ON THE STRUCTURE AND FORMATION OF EARTHQUAKE SOURCES IN THE FAULTS LOCATED IN THE SUBSURFACE AND DEEP LEVELS OF THE CRUST. Part I. SUBSURFACE LEVEL

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 inMongoliain 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.