关键词: 柴达木盆地, 南八仙背斜, 三维地震, 深、浅断裂耦合, 正演模拟

Abstract: Abundant basement deep faults and shallow faults are widely developed in the Qaidam Basin, but the genetic mechanism
between the coupling of the diverse faults is still controversial. In this paper, we analyze the geometry and coupling relationship of deep
and shallow fault systems across the Nanbaxian anticline in the northern margin of the Qaidam Basin, by using high-resolution 3D
seismic reflection data and drilling data. Results show that two EW-trending, high-angle basement faults are developed in the
Nanbaxian area, namely, the south-dipping Maxian fault and the north-dipping Xiannan fault. They were both initially formed in the
late Mesozoic and rejuvenated in the Cenozoic. Two sets of shallow normal fault systems are well developed within the Cenozoic in
Nanbaxian. One is NW-striking, and mainly en echelon distributed on the southern side (hanging wall) of the Maxian fault. The other is
EW-striking, and confined in the core of the Nanbaxian anticline above the Xiannan fault. This EW-striking fault cuts the NW-striking
normal fault system, and consists of a series of parallel sub-normal faults, forming a small graben structure within the Cenozoic above
the basement-involved Xiannan fault. We interpret that the NW-striking normal faults are related to extension at the western tail of the
Maxian fault caused by the sinistral strike slip, while the EW-striking normal faults result from local extension caused by thrust of the
high-angle Xiannan fault. Combined with previous research, we conclude that the widely distributed shallow fault systems are of various
origins with a complicated coupling with the deep fault systems in the Qaidam Basin, and that the pre-existing faults played an
important role in the Cenozoic deformation.

Key words: Qaidam Basin, Nanbaxian anticline, 3D seismic, coupling of deep and shallow fractures, forward modeling