The Correlation Between The Fault Surface Morphology And Rupture Process

“Asperity”or “obstacle” on a fault surface in deep,which controls and affects the-rupture process,has been deduced from the pattern of co-seismic displacement on fault surface.Then,what is the “asperity” or “obstacle”? What geologic implication does it have? Is it a real geometric structure,or only different stress field on the fault? What is the relationship between the “asperity” or “obstacle” and the geometrical features of the rupture zone on surface? To resolve these problems and understand “asperity” or “obstacle” deeply,a further study on the relationship between morphologic characteristics of a fault surface and rupture process should be done.On a macro-scale,we analyze correlation between the geometrical features of co-seismic surface rupture and corresponding displacement.On a micro-scale,thourgh the experiment of stick sliding,we study the relationship between the topographic feature of the friction surface and the stress and strain field,micro-fracture distribution in unstable sliding process.We gain the following new findings:(1)The geometric characteristics of co-seismic surface ruptures and active faultsFault traces contain abundant information associated with fracture process and mechanics,so an accurate and quantitative description of their geometric characteristics is of great significance to perceiving fracture mechanism and fault evolution.We collected 52 co-seismic surface ruptures and 300 active fault traces to analyze their geometric characteristics by the method of power spectrum density.Our results showed that(1)the average power spectrum density has a distinct three-segmented characteristic in frequency domain,the power spectrum density characteristics represent the geometric characteristics of the boundary of tectonic block in the low frequency domain;it reflects the processes of lateral growth and linking together of several faults in the medium frequency domain;in the low frequency domain,below 100 meter scale on which the reflection point represents the effective resample length,the power spectrum density characteristics is meaningless;(2)in the middle and high frequency domains,the power spectrum density curves of coseismic surface rupture showed that there are obvious differences in roughness among three fault types,the reverse>the normal> the strike-slip,which implicate that the geometric characteristics of co-seismic surface rupture are controlled by the fault types;(3)compared with the co-seismic surface rupture,active fault appears much lower in power spectrum density,and this comparison result indicates the roughness of active fault trace becomes low with the increasing numbers of the faulting events and the lengths of active history,i.e.,the fault roughness decreases versus its maturity.(2)The correlation between geometric feature of co-seismic rupture and coseismic displacementResearch on correlation between geometric feature of co-seismic surface rupture and co-seismic displacement can effectively reflect the relationship between the seismicity distribution and the geometric morphology of sliding surface.In this paper,we compile the rupture traces and co-seismic displacements of 29 earthquake events.The features of surface rupture trace are characterized from three aspects,i.e.,change of slope,steps and roughness,and the correlation between these values and the co-seismic displacement is calculated.Through the correlation analysis between the surface rupture and co-seismic displacement,the following conclusions can be reached: 1)in comparison with the dip-slip earthquakes,the characteristics of surface rupture of strike-slip earthquakes have a higher correlation with the distribution of the co-seismic displacement,which indicates that the geometric features of strike-slip active faults are more valuable in the segmentation;2)in the group of strike-slip earthquake,based on the degree of correlation with the co-seismic displacement from high to low,the three geometric feature indicators of faultsare listed in order: Step Size>Strike Change>Roughness.(3)Fault surface data obtained by the topography measurement system and its precision analysisThe acquisition of high-precision tomographic features is of great significance for the study of the correlation between fault surface morphology and seismic nucleation,fracture propagation and termination.Due to the lack of reliable micron-scale tomographic measurement apparatus,it is not conductive for us to study the coherence of the fault surface morphology from large scale(unit: m-cm)to small scale(unit: ?m),as well as to study the relationship between the micro-morphology of the experimental frictional surface and the rupture process.In order to improve the measurement accuracy of the fault plane topography and overcome the shortcomings of the existing measurement methods,we have developed a topography measurement system with independent intellectual property rights.We measured the precision of the measurement system,and the results show that the precision of the plane positioning is better than 3.5?m;the vertical measurement precision is better than 4.5?m;the horizontal resolution can reach 0.62?m,vertical resolution 0.25?m.The topography measurement system has the following advantages:1)The measurement system can obtain the data even in a valley region with a large dip angle in the topography surface because of the beam emitted vertically by the laser sensor,so compared with other measurement means,it can avoid producing a blank area of measurements and get a complete area;2)the measurement system has a larger measurement range of 30cm×30cm.When the high-resolution measurement is performed on a large scale,the error caused by the registration of multiple measurement results can also be avoided.Using the topography measurement system,we scanned an experiment rock frictional plane and obtained high-resolution topography data.The roughness analysis results show that the topography measurement system can meet our surface analysis requirements on the micrometer scale.(4)The correlation between the roughness of frictional surface and rupture process on the stick-slip experimentOn the lab scale,we study the correlation between the geometric features of the fault frictional surface and the fracture process through stick-slip experiment.By sing the 2-Dimension geometric analysis method and the digital image correlation method,the collected digital photos of fault surface and displacement field of the fault surface were processed respectively.The following conclusions can be reached: 1)on the relative smooth fault plane,there is a negative correlation between the fault surface roughness and displacement distribution during the fracture process,the low value area of the fault surface roughness corresponds to the high value area of the parallel fault component of the displacement field.2)in the instability phase of the stick-slip event,the distribution of displacement field is related to the combination of the two fault plane roughness,that is,the overlap of low value regions of the two fault plane roughness correspond to the locked area(asperities)and the high value areas of the parallel fault component of the displacement field;3)the correlation between the roughness of the fault frictional surface and the displacement field distribution is consistent during several stick-slip events and does not change with the variation in loading conditions.