Study of prestack elastic parameter consistency inversion methods

The three parameters of P-wave velocity, S-wave velocity, and density have remarkable differences in conventional prestack inversion accuracy, so study of the consistency inversion of the ＂three parameters＂ is very important. In this paper, we present a new inversion algorithm and approach based on the in-depth analysis of the causes in their accuracy differences. With this new method, the inversion accuracy of the three parameters is improved synchronously by reasonable approximations and mutual constraint among the parameters. Theoretical model calculations and actual data applications with this method indicate that the three elastic parameters all have high inversion accuracy and maintain consistency, which also coincides with the theoretical model and actual data. This method has good application prospects.

Three-dimensional high-resolution velocity structure imaging and seismicity study of Yangbi Ms6.4 earthquake

In this study,based on the body wave arrival data of 5506 earthquakes recorded by 32 fi xed stations and 94 temporary stations in Yangbi and surrounding areas,the source parameters of Yangbi Ms6.4 earthquake sequence and three-dimensional(3-D)fi ne Vp,Vs,and Vp/Vs were inverted by using the consistency-constrained double-diff erence tomography method.The results showed that the focal depth after relocation was mostly in the range of 3–10 km,evidently nearly horizontally distributed,and concentrated in the weak area of the high-velocity body or at the side of the high-low-velocity body transition zone toward the high-velocity body,showing a good corresponding relationship with the velocity structure.The velocity structure in the Yangbi area has remarkably uneven characteristics.The seismic activity area is dominated by high-velocity bodies prone to brittle fracture near the surface.As the depth increases,low-velocity anomalies appear.A signifi cant diff erence was observed in the wave velocity ratio between the upper and lower sides of the seismically dense strip.Based on the focal mechanism of the Yangbi Ms6.4 earthquake and the fine 3-D velocity structure,this article concludes that the Yangbi Ms6.4 earthquake was caused by a strong regional tectonic stress concentrated in the relatively weak area by hard high-velocity bodies on the northwest sides.The Ms5.6 foreshock broke the inherent balance of regional stress and promoted the occurrence of the Yangbi Ms6.4 mainshock.Afterward,the stress was adjusted to a new equilibrium state through a large number of aftershocks,forming a foreshock–mainshock–aftershock type of seismic activity model.Based on the activity law of the Yangbi Ms6.4 earthquake sequence and characteristics of the 3D velocity structure distribution,this paper speculates that the seismogenic structure of the Yangbi earthquake was possibly a northwest strike-slip buried fault with a depth of 3–10 km on the southwest side of the Weixi–Qiaohou fault.

沥青路面结构层模量反演最佳特征点的确定

基于落锤式弯沉仪(falling weight deflectometer,FWD)检测数据的路面结构层反演模量逐渐成为评价路面结构承载力的重要指标.在结构层模量反演方法中,弯沉盆规律法能够得到反演唯一解,工程应用性强.但现阶段弯沉盆规律法中,用于反演路面基层模量、面层模量的特征点位置的确定均基于理论分析,未得到实测弯沉盆数据的验证.因此,为进一步确定特征点的最佳位置,我们对不同路面结构不同层位的弯沉盆实测数据进行了研究.首先,利用交通运输部RIOHTRACK足尺环道试验的弯沉数据,分析了不同特征点位置对基层反演模量的影响;其次,以基于不同层位弯沉数据反演出的基层模量是否具有一致性为原则,确定了特征点的最佳位置;最后,利用独立弯沉数据对其准确性进行了验证.结果表明,对于实测弯沉盆数据,特征点选取位置对逐层反演基层模量一致性具有显著影响;对于2层结构体系,特征点位置选取为距离荷载中心点30 cm处,对于3层结构体系,特征点位置选取为荷载中心点和距离荷载中心点60 cm处时,逐层反演的基层模量一致性最好.