On Discrete Structure of Geologic Medium and Continual Approach to Modeling Its Movements

Abstract

This paper discusses the structure of a geologic medium represented by accessible lithified rocks and provides an overview of methods used to describe its movements. Two basic opinions are considered in the framework of the discussion: (1) an initially homogeneous and continuous geologic medium acquires the structure composed of blocks in the process of the geologic medium's deformation/destruction/degradation, and (2) a geologic medium is composed of blocks (and often has hierarchic, active, energy-saturated features), and the continuity model is thus not valid for describing the geologic medium's deformation. Proponents of the first point of view actively apply the standard or modified continuum model of a solid deformed body (SDB) in estimations of the stress-strain state, but the input parameters of this model do not contain any information on discreteness in principle. Authors who support the second opinion, either explicitly or implicitly assume that the block structure of the geologic medium, which is detectable by geological methods, makes a direct and unambiguous impact on all other mechanical properties of the geologic medium and, above all, on the nature of its movements.Based on results obtained by interpreting the data collected in our long-term field studies of rock fracturing, mathematical processing of GPS-measurements, and theoretical models, we agree with the concept of the geologic medium's block structure, but argue that the geologic block-structure property is not acquired but congenital. Regarding sedimentary rocks, it means that the discrete structure has been already embodied in the rock before sediment lithification, regardless of the intensity of macroscopic deformations. A discrete structure is the form of the geologic medium existence and a cause of the congenital anisotropy of the geologic medium's strength characteristics. Due to subsequent deformation of the geologic medium, some elements of the structure can be manifested more clearly, and the structure itself can become more complex due to secondary effects. At the same time, the structure of geologic blocks is not directly manifested in the spatial and temporal features of the recent movements in the geologic medium. However, it is not an obstacle to developing continuum models of such movements in the same way as, for instance, the adequacy of the continuum general theory of relativity is not denied in view of the discrete-hierarchical structure of the Universe.The key requirements to a model include its applicability, testability, confirmability/deniability of its predictions in the investigated space-time scale, and compliance with conservation laws. This paper briefly discusses the most important aspects of the continuum approach based on the concept of an effective continuous medium and, above all, the Cauchy continuum model, envisaging that the dynamic response of the medium in spatial descriptions is given only by the Cauchy symmetric stress tensor (T). In more general continuum models of the medium (such as mom...

On the genesis of the 2013 Bachat earthquake

“…Cоглашаясь с позицией Ш.А. Мухамедиева [Mukhamediev, 2016] о том, что «…этот термин плохо определен и поэтому потенциально вредоносен..», отметим, тем не менее, что нет основания полагать, что «энергонасыщенность» (плотность энергии, потенциальная энергия системы и т.п.) увеличивается в результате действия массового взрыва.…”

Tectonics of rock loosening: geological data and physics of the process

“…Совмещение этих двух подходов увеличивает вероятность правильного истолкования механизмов и физической сущности структурно-геологических процессов, происходящих в земной коре. Значительные успехи достигнуты в изучении геомеханики разломов [Adushkin et al, 2016;Kocharyan, 2016;Kuzmin, 2014;Mukhamediev, 2016;Rodionov et al, 1986;Ruzhich,1997;Sadovsky et al, 1988;Seminsky, 2003;Sherman, 2014;Sherman et al, 1991Sherman et al, , 1992Sherman et al, , 1994, которые охватывают весь спектр хрупкой деформации от внутрикристаллических микротрещин до трансконтинентальных разломных зон, однако при этом и в геологии, и в геомеханике меньше внимания уделяется 3D-деформации геологических тел, не связанной непосредственно с разломами или с зонами их влияния.…”