断陷盆地正反转构造实验模拟及对茅东断裂带的启示

Experimental simulation of the positive inversion structure in rift basin and its enlightenment to Maodong fault zone

通过分析茅东断裂带地质构造和历史地震特征,结合离散元模拟实验,分析了挤压应力下断陷盆地构造反转及断裂活动特征,探讨了茅东断裂带作为断陷盆地在现今区域应力场作用下反转构造特性及正断层反转控震机制.结果表明:(1)挤压应力下,断陷盆地发生构造反转,促使盆地中先存正断层再活化以及浅部地层褶皱变形,但盆地中先存断层总体仍保持正断形态;(2)构造反转过程中,应力应变汇聚易优先发生在基底断层面上,并逐渐向沉积地层中传播,最终在浅表触发构造形变;(3)茅东断裂带属于活动断裂群,以茅东断裂等控盆边界断裂(基底断裂)活动为主,沿着该类断裂,应力应变汇聚明显,具备中、大地震的发震构造条件;断陷内其他隐伏的次级先存断裂也存在活动可能性,且断块间地层在压扭应力场下存在应力应变汇聚,同样具备浅源小震的发震构造条件.

Based on the regional geological structure and the features of historical earthquakes of Maodong fault zone, combining with the simulation experiment of discrete element method,the characteristics of positive inversing structures and fault activity in rift basin under compressive stress are analyzed and the mechanism of earthquake controlling of normal fault inversion are discussed in Maodong fault zone as a rift basin under the current regional stress field. Research results show that:(1) due to the regional compressive stress field,tectonic inversion occurs in the rift basin,which leads to the reactivation of the pre-existing normal faults in the basin or the folding deformation in the shallow strata,but the faults in the middle and deep strata still show normal faults on the whole;(2) under the regional compressional stress field,strain convergence tends to occur preferentially on the basement fault plane,and gradually propagates to sedimentary strata,resulting in structural deformation on the surface finally;(3) Maodong fault zone belongs to active faults group,where Maodong fault and other basin ? controlled boundary faults (basement faults) keep active mainly. Along these faults,stress and strain converge obviously in strata and have seismogenic tectonic conditions of moderate and large earthquakes;other hidden secondary pre -existing faults in the fault depression also have the possibility of activity,and there exists stress and strain convergence in interblock strata under transpression stress field. It possesses the seismogenic structural conditions of small earthquakes in shallow strata.