Experimental Study On AE Characteristics In The Process Of Fault Stick-slip

Earthquakes are a common destructive natural phenomenon.The mechanism of shallow earthquakes is stick-slip during sliding along old or newly formed faults.Stick-slip is a process in which the two sides of the fault are locked and the stress and strain accumulate until the sudden release,resulting in relative displacement dislocation.A large amount of energy is released in the process of instability dislocation.It is of great significance to study the mechanism of stick-slip dislocation and the extension process of fault stick-slip instability for earthquake prediction.In this paper,the prefabricated coarse grain is long granite slide friction fault model experiment,the different angle,different loading rates and lateral pressure under the mechanics features and acoustic emission parameters in the process of fault stick-slip,frequency,fractal dimension and other characteristics,analysis and summary of rock friction sliding instability mechanism and characteristics of acoustic emission evolution rule,early warning and to provide reference for earthquake prediction.By analyzing the mechanical characteristics of the stick-slip process under different loading conditions,it can be found that the stick-slip characteristics of the fault are different under different loading conditions.The change of lateral pressure and dip angle will change the stress state of fault plane and affect the contact state of concave-convex body,which is macroscopically manifested as the change of friction strength of fault plane.When the loading rate decreases,there is a relatively long time for adjustment and physical healing between the interrupted planes in the loading process,and the stress state of the broken planes changes.The AE characteristics of different stages of faults were studied by using the AE system experiment method.It was found that the number of AE events increased steadily in the stress accumulation stage,and the event energy levels were relatively small.The FFT transform of typical AE events shows that the signal amplitude is small and the frequency is high.By calculating b value and fractal dimension D,it can be seen that the distribution of micro-fracture scale remains stable,and the micro-fracture scale is mainly small.When fault instability and dislocation occurs,AE events increase suddenly,and high-energy events appear periodically with stick-slip events.The AE event frequency is low and the amplitude is large,but the signal is few,which corresponds to the generation of large-scale micro-fracture.When approaching instability,b value suddenly drops,and fractal dimension D drops to the lowest value,indicating that stick-slip events occur with an increase in the proportion of large-scale micro-fractures,which turn into shear fractures.At this stage,large-scale micro-fractures increase and eventually destabilize.By comparing the AE characteristics under different loading conditions,it can be concluded that when the inclination angle changes from 34° to 45°,the stress state changes and stick-slip is not easy to occur.The AE energy increases during stick-slip instability,and the proportion of large-scale micro-fracture before and after stick-slip instability is larger.By comparing the AE characteristics under different lateral pressures,it can be found that,with the increase of lateral pressures,the growth rate of AE count increases,the slip of fault plane intensifies,and the change degree of fracture scale is small,but the proportion of large-scale micro-fracture increases in stick-slip.When the loading rate changes,the distribution of AE events in each frequency band is similar at 1μm/s and 5μm/s.When the loading rate is 10μm/s,the stress drop and dislocation displacement are relatively small.However,from the perspective of the AE dominant frequency,the fault plane slip is more severe.As for the precursor information of faults,the occurrence of high-energy AE events can be used to predict the stick-slip of faults.Fractal dimension D and b values are also two important indexes for evaluating rock instability failure.The variation trend of fractal dimension D and b value is consistent,and b value has a sudden drop before the occurrence of stick-slip,which can be used as a prediction index.HHT is used to analyze the AE signals of instability events.It is found that Hibert spectrum changes earlier than signal waveform,which can be used as the precursor feature of stick-slip instability of faults.There are 49 figures,9 tables and 113 references in this paper.