depths at which irreversible deformation develops, as well as their changes as a result of an increase in horizontal stresses. With the help of numerical simulation, the features of the origin and development of localized shear bands are shown. Schemes are constructed illustrating the nature of the development of localization bands depending on the properties of the medium.

The relevance of the research. The construction of industrial facilities in areas with difficult relief and geological structure requires calculations of the stress-strain state in order to obtain estimates of the zones of irreversible deformation development. This problem can be solved using numerical modeling. In this paper, we consider a section of the planned construction of the Volochaevskoe electric depot of the Dzerzhinsky line of the Novosibirsk subway. The difficult relief and low strength characteristics of the construction zone require special attention to assess of the soil bearing capacity and the slopes stability of closely located ravines. Numerical modeling is used to assess the stress-strain state of the medium using geophysical data on the structure and mechanical properties. These data provided information on stress concentration zones and the possible development of irreversible deformation. The main aim of the research is to determine the stress-strain state and evaluate the stability of the upper part of the geological section using petrophysical and geophysical data obtained by seismic and electrical exploration. The object: geological section along the extension section of the Dzerzhinsky line of the Novosibirsk subway of the Volochaevskoe electric depot. Methods. Numerical modeling is used to calculate the stress-strain state in the construction zone. The problem is solved in an elastoplastic setting. Geometric and geomechanical parameters of the environment are obtained in the analysis of petrophysical and geophysical data. Result. The paper considers the section of the medium crossing the construction site of the electric depot "Volochaevskoye" of the Dzerzhinsky line of the Novosibirsk subway. Two geomechanical models are introduced: the first horizontally layered built on the basis of seismic data, the second is more complex, it includes data on heterogeneities found on the basis of the electrical resistivity distribution. The study area is characterized by a general deformation associated with zones of reduced strength. They are found in a complex analysis of electrical exploration and petrophysics. The stress-strain state does not significantly change taking into account these zones. Localization zones of irreversible deformation and fracturing can be formed in the upper part of the earth's crust. It was established that zones with a sharp difference in relief represent the greatest danger and will be destroyed first.

The study devoted to the layering effect on the thrust structures formation. The layers strength properties effect on the deformation medium pattern and the stress state distribution features is studied. It is shown that a strength change due to depth leads to an inhibition of the plastic deformation localization zones development and a prerequisites creation to the internal detachment formation.

Актуальность работы.Строительство промышленных объектов на участках со сложным рельефом и геологическим строением нередко требует проведения расчетов напряженно-деформированного состояния с целью получения оценок возможных зон развития необратимой деформации. Данная задача может быть решена с помощью численного моделирования.В настоящей работе рассмотрен участок планируемого строительства электродепо «Волочаевское» Дзержинской линии Новосибирского метрополитена. Сложный рельеф и низкие прочностные характеристики зоны строительства требуют особого внимания к оценке несущей способности грунта и устойчивости склонов близкорасположенных оврагов. Применениечисленного моделирования для оценкинапряженно-деформированного состояния средыс использованием геофизических данных о ее строении и механических свойствахпозволилиполучитьинформацию о зонах концентрации напряжений и возможного развития необратимой деформации. Цель: определить существующее напряженно-деформированное состояние иоценить устойчивость верхней части геологического разреза на основе имеющихся петрофизических и геофизических данных, полученных с использованием сейсмо- и электроразведки. Объект:геологический разрез, проходящий вдоль участка продления Дзержинской линии Новосибирского метрополитена электродепо «Волочаевское». Методы.расчет напряженно-деформированного состояния грунта в зоне строительства осуществлялся при помощи численного моделирования. Задача решалась в упругопластической постановке. Геометрические и геомеханические параметры среды были получены в ходе анализа петрофизических и геофизических данных. Результаты.Рассмотрено сечение среды, которое пересекаетучасток строительстваэлектродепо «Волочаевское» Дзержинской линии Новосибирского метрополитена. Представлены двегеомеханическиемодели. Первая горизонтально-слоистая и построена на основе сейсморазведочных данных. Вторая более сложная, учитывает также данные о неоднородностях, выделенных на основе распределения удельногоэлектрического сопротивления.Показано, что для исследуемой территории характерна общая деформация, связанная с наличием зон, обладающих пониженной прочностью, которые выделяются при комплексном анализе данных электроразведки и петрофизики. Несмотря на то, что учет этих зон не привел к значимым изменениям в напряженно-деформированном состоянии среды, было показано, что в приповерхностной части земной коры возможно формирование зон локализации необратимой деформации и трещиноватости.Установлено, что зоны с резким перепадом рельефа представляют наибольшую опасность и будут разрушаться в первую очередь.

