The Dynamics of Strike-Slip Step-Overs with Linking Dip-Slip Faults
The Dynamics of Strike-Slip Step-Overs with Linking Dip-Slip Faults
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DOI：
10.1785/0120050058
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发表时间：
2005-10
影响因子：
3
通讯作者：
D. Oglesby
中科院分区：
文献类型：
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作者：
D. Oglesby
断层阶跃与倾滑断层连接是世界范围内长走滑断层系统的常见特征。许多研究人员已经注意到，在某些情况下，地震可以跨越断层阶跃级联成大事件，而在其他情况下，破裂在阶跃处被阻止。也有证据表明，断层阶跃可能是地震成核的优先位置。本文采用三维有限元方法模拟了具有跨断层和连接倾滑断层的走滑断层系统的动力学。我发现，连接正断层或逆冲断层的存在大大增加了地震破裂穿过台阶传播的能力，从而导致更大的事件。此外，与连接正断层的扩张阶跃比与连接逆冲断层的压缩阶跃更容易发生贯通破裂。这种差异是由于走滑段上的滑动引起的倾滑断层上的正应力增量的符号：走滑段上的滑动导致扩张性台阶中的连接正断层上的负（松开）正应力增量，而挤压性台阶中的连接逆冲断层上发生相反的效果。即使在扩张性和压缩性台阶都可能经历贯穿性破裂的情况下，扩张性台阶通常也会经历更高的滑动，特别是在连接的正断层上。在挤压的情况下，破裂成核的连接逆冲断层可能会增加贯通破裂的可能性相比，成核的一个走滑段。在断层段之间的交叉点附近，断层段之间的应力相互作用也导致倾角的显著旋转远离从区域应力场推断的倾角。这一结果有助于强调在地震破裂过程中邻近断层段之间双向相互作用的重要性。这些结果也可能对沿沿着几何形状复杂的走滑断层系统发生大地震的可能性产生影响，并可能有助于解释为什么跨越有时作为障碍，有时作为大地震的成核位置。
Fault step-overs with linking dip-slip faults are common features on long strike-slip fault systems worldwide. It has been noted by various researchers that under some circumstances, earthquakes can jump across fault step-overs to cascade into large events, while under other circumstances rupture is arrested at step-overs. There is also evidence that fault step-overs may be preferential locations for earthquake nucleation. The present work uses the 3D finite element method to model the dynamics of strike-slip fault systems with step-overs and linking dip-slip faults. I find that the presence of a linking normal or thrust fault greatly increases the ability of earthquake rupture to propagate across the step-over, leading to a larger event. Additionally, dilational step-overs with linking normal faults are more prone to through-going rupture than compressional step-overs with linking thrust faults. This difference is due to the sign of the normal stress increment on the dip-slip fault caused by slip on the strike-slip segments: Slip on the strike-slip segments causes a negative (unclamping) normal stress increment on the linking normal fault in a dilational step-over, whereas the opposite effect occurs on the linking thrust fault in a compressional step-over. Even in cases for which both dilational and compressional step-overs can experience through-going rupture, dilational step-overs typically experience higher slip, particularly on the linking normal fault. In the compressional case, rupture nucleation on the linking thrust fault may increase the likelihood of through-going rupture compared to nucleation on one of the strike-slip segments. Near the intersections between the fault segments, the stress interaction between the fault segments also causes a significant rotation of rake away from that which would be inferred from the regional stress field. The results help to emphasize the importance of two-way interactions between nearby fault segments during the earthquake rupture process. The results also may have implications for the probability of large earthquakes along geometrically complex strike-slip fault systems, and may help explain why step-overs sometimes act as barriers and other times as nucleation locations for large earthquakes.