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Seismicity migration is studied by a new method based on space-time diagrams and a combination of cluster and regression analyses. Data from the global and Baikal regional earthquake catalogues are analysed with the application of the specially designed geographic information system (GIS) in order to establish parameters and mechanisms of seismicity migration in space and time. We study the migration of seismic events in the following geostructural systems: the Baikal rift zone (BRZ), the area between BRZ and the Indo-Eurasian interplate collision zone, the area between BRZ and the West-Pacific seismic foci Benoiff zone, and two segments of the Middle Atlantic ridge.As evidenced by the obtained results, studying regimes of seismic migration provides for analyses of space-time distribution of seismic energy in the fault-block structure of the lithosphere and facilitates more detailed studies of the origin of deformation waves and mechanisms of the seismotectonic regime of the Earth. Forward (from the equator) and backward (towards the equator) migration of seismic events are established in all the regions under study. It is assumed that this phenomenon may result from regular changes of the polar compression of the Earth due to variations of its rotation regime. Besides, it is revealed that energy clusters of migration are regularly generated, and the regularity may be related to the 11-year cycle of the solar activity which impacts the seismic regime. We discuss the need to study the interference of wave deformations in the lithosphere which are initiated by several external energy sources. It is proposed to consider the regimes of planetary seismicity migration as a reflection of redistribution of endogenic (primarily heat) energy of the Earth during the destruction of its lithospheric shell under the impacts of cosmogenic factors via triggering mechansms. With reference to our positive experiences of applying the proposed concept to BRZ, we consider possibilities of using the seismicity migration data for prediction of earthquakes in the planetary and regional scales. Институт земной коры СО РАН, Иркутск, РоссияАннотация: Изучение процессов сейсмомиграции проводилось новым методом построения пространствен-но-временных диаграмм и посредством сочетания кластерного и регрессионного анализа. С помощью разра-ботанной геоинформационной системы (ГИС) и с использованием всемирного и байкальского регионального каталогов землетрясений решались задачи по выяснению параметров и механизмов пространственно-вре-менной миграции сейсмической активности. Сейсмомиграционные явления изучались в следующих гео- GEODYNAMICS & TECTONOPHYSICS P U B L I S H E D B Y T H E I N S T I T U T E O F T H E E A R T H ' S C R U S T S I B E R I A N B R A N C H O F R U S S I A N A C A D E M Y O F S C I E N C E S R e c e n t G e o d y n a m i c s 225E.A. Levina, V.V. Ruzhich: The seismicity migration study… структурных системах: в пределах Байкальской рифтовой зоны (БРЗ), между БРЗ и областью Индо-Евразий-ской межплитной коллизии, между ...

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The mechanics of the ice cover of Lake Baikal has been studied through monitoring of its deformation and seismic effects and full-size uniaxial compression and shear tests in 2005–2007. We measured the shear strength of ice specimens and large in situ blocks (σ = 0.2−1.9 MPa) and investigated it as a function of air temperature and ice structure. Deformation was analyzed in terms of various natural controls, such as air temperature and pressure, wind, sub-ice currents, and local earthquakes. Precise strain measurements along ice cracks were used to explore the strain behavior of ice, including the cases of dynamic failure (ice shocks). Measurements by seismic station Baikal-12 were used to monitor diurnal background microseismicity variations and to record an ice quake with its magnitude (M = 0.3–0.8; E = 104–105 J) comparable to a medium-size rock burst or a small earthquake. Ice quakes were studied in terms of their nucleation, dynamics, and aftereffects, as well as the strain and seismic responses of the ice, using sub-ice explosions in the latter case. The natural conditions of deformation in the elastoviscoplastic Baikal ice are similar to lithospheric processes and thus can be employed in tectonophysical modeling with scientific and practical implications for hazard mitigation.

