地震剖面中走滑断层旋向判断模型——以塔东阿拉干北断层为例

A Concept Model of Determination of Shear Sense of Strike-Slip Faults in Seismic Profiles:An Example from the Alaganbei Fault in the Eastern Tarim Basin

地震剖面解释中尚无走滑断层旋向的直接判别标志,本文提出了一个在地震剖面解释中直接判断走滑断层旋向的模型。该模型假定断层作用前既存的某个地层厚度有变化,则垂直或斜交地层厚度变化方向的走滑断层必定在穿过断层的地震剖面中两盘地层厚度不等。确定了地层厚度变化方向,又测定了剖面中两盘地层厚度,则走滑断层的旋向就可以唯一地确定下来。穿过塔里木盆地东部阿拉干北右行走滑断层的地震剖面资料证实了这一模型的适用性。

There is no indicator to directly determine the shearing sense of the strike-slip fault in seismic profiles until the model presented in this paper. We present a concept model to directly determine the shearing sense of strike-slip faults in seismic profiles. If the thickness of pre-existing certain strata is changing in some directions, the strata thicknesses in both walls of a strike-slip fault must be different in the seismic profiles across the fault. The shearing sense of the strike-slip fault would be uniquely determined while the thicknesses are measured and the strata thickness changing direction is figured out. On the assumption of that the thickness of certain strata is thinning in a direction and thickening in the opposite direction monotonously, the strata thicknesses of both walls of a fault, the strike of which parallel or oblique to the strata thickness changing direction, must be different. If the thicknesses of both fault walls are measured, the shearing sense of the fault would be uniquely determined. The fault wall with the thinner thickness of the certain strata must slip from the thinning direction of the strata. Therefore, the shearing sense of the fault would be determined certainly. For example, the strata of some Formations are thinning in north direction, while the strike-slip fault is NS trending, the thickness of the strata in eastern fault wall is thinner than that in western fault wall in the cross seismic profile section in E-W direction, and then the eastern thinner strata must come from north along the fault. Hence, the fault is a dextral strike slip fault. Reversely, if the strata are thicker in eastern fault wall, the fault would be a sinistral strike-slip fault. As an example, the explanation and strata thickness measurement data in the seismic profiles across the Alaganbei dextral strike-slip fault in the eastern Tarim basin indicates that the concept model is available.