The structural features of the localized deformation bands of thrust structures in a layered medium are studied using the numerical method. We studied the influence of layers position with different rheological properties on the deformation pattern of the thrust zone and the fault structures formation. It is shown that interlayers with low strength lead to inhibition of the development of zones of localization of plastic deformation and prevent the formation of faults intersecting all layers. The strength properties of the layers can greatly change. If the underlying layer has a reduced strength, detachment may form inside the sedimentary stratum.

Changes in the earth's crustal relief in the fold-thrust belts can provide information about the features of their development and the type of friction between the sedimentary layer and the basement. The paper considered cases where friction is constant and decreases when high values of plastic deformation are achieved. Cases are considered when the sediment layer is active and moves toward the basement and when the basement moves up under the sediment. The purpose of the study is determining the differences between the models based on the change in the relief and the distribution of plastic deformation localization zones. The obtained results are compared with the theory of the critical wedge and physical experiment. The problem is solved by a numerical method in an elastoplastic formulation.

Thrust faulting has been studied within the framework of a tectonic wedge model. A variant of the model was proposed which accounts for changing friction between the wedge bottom and a rigid foundation during irreversible deformation. Some specific deformation structures typical for thrust zones were revealed; their formation conditions were estimated. The range of friction coefficient values was determined in which the friction coefficient has a general effect on thrust structures. The nucleation sites and the main patterns of fault structures were described depending on the parameters of the medium and friction conditions at the bottom. The shear bands can initiate both from the layer bottom and from the surface, at irregularities of the relief, as well as at the front of the plastic deformation zone. It was found that listric faults initiate at the layer bottom in a medium with low shear strength. In a high strength medium, shear banding starts from the wedge surface. The calculations showed that the main factors determining the overall pattern of the deformation structure and fault structure in the thrust zone are the strength characteristics of the medium and friction between the deformed layer and the rigid foundation. The deformation processes were modeled by solving a system of dynamic equations of an elastoplastic medium using an explicit numerical scheme under plane strain. The behavior of the medium was described by a model with the Drucker—Prager yield surface and non-associated flow rule, with account for hardening and softening of the medium during plastic deformation.

Представлены результаты изучения природы геофизических аномалий, наблюдаемых малоглубинными методами сейсмо- и электроразведки, с привлечением данных лабораторных измерений плотности по изменениям коэффициента петрофизической неоднородности на примере геофизических исследований в составе инженерно-геологических изысканий на участке размещения электродепо «Волочаевское» Дзержинской линии Новосибирского метрополитена. Shows the results of investigation of the geophysical anomalies to the complex of shallow geophysical methods with the use of laboratory density measurements based on the study of the petrophysical heterogeneity on measurements. Researches are conducted on the example of geophysical studies as part of engineering and geological surveys on the site of the electrodepo «Volochaevskoe» Dzerzhinsky line of the Novosibirsk subway.

The deformation problem of a wedge lying on a rigid base is considered. The effect of basal friction on the formation of thrusts is studied numerically. A model with a decreasing value of basal friction is proposed. The effect of clustering of areas with differently reduced friction was found. As a result, the friction coefficient changes periodically and it correlates with the formation of localized shear bands and stressed state. Zones with reduced friction correspond to areas with higher irreversible deformation and lower values of the ratio of \(\tau /p\). Thrust differences are shown in the case of constant and decreasing friction. In the first case, the faults are linear, and the topographic slope is consistent with the critical wedge theory. The faults have a list form when friction decreases during the deformation process. The greatest slope of the topographic surface is in the frontal zone, where shear deformation bands are formed. The slope of the topography becomes much less in the zones, where the slip occurs with low friction.

The results of numerical simulation of fault structure formation under compression are presented in the article. The influence of internal friction on the formation zone and shape was considered. It has been shown that the presence of friction at the bottom of the fold-thrust belt and restoration of strength in the containment areas of plastic deformations contribute to the advance of the deformation front along the wedge. The obtained results demonstrate great importance for further study of the nature of fault structures and their distribution in the medium.

