【摘要】 5.12汶川8.0级地震断层的同震位移方式、大小和空间变化为检验断层几何学、运动学与动力学分析理论与方法提供了一个现实范例。本文通过对汶川8.0级地震断层同震位移的几何学、运动学特征和可能的深部过程分析,并考虑到地震动力作用的影响,探讨了断层同震位移的地质意义和断层运动学模型问题,继而讨论了汶川8.0级地震过程中所呈现出的断层构造变形的现象对断裂构造分析的有关理论和方法的启示。提出了如下初步认识:(1)根据地震破裂面两侧地表高程差确定的断层垂直同震位移,并不完全是深部震源破裂的构造位移扩展到地表所致,而是包含了地震动力作用对断层破裂面两侧深部岩体的结构损伤破坏(膨胀)强烈程度差异所形成的非构造位移;(2)汶川地震的发震断层走滑-逆冲位移大小和方式的空间变化,可以用区域稳态构造应力和地震动力的联合作用给予合理解释,即断层的逆冲位移成分可以归因于为垂直断层的南东向的区域构造挤压应力作用之结果,而水平走滑位移则与震源体破坏过程形成的地震动力作用方向与不同区段断层的交角变化所致,即震源体上方映秀-北川断层南段和彭灌-江油断层,无论是区域构造应力,还是地震动力,都与断层走向近于直交,因此,断层以逆冲为主;而映秀-北川断层北段,即北川-青川段,由于地震动力方向与断层面斜交,并且越向北东方向交角越小,即使构造应力仍然为垂直断层走向,但构造应力和地震动力的联合作用,必然会导致走滑位移成分增加,自南向北位移的减小和震源体产生的地震动力作用的衰减;(3)汶川地震中发震断层同震位移,自南向北不仅位移方式呈现出由逆冲为主到逆冲走滑的变化,而且位移大小也逐渐减小,特别是在虹口一带,在同一摩擦镜面上先后出现了不同方向断层擦痕,即一次构造过程,就可在断层中先后形成不同方向运动学线理,反映了地震构造过程的运动学与动力学的复杂性。这些构造现象对历史断层运动学-动力学分析理论和原则提出了挑战。在研究断层历史活动方式和活动期次时,如何建立沿断层走向的运动学方式的变化与其相对应的区域构造应力场关系问题,利用断层不同方向的运动学线理确定的断层活动期次和活动方式的可靠性问题,断裂构造运动学-力学过程分析的理论和方法是否应该充分考虑地震动力作用的叠加影响问题等。这些有关地壳构造变形分析的基本科学问题值得构造地质学家进一步思考和探讨。更多还原

【Abstract】 The fault co-seismic displacement size,kinematics figuration and its spatial variation of Ms 8.0 Wenchuan earthquake fault also provide a practical example to test and check theory and methods of fault geometry,kinematics and dynamics analysis.With consideration of earthquake dynamic force,regional tectonic stress field and possible deep tectonic process,this paper discusses significances of fault co-seismic displacement in Wenchuan earthquake,its kinematic models,and implications of the tectonic deformation phenomenon for the theory and methods of fault structural anlysis.This study proposed the following preliminary achievements.Firstly,the co-seismic displacements determined by measuring the elevation contrast between two sides of the fault rupture surface is not entirely due to spreading of deep structural displacement,but maybe partly due to differences of the intensity of the structural damage(expansion)of deep rock masses between the upper and down fault blocks along fault rupture surfaces under the earthquake dynamic impact forces.The gravity,wave velocity and electrical resistivity changes before and after the earthquake may also be indicative of the deep rock of the existence of structural damage.Secondly,slip-thrust displacement and its spatial variation of seismogenic faults in Wenchuan earthquake could be interpreted by couple actions of regional tectonic stress and earthquakes dynamic impact forces,that is,the vertical displacement component can be attributed to south-east regional tectonic compression stress and earthquake dynamic impact forces that is nearly orthogonal to fault plane at the top of earthquake source body.This explanation could be supported by mainly taking thrusting in the south segment of Yingxiu-Beichuan fault and Pengguan-Jiangyou fault.While in the north eastern segment of Yingxiu-Beichuan fault,that is Wenchuan-Qingchuan segment,due to direction of earthquake dynamic impact forces not orthogonal to the fault plane,and the intersectional angle between them gradually decrease from south to north,even if the tectonic stress direction is still vertical to the fault,but the composite action of tectonic stress and earthquake dynamic force is bound to cause to the gradually increase of the strike-slip displacement component.The total displacement sizes of fault would be decrease with the increase of distance from the earthquake source body.Finally,the fault co-seismic displacement scale and its spatial variation,especially different direction scratches on the same fault friction mirror in Wenchuan earthquake,provide opportunity to reverse the theory and principles of the geometry and kinematics of the fault.When we carry out research on faults which underwent multiple deformation and activities,special attentions should be paid on how to identify different deformation episodes and their kinematics,and how to understand geometrical and kinematic changes along the fault and its relation to corresponding uniformly regional tectonic stress field uniformity.All these scientific questions related to crustral deformation are worth further investigation and thinking.更多还原