Butterfly Failure Of Rock Mass And Mechanism Of Great Earthquake

The mechanism of earthquake occurrence is a hot issue and a major scientific problem that has been debated worldwide for hundreds of years.So far,the scientific community has not formed a seismomechanical model with clear physical significance.In the 21st Annual Meeting of China Association for science and technology,the"mechanism of great earthquake and its physical prediction method" together with the"exploration of new approaches to laser nuclear fusion" were listed as 20 cutting-edge scientific and engineering technical problems in 2019,which have a guiding role in scientific development and a key role in technological and industrial innovation.In 2016,the papers of Professor Ma Nanjie's team on the a mechanism of butterfly-mutation rockburst in coal seam roadway were published in the?Journal of China Coal Society?.Professor Qiao Jianyong proposed its association with the complex analytical dynamic system.He pointed out that when the petals of Leau-Fatou appeared,the system was sensitive to the initial value and gave a mathematical explanation of the basic ideas of the research results.Since then,after three years of cooperation with scientific research teams of both sides,this theoretical framework has been applied to the research on the mechanism of earthquake occurrence and other geosciences.Some scientific research results were formed as follows:"Conjugate shear fracture-seismic composite model based on structural stability of dynamic system","Mechanical mechanism and evolution of X-shaped conjugate shear fractures-seism"and "Sources of seismic energy based on butterfly failure theory".On the basis of the above three papers,this research further verified the calculation results of "Conjugate shear fracture-seismic composite model" by using numerical simulation and comprehensive analysis of the objective physical and mechanical phenomena accompanied by earthquakes.The following main conclusions and innovative results are obtained:(1)Further clarifying the mechanism of large earthquake caused by X-conjugate shear fractureWith the plate motion,Vertical,horizontal and shear high deviatoric stress fields are formed near the growing,consumed,and shear margins of plates.Under such stress regime,the surrounding rock of crust-elongated and soft-defective bodies(lower than the surrounding rock mass)will form the butterfly failure,which is the sign of X conjugate shear fracture.That is to say,the expansion of the butterfly failure will form exposed or hidden X-shaped conjugated fractures centered on soft and defective geological bodies.In addition,huge elastic energy is accumulated around the butterfly failures and is released every time when the butterfly wings extend.The released energy propagates outward as seismic waves to trigger earthquakes.The mechanical mechanism is as follows:if the failure zone in soft and defective rock mass appears as a butterfly or X shape in ultimate stress state,the butterfly-shaped failure zone shows rapid expansion due to a local tiny trigger stress;at the same time,a large quantity of elastic energy is released,thus inducing strenuous vibration of the crust.(2)Clarifying the relationship between the butterfly failure and the "seismic accompanyingness" of the earthquakeThe propagation of the butterfly rupture coincides with the release of seismic energy.The butterfly failure can induce the earthquake and the earthquake can also induce the generation and evolution of the X-shaped conjugate shear fracture.(3)Further quantitatively explaining burstiness of earthquakes,multi-earthquakes of strip,characteristics of concentrated energy release and multiple earthquakes of plate edge,by using the methods of theoretical formula calculation and computer numerical simulation"Burstiness of earthquakes" is a small-scale stress disturbance per unit time(10-3MPa/s),which causes the transient expansion of X-shaped conjugate shear fracture;"Multi-earthquakes of strip" is that each time the X-shaped conjugate shear fracture of the rock mass is accompanied by a certain amount of energy release and a certain magnitude of earthquake;"Concentrated energy release" is the formation of X-shaped conjugate shear fractures,which changes the surrounding rock mass stress environment and makes the fractured area concentrate a large amount of elastic energy.As long as the fractured area is expanded,the "internal energy" of the newly fractured and the "system energy" of elastic deformation of rock near the boundary of new fracture area will be released.The calculated range of seismic energy is included in the range of 0?1018J,which is consistent with current cognitive Richter scale 0-9 earthquake."Multiple earthquakes of plate edge" is that the butterfly failure of surrounding rocks of the defective body under the dominance of the high deviated stress field with different characteristics,leading to the earthquakes of different magnitudes.The magnitude of the butterfly failure-seim on the extinction edge is higher than that of the growth edge,and the earthquake is frequent,which can cause a large earthquake of magnitude 7 or more,in accordance with the existing rules.(4)Revealing the occurrence law of large earthquakes caused by X-shaped conjugated shear fractures resembling the life cycle of butterfliesCorresponding to the physical evolution period of X-shaped conjugated fractures,seismic activities resemble the life cycle of butterflies,that is,the occurrence of earthquakes is highly similar to the whole life cycle of butterflies.The weak,moderate,and strong earthquake stages during seismic activities coupling with the physical evolution of X-shaped conjugated fractures can be regarded as the egg,larvae,pupal,and eclosion stages of butterflies.Moreover,for any surrounding rocks of defective rock mass with mechanical properties according with the reality,there are always preparation and evolution laws of large earthquake caused by X-conjugate shear fracture resembling the life cycle of butterflies under effects of high deviatoric stress fields and different equivalent trigger stresses.(5)Clarifying the physical evolution process of X-shaped conjugate shear fractures.The evolution process of X-shaped conjugate shear fracture is from steady-state progressive to accelerated transition.During this process,the surrounding rock of the defect body changed from a circular,oval,and butterfly shape to an X-shaped failure morphology.The expansion of the fracture is sensitively dependent on the strength of the surrounding rock mass,and will exhibit non-X-shaped conjugate fracture characteristics such as "V","Y","/".(6)Summarizing the necessary occurrence conditions and prediction approaches for large earthquake caused by X-conjugate shear fracture in theory.The necessary conditions for large earthquake caused by X-conjugate shear fracture mainly include:presence of defective rock mass,appropriate strength of surrounding rocks(P1>Rc),presence of high deviatoric stress fields formed due to tectonics and plate motion(P1/P3>3),and the stress triggering earthquakes(?P1?0.001MPa/s).Once the above conditions are met simultaneously,butterfly-shaped fractures are bound to form abruptly and propagate in surrounding rocks of defective rock mass in the crust,accompanied with the occurrence of earthquakes of corresponding magnitudes.The mechanism of great earthquakes is high nonlinearity and extreme complexity.The research results of this paper are only based on the deduction of mathematical mechanics theory and an incompletely practical hypothetical test of numerical simulation,to understand and discuss the mechanism and physical evolution process of X conjugate fracture,which is a specific fracture mode and causes a large earthquake.We need to further carry out the application analysis and practical test of the theoretical research results.