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逆冲走滑断裂中走滑分量大小的确定是判断断裂性质和应力场方向的重要参数,在野外主要依靠被断裂错开的标志线来判断。标志线的恰当选择,直接影响断裂走滑性质的判断及大小的测定。本文在对5.12汶川大地震同震破裂野外地质调查的基础上,详细分析了在同震逆冲断裂上所观察到的位移特征,指出当地表标志线与断裂斜交时,逆冲运动伴随的地表水平缩短将造成标志线产生沿断裂走向上的视走滑位移现象,并给出了基于不同地震陡坎模式的计算视走滑位移量的公式。根据视走滑位移计算公式,对实测走滑结果进行了计算、校正。校正结果显示彭灌(安县-灌县)断裂同震破裂带基本无走滑运动,为近纯逆冲性质;小鱼洞断裂和彭灌断裂上各自相隔数米的两个标志线分别出现左旋和右旋视走滑的例子进一步说明影响视位移误差的主要因素是水平缩短量,而非断裂走向的局部变化。本文的分析表明,野外测定逆冲走滑断裂的走滑位移时需尽量选择与断裂直交(垂直)的标志线,或注明标志线与断裂的夹角等几何关系;只有经视走滑位移校正后的测量才能代表断裂本身的真实走滑特征。
The determination of the size of strike-slip component in thrust strike-slip faults is an important parameter for judging the nature of faults and the direction of stress field, and mainly depends on the marked lines which are separated by faults in the field. The proper selection of the mark line will directly affect the judgment of the nature of the strike-slip and the determination of the size. Based on the field investigation of the coseismic rupture in the 5.12 Wenchuan earthquake, this paper analyzes in detail the observed displacement characteristics on the coseismic thrusts and points out that when the local surface marker line and the fault are skewed, the thrust movement is accompanied by The shortening of the surface level will cause the apparent strike-slip displacement along the strike of the marker line, and the formula for calculating the amount of apparent strike-slip displacement based on different seismic scarp modes is given. According to the calculation formula of the strike-slip displacement, the results of the measured slip are calculated and corrected. The calibration results show that there is almost no slip in the rupture coseismic rupture zone of Pengcai (Anxian-Guanxian), which is nearly purely purely thrusting. The two markers at Xiaoyudong-dong fault and Peng-irrigation fault at intervals of several meters show lev- And dextrorotatory slippage further illustrate the main factors that affect the visual displacement error is the amount of horizontal shortening, rather than the local changes in the fracture trend. The analysis of this paper shows that in the field, the strike-slip displacement of the thrusting strike-slip fault should be selected as much as possible when it is perpendicular to the fault (vertical) or the geometric relationship between the angle of the fault and the fault line. The corrected measurements represent the true strike-slip characteristics of the fracture itself.