逆序断裂的发育特征与地震反射识别

在具有盆地基底和未固结盖层的双层结构的盆地里，由于松散盖层对基底断裂应变的吸收，晚期发育的基底断裂在进入盖层后，应变会逐渐减小甚至消失，形成下部错动大、上部错动小的特点，本文把这样的后期断裂称之为逆序断裂。当基底断裂为走滑断裂时，逆序断裂具有双层空间构造样式，即在盆地基底发育主干走滑断裂、而在盖层优先发育另外走向的次级雁行断裂。逆序断裂在渤海湾盆地普遍发育，本文以歧口凹陷的张北断裂带和白水头断裂带为例（这两处断裂带都在下构造层发育北东向基底走滑断裂、而在上构造层发育近东西向盖层次级正断裂），运用三维地震资料，结合沿层属性和垂直剖面，阐述了逆序断裂的发育特征和对地震反射剖面的识别。由于之前晚期的逆序断裂一般被当作早期同沉积生长断裂对待，本文希望能帮助重新认识渤海湾地区的区域断裂期次和构造发育演化过程。

Development characteristics and identification from the seismic reflection profiles of the reverse grading faults

Because of absorption of the basement fault strain by the loose cover，the late stage faults developed in the basin with the duplex of basement and unconsolidated cover，are characterized by intense deformation in the lower layers while weak deformation in the upper layers，which we call reverse grading faults in this paper. When the basement faults are strike slip faults，they would also have the spatial duplex feature，with main strike slip faults developed in the basement and secondary echelon faults in other trend in the cover deposition. These reverse strike slip faults have been widely distributed in the Bohai gulf basin. By 3 D seismic reflection data，this paper would take the Zhangbei and Baishuitou fault zones(both developed with NE main basement faults in lower layers and EW secondary cover faults in upper layers)as examples，to describes such development characteristics and identification features from the seismic reflection profiles of these reverse grading faults. As reverse grading faults used to be treated as contemporaneous growth faults，this paper would help to bring new interpretation of the regional fault structure and tectonic evolution.