论西安次级地裂缝

根据地震勘探结果，提出了西安地裂带由一条主地裂缝和一条规模较大的次级地裂缝组成。次缝位于主缝上盘，具有北倾北降的正断裂性质，并与主缝断裂呈“丫”字型构造，在深度300～500m处的第四系内与主缝汇合。在地表，次缝与主缝之间的距离多在50～120m，其间的地面呈陷落微地貌。地震勘探剖面上的次缝与主缝之间地层比较紊乱，似乎还有更小规模的裂缝构造，构成主缝到次缝间的断裂破碎带。对次缝的成因从区域构造应力场和自重应力场两方面给予了解释，并得到了以前的模拟试验结果和次缝出露地表情况的验证。据地面调查资料，凡次缝活动发育地段，其北侧主缝的活动相对较弱，甚至地表出露不明显。

On secondary ground fissure in Xi'an City

Based on the seismic exploration results, it is proposed that the Xi'an ground fissure belt is generally composed by one major fissure and one secondary fissure. The secondary fissure, located on the upfaulted block of the major fissure, has the normal fault property with north dip and north downthrown, and merges into the major fissure with Y-shaped distribution at depth 300-500m in Quaternary system. The secondary fissure lies on 50-120m south to the major fissure on the ground generally with the micro depression geomorphology. In view of the seismic sections, there are a few fissures between the major and secondary fissures and them compose a fracture zone. The development causes of the secondary fissure are interpreted from the regional tectonic stress filed and self-gravity stress filed, and they are verified by the previous simulation test and the real cases shown on the ground surface. According to the ground investigations, on the secondary fissure well-developed sections, its north major fissures are immature or in potential status.