Abstract:This study aims to analyze the internal structure of earthquake sources under the modern concepts in physical mesomechanics, which consider the multilevel process of faulting in the geological medium, taking into account specific features of the subsurface and deep levels of the crust. This article includes two parts that present the study results and discuss the interdisciplinary information on the subject of this study. The first part describes the subsurface crustal level, wherein seismogenic faulting takes place. We present the seismogeological data on the structure and development of the sources of three catastrophic earthquakes (М≥8.0-8.5) that occurred in Mongolia in the last century. We discuss the deep drilling (1.0-3.5 km) data on the seismodislocations formed after the recent strong and catastrophic earthquakes in the United States, Taiwan and Japan, including the zone of co-seismic fractures caused by the Tohoku-Oki earthquake (M=9.0, November 11, 2011). In the second part, jointly with specialists in petrology and geochemistry A.V. Travin and V.B. Savelieva, we will analyze the field data on the ages and the physical and chemical characteristics of geomechanical processes that took place at large depths in the fault zones, which are outcropped by the long-term denudation of the upper crustal layer in the study area. In the summary, we will describe our concepts of geomechanical and tribochemical processes taking place in the fault zones during the formation of the earthquake sources. The results of this comprehensive study give grounds to conclude that a multidisciplinary approach is needed to investigate the deep geological and geophysical processes of 'stick-slip' on the fault planes with diverse relief features in the zones wherein seismicity is generated. This conclusion is of paramount importance: it concerns the potentials of applying new approaches to forecasting, management and mitigation of seismic engineering risks arising from the hazardous effects of strong earthquakes.Key words: fault zone; earthquake source; seismodislocation; dislocation parameters; stick-slip; seismic safety GEODYNAMICS & TECTONOPHYSICS P U B L I S H E D B Y T H E I N S T I T U T E O F T H E E A R T H ' S C R U S T S I B E R I A N B R A N C H O F R U S S I A N A C A D E M Y O F S C I E N C E S T e c t o n o p h y s i c s RESEARCH ARTICLEReceived: March 22, 2017 Revised: September 8, 2017 Recommended by K.Zh. Seminsky Accepted: October 18, 2017For citation: Ruzhich V.V., Kocharyan G.G., 2017. On the structure and formation of earthquake sources in the faults located in the subsurface and deep levels of the crust.

Abstract:The paper briefly overviews the evolution of ideas concerning causes and mechanisms related to the origin of the Baikal rift zone (BRZ) in the centre of the Eurasian plate, discusses parameters of the recent seismogeodynamic impact on the seismotectonic regime in BRZ due to the Western Pacific subduction and the Indo-Eurasian collision, and attempts at estimating their contributions to the modern geodynamics of rifting processes in Pribaikalie. Seismic migration processes and specific density patterns of the released seismic energy are analyzed for two selected profiles between BRZ and the regions of collision and subduction. A statistical method is proposed to calculate seismic migration from space-time diagrams, and equations are developed to show a decrease in specific density of seismic energy released in the lithosphere at a distance from the interplate boundaries towards the Baikal rift. The modern geodynamic impact on the seismotectonic regime in BRZ due to the Indo-Eurasian collision is reflected in moderate horizontal compression of the lithosphere, mainly in the southwestern BRZ and partly in the central BRZ. In the transition area in this profile, the specific density of released seismic energy is about 1.72×1010 J/km 2 . The geodynamic impact on the seismotectonic regime in BRZ from the subduction zone (from the Nankai trough) is shown by a significantly lower specific density of released seismic energy, 1.02×1010 J/km 2 . In the lithosphere of the northeastern BRZ, a weaker geodynamic influence is mainly manifested by responses to strong seismic events and earthquake focal mechanisms with a clear strike-slip component in the Chara and Tokka basins located in the Aldan shield of the Siberian platform.We discuss a possible mechanism that drives the propagation of the geodynamic impact on BRZ from the interplate contact areas. In our opinion, the geodynamic influence propagates intermittently in the lithospheric plates due to motions of slow-deformation-wave fronts, which are reflected in the diagrams as seismic activity clusters. The longrange propagation of slow waves is realized through triggering of active faults in the lithosphere. Such faults interacting with slow wave deformations may be manifested as excited sources of dissipation of seismic oscillations resulting from a spontaneous release of the energy accumulated in the Earth interior. This mechanism of endogenous energy supply may explain the observed propagation of recordable slow elastoplastic deformations for many thousands of kilometres.Today, when the new materials are available to show more ancient ages of the early elements of BRZ, and it is established that the tectonic energy is reduced with distance from the interplate boundaries, there is no support for the hypothesis based on the role of the Indo-Eurasian collision in the formation of BRZ. A recordable seismotectonic impact on the seismic regime in BRZ can occasionally occur after a major seismic activity in the regions of collision and subduction. This phenomenon may b...

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