The article presents the results of numerical calculations of deformation using an Earth's crust model fragment under the influence of gravitational force. It is shown that plastic deformation in low-strength blocks changes the stress-strain state in the medium and produces a surface deflection which is hundred meters deep. The deflection is defined by the properties of the medium, its extent, and conditions at the lateral boundaries. The order of load application beyond the elastic limit affects the development of deformation, which should be taken into account when formulating problems and performing numerical simulations. The problem has been solved using a two-dimensional elastoplastic approach.

Представлены результаты численного моделирования деформации земной коры по профилю Тарим-Алтай под действием гравитации и бокового сжатия в упругопластическом 2D-приближении. Определены условия, обеспечивающие рост гор и их корней при учёте ряда геолого-геофизических характеристик.

The results of numerical modelling of deformation of the Earth’s crust along the Tarim–Altai profile caused by the force of gravity and lateral compression using the approximate two-dimensional model of the elastoplastic transition are presented. The conditions of the formation of mountains and their roots were determined taking into account some geological and geophysical parameters.

Tectonophysical studies are conducted in South Sakhalin for identification of temporal–spatial changes in the geodynamic settings of the formation of the local structures. Analysis of the field data reveals 11 local stress state (LSS) in the large newest megastructures, which were formed on geological basement of different ages. The parameters of the tectonic stresses are significantly distinct in each LSS, especially the orientations (up to reindexation) of the compression and extension axes in different fault wings. Tectonic stresses of two ages and constant latitudinal and horizontal compression axis are reconstructed. The earlier cofold shear stress field with a horizontal and longitudinal extension axis is post-Miocene and the later stress field of the reversed fault with a vertical extension axis is orogenic. The LSSs reconstructed for the first time by the displacement vectors on slickensides, along with the data on the earthquake mechanisms, substantiate the reindexation of the horizontal extension axis with the vertical intermediate axis of major normal stresses at the postfold orogenic stage of evolution of the territory. These results are in agreement with previous data on the transformation of the dextral to reverse thrust displacements along the longitudinal fault systems. The young stress field is more confidently interpreted in the activation fault zones, which limit the orogenic blocks, whereas the traces of cofold deformations without younger orogenic stress fields better remain inside the blocks which are composed of older and strongly dislocated Mesozoic rocks.

The paper reports the numerical modeling results on the Earth's crust deformation along the Tarim-Altay profile under gravity and lateral compression. Modeling was performed to study how the strength properties and block structure of the crust section influence the formation of plastic deformation zones, day surface relief and the Moho deflection. Conditions were estimated in which mountains grow under certain geological and geophysical characteristics, including mountain root formation. The deformation process was considered in a 2D elastic-plastic formulation for the vertical section of the crust and upper mantle down to a depth of 90 km.

The inversion seismic tomography algorithm (ITS) was used to calculate 3D seismic anomalies models for velocities of P- and S-waves in the zone of the Sunda arc, Indonesia. In the area under study, strong earthquakes (M>4.8) are clustered in the zone of high P-wave velocities. Earthquake hypocenters are located in zones of both high and low velocity anomalies of S-waves. The giant Sumatra earthquake (December 26, 2004, Mw=9.0) ruptured the greatest fault length of any recorded earthquake, and the rupture started in the area wherein the sign of P-wave velo­city anomalies is abruptly changed. We calculated seismotectonic deformations (STD) from data on mechanisms of 2227 earthquakes recorded from 1977 to 2013, and our calculations show that the STD component, that controls vertical extension of rocks, is most stable through all the depth levels. In the marginal regions at the western and eastern sides of the Sunda arc, the crustal areas (depths from 0 to 35 km) are subject to deformations which sign is opposite to that of deformations in the central part. Besides, at depths from 70 to 150 km beneath the Sumatra earthquake epicentre area, the zone is subject to deformations which sign is opposite to that of deformations in the studied part of the Sunda arc. For earthquakes that may occur in the crust in the Sunda arc in the contact zone of the plates, maximum magnitudes depend on the direction of pressure imposed by the actively subducting plate, which is an additional criteria for determining the limit magnitude for the region under study.