Seismic Belts and Zones of the Earth: Formalization of Notions, Positions in the Lithosphere, and Structural Control

The problem of earthquake forecasting remains challenging, especially considering strong seismic events (M≥8). Strong earthquakes occur most often along the fault planes due to large-amplitude displacements of the contacting blocks. In such cases, the physical parameters of the earthquake foci generation process are estimated on the basis of the concepts describing the destruction of solids. In this paper, we present a new tectonophysical model of strong earthquake foci in the continental lithosphere. In this model, an earthquake focus is viewed as a body whose rheological properties are changing over time throughout the entire seismic period, including the moment of the seismic event initiation, its occurrence and the subsequent stress release in of the geological medium. In the period when a future earthquake source develops and grows, the physical properties of the host rocks are assumed to change substantially, and both the viscosity and the relative shear strength decreases. At the moment of time when a strong earthquake takes place, the viscosity of the rocks in its focus is at its minimum value and thus favorable for high-amplitude interblock shearing under the current regional stress and unchanged geodynamic factors. A decrease in the viscosity is facilitated by an increase in the fault length and leads to weakening of the geological medium and decreases its strength properties. When the earthquake occurs, the viscosity of the rocks in its source is assumed significantly lower than the dynamic viscosity of the lithosphere and not less than one or two orders below the viscosity of the interblock seismically active medium containing the source. It is most likely that at the moment of time when an earthquake takes place, the viscosity in its source is 1017–1019 Pa·s. In our approach, the parameter of viscosity is introduced into the physics of earthquake foci, and the time factor is taken into account when studying the process of earthquake preparation and occurrence, which can be an important step to gaining more knowledge for forecasting of the strongest seismic events (M≥8).

Section: сейсмический процесс как квазитечение: современные представлunclassified

The rheology of the geological medium of interblock seismically active faults in the continental lithosphere: a key to understanding the generation of the strongest earthquakes in Central Asia

Шерман

Gorbunova

2018

“…Это -«фокальный слой», «сейсмоактивный объем», «очаговый слой», «сейсмогенерирующий слой», «сейсмоактивный слой», а также «собственные структуры сейсмичности», «сейсмические пояса и зоны Земли» и т.п. [Levi, 1987a[Levi, , 1987bShebalin et al, 1987;Sherman et al, 2002;Sherman, Zlogodukhova, 2011;и др. ].…”

Section: сейсмические структуры литосферыunclassified

Heliogeodynamics and seismicity in Pribaikalie

Леви

Мирошниченко

Чечельницкий

et al. 2018

The field of earthquake epicentres of Pribaikalie (Russia) is reconstructed from the data of historical and instrumental monitoring of earthquakes. The analysis shows that seismic events in the study area are distributed irregularly in space and time. The seismic process in Pribaikalie is investigated through the prism of seismic structures in the lithosphere; the irregular occurrence of seismic events in time is considered with reference to seismic weather and climate; and the causes of periodic activations of the seismic process are discovered in relation to the external effects on the Earth's physical fields from cosmic and solar processes. It is proposed to classify the seismic structures as specific geometric objects located in the lithosphere. Such objects are viewed as abstract structural elements. Some regular features are noted in the occurrence of seismic events. It is revealed that the seismic process in time shows a similarity with the course of hydrometeorological processes, which is reflected in the periodicity of elastic energy release, if only the change in the number of earthquakes (of different energy classes) in time is analysed by years. An evidently regular time pattern of seismically active periods suggests that the seismic process is influenced by some external factors. In this study, we apply the concepts of heliogeodynamics, space climate and weather to investigate such factors.

“…В целом по этому критерию СП характеризуется постоянным преобладающим в реальном времени типом напряженного состояния литосферы. В локальных местах СП напряженное состояние может характеризоваться векторами других сочетаний, отличающихся от превалирующего типа напряженного состояния в СП [Sherman, Zlogodukhova, 2011].…”

Section: сейсмические пояса сейсмические зоныunclassified

Tectonophysical Signs of the Formation of Strong Earthquake Foci in Seismic Zones of Central Asia

Шерман¹

2016

Vibrations of the Earth crust and variations in the physical fields of the Earth atmosphere and ionosphere are continuously monitored by a variety of techniques and specialized facilities across the world. Nevertheless, most catastrophic earthquakes even in this century have occurred in "incidental" or "unexpected" places in "unpredicted" time. Earthquake predictions have errors as the current knowledge of focal mechanisms of strong (M≥8) earthquakes is still insufficient. It is believed today that the most common source of earthquakes is movement of rock blocks along a fault/megafracture. Such movements take place in a stepwise pattern with high or reduced friction, depending on the presence of fluids, hitches on the fault planes and other factors. Modern seismic forecasting is based on the concept of precursors.The author considers geological and geophysical settings in areas of dynamic influence of faults, wherein 8>М>7.5 earthquakes took place. Based on earthquake recurrence curves constructed for such areas, four tectonic criteria for formation of strong earthquake sources are identified: structural (large seismically active faults), kinematic (large amplitudes of the fault wing's displacements), rheological (physical properties of the fault infill material, such as low viscosity of the intra-fault medium) and dynamic (high rates of the fault wing's displacements) criteria. These criteria should be in the focus of quantitative studies in order to provide a solid scientific basis for long-term forecasting of strong earthquakes. Curves constructed for the criteria can show changes in the physics of earthquake foci in case of strong seismic events.With account of the tectonophysical features of faults associated with strong seismic events, the following conclusions are drawn. (1) In the continental lithosphere, catastrophic earthquakes (M≥8) occur in areas of dynamic influence of the major faults in the lithosphere in case of relatively high amplitudes of displacements of boundary blocks (i.e. fault wings). (2) In the relatively stable stress field, high amplitude displacements take place in case of reduced viscosity/quasi-viscosity of the medium comprising the internal structure of faults. (3) Reduced viscosity of the intrafault medium is related to the physical conditions of transition of rocks in fault zones (mainly along the fault planes) in the state of quasi-plastic or plastic flow (unilateral pressure in excess of hydrostatic pressure, and relatively decreasing strength properties of the intra-fault medium with increasing length of the fault wings). (4) Reduced viscosity of the fault zone leads to an increase in the displacement rate of the fault wings in the constant stress field. The latter factor is the main one, transforming seismically active faults with M≤7.5 seismic events into faults of similar characteristics, but with earthquakes of higher energy, M≥8. Focal mechanisms of such earthquakes are associated with conditions for a potential increase of the displacement amplitude regardless of the pre...