Numerical Simulation Of Radiated Seismic Wave Field Caused By Seismicrupture Source

Slope failure caused by earthquake is a common earthquake disaster. The basic reason for the formation of earthquake disaster is the seismic dynamic effect. The study of the focal mechanism of seismic rupture sourceis helpful to understand the process of the seismic wave radiation and mode of earthquake action applied to engineering site.Based on fully understanding of the double-couple source whose mechanical effect is equivalent to the fault movement and referring to regional seismic geological condition and seismic activity in Tianshui area,the regional crustal model and fault source model were built, and FLAC3 Dwasused to numerically simulate radiated seismic wave field caused by different fault in order to provide a scientific basis for the study mode and intensity of earthquake. Based on the simulation results analysis of the radiatedseismic wave field created by rupture sources of normal fault,reverse fault and vertical strike-slip fault,the following conclusions are summed up:(1) Radiatedseismic displacement field of rupture source has an apparent feature of double-couple source. The field is a quadrantaldistribution on the normal plane which goes through the geometric center of the fault.Radiatedseismicfield has rupture directivity effect.The amplification effectof vibration amplitudeof rupture is found obviously in the positive direction of rupture.(2) For normal fault, reverse fault and the vertical strike-slip fault, amplitude of displacement velocity and acceleration on the normal plane which goes through the geometric center of fault has a larger component on the direction of rupture rather than on its perpendicular direction.(3) Simulation results show that the hanging walleffect of the reverse fault is stronger than that of normal fault. For reverse fault, its positive direction of rupture points to the ground surface. The seismic response on ground surface for reverse fault is intense for the effect of hanging wall effect and rupture direction effect. On the contrary, the rupture direction of normal fault points to the reverse direction,which causes the rupture directivity effectnot obvious.When dip angle is close to 90 degrees, hanging wall effect disappears and rupture direction effect is outstanding.(4) For normal and reverse faults,when fault dip is small,with increasing distance from the epicenter, the ground response values within a certain range of the ground surface from the epicenter show a unilateral decrease trend along the inclination direction of the fault. With the increase of the dip angle of fault,peak seismic dynamic response values of the ground surface within a certain distance from the epicenterbecome closer to the epicenter.(5) For a vertical strike-slip fault,seismic response component on the rupture direction in the middle part of the horizontal profilewhich is close to the groundis smaller than its two sides. When the horizontal profile is a certain distance from the ground and close to the fault, seismic response component on the rupture direction in the middle part of the horizontal profilewhich is close to the groundis larger than its two sides.(6) Simulation results show that focal stress field created by rupture source coincide with corresponding theoreticalfocal stress fieldgiven by double-couple source, and radiatedseismic displacement field of rupture source has an apparent characteristic of double-couple source,which reflects the rationality of simulating rupture source in this paper. It also contributes tounderstand the seismic intense distribution, to find rupture direction and dip direction of the fault based on seismic monitoring data and the phenomenon of symmetrically distributed intensity regions, and to provide basis for the study of seismic dynamic action mode and intensity suffered by slopes.