Experimental Study On The Influence Of Normal Stress Distribution On Seismic Nucleation Position

Before the earthquake,will slide in a part of the fault,the so-called earthquake nucleation.Fault contact homogeneity is common in the field,and the fault stress distribution caused by it is an important factor affecting earthquake nucleation and rupture.The initial location and extension characteristics of the nucleation zone are controlled by the fault stress distribution,however,previous studies focused on a uniform normal stress distribution.In fact,the normal stress distribution on the fault surface is affected by the inhomogeneity of multiple scales in the field fault geometry.Studying the inhomogeneity of normal stress distribution is important for the analysis of possible seismic nucleation locations in the field.In this experimental study,different normal stress distribution was realized to achieve the influence of inuniformity of normal stress distribution.The experiment of uniform and heterogeneous contact mode is carried out,in which the spatial and temporal evolution process of fault viscosity-slip instability is observed by means of strain,displacement,acoustic emission and load.The following understanding has been obtained:(1)Nucleation begins in the weak contact zone.Uniform contact fault,the normal stress distribution at both ends of the high middle low shape,nucleation is located in the middle of the low normal stress zone,dynamic rupture from the nucleation zone to both ends of the fault,where the speed of the non-loading end expansion is large;The heterogeneous contact fault,the normal stress distribution is high at both ends and in the middle,and the nucleation is located in the weak contact zone near the loading end.(2)In a sticky slip time period,for uniform contact,the acoustic emission is mainly concentrated on the sample loading end;for inhomogeneous contact small sticky slip event stabilization phase acoustic emission concentrated in the weak contact zone.Near the sticky slip event,the Aemission frequency begins to increase,and the magnitude is mostly distributed in-7～-8;(3)Using the Brune model,the stress drop of small events was obtained by the acoustic emission elastic waves.For the uniform contact fault,the small event stress drop is mostly less than 2.0 MPa,and the average value is about 1.663MPa;for heterogeneous contact faults,the small event stress drop is less than 0.2 MPa,with the mean value of about 0.139 MPa.In general,the small event stress drop of heterogeneous contact is much weaker(about one order)than the uniform contact fault;(4)Whether uniform or non-uniform contact,the nucleobservation of the main sticky slip event shows different expansion speeds on both sides;In contrast,there are two or more turn frequencies in the AE spectrum of sticky slip events during this process.