Major Tsunami Risks from Splay Faulting
Major Tsunami Risks from Splay Faulting
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扇状断层造成的主要海啸风险
DOI：
10.5772/13375
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发表时间：
2011
影响因子：
--
通讯作者：
M. Heidarzadeh
中科院分区：
文献类型：
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作者：
M. Heidarzadeh
从2004年苏门答腊-安达曼大地震中得到的主要教训之一是，大型俯冲地震引起的海啸产生过程相当复杂。因此，通过假设大型逆冲断层的简单破裂来模拟海啸，可能无法解释近场观测到的海啸上升的实际变化。从这个角度来看，2004年印度洋海啸是海啸研究的一个里程碑，它清楚地显示了次级海啸源对近场海啸高度的强化作用。由主俯冲地震引发并在局部造成海啸的现象，除了在俯冲带上的主滑动外，被称为次级海啸源。最重要的次级来源是海底滑坡，其影响主要体现在1992年的弗洛雷斯岛海啸（Synolakis and Okal, 2005; Hidayat et al., 1995），以及在一些大型俯冲地震中观察到的展断层分支，如1946年的南开海啸（Cummins and Kaneda, 2000）， 1960年的智利和1964年的阿拉斯加海啸（Plafker, 1972），以及最近的2004年苏门答拉-安达曼地震和海啸（Sibuet et al., 2007）。在这里，在本章中，我们将重点讨论展断层，它被认为是重要的次级海啸源之一，并且在过去的海啸中造成了很大一部分海啸死亡。展断层，有时被称为叠瓦状断层，是从俯冲带向上分支到海底的陡倾逆冲断层。由于展断层往往具有陡峭的倾角，它们能够产生较大的海底变形，从而显著增加近场海啸的上升高度。图1图解地显示了一个从板块边界分支出来的展断层。如图所示，在展向断层的位置，海底隆升会突然增加。很明显，这种增强的海底隆起将在近场引起更大的海啸波高。在此背景下，如果不考虑大俯冲带地震可能引起的展向断层分支的影响，海啸危险性评估可能会低估实际存在的海啸危险性。因此，在本章中，我们研究了展向断层对近场海啸波的影响。首先，回顾了一些实际的展向断裂案例。在此基础上，讨论了从主板块边界出发的展斜断层分支的特征。在下一节中，将对海啸进行数值模拟，以研究近场斜断层对海啸波高的影响。最后，我们做了一些实际的
One of the main lessons learned from the great 2004 Sumatra-Andaman earthquake was the fact that tsunami generation process due to large subduction earthquakes is rather complicated. Hence, modelling tsunamis by assuming a simple rupture on a megathrust may not account for actual variations of observed tsunami runups in the near field. From this viewpoint, the 2004 Indian Ocean tsunami was a milestone in tsunami research in that it clearly showed the effect of secondary tsunami sources on intensifying the near-field tsunami heights. The phenomena that are triggered by the main subduction earthquakes and locally contribute to tsunami in addition to the main slip on the subduction zone are known as secondary tsunami sources. The most important secondary sources are submarine landslides, whose effect was mainly evidenced during the 1992 Flores Island tsunami (Synolakis and Okal, 2005; Hidayat et al., 1995), and splay fault branching which was observed during some large subduction earthquakes such as the 1946 Nankai tsunami (Cummins and Kaneda, 2000), 1960 Chilean and 1964 Alaskan tsunamis (Plafker, 1972), and most recently during the 2004 Sumatra-Andaman earthquake and tsunami (Sibuet et al., 2007). Here, in this chapter we focus on splay faults which are known as one of the important secondary tsunami sources and were responsible for a large part of tsunami deaths during past tsunamis. Splay faults, sometimes known as imbricate faults, are steeply-dipping thrust faults which branch upward from the subduction zone to the seafloor. As splay faults often have steep dip angles, they are capable of producing large seafloor deformation which can significantly increase tsunami runup heights in the near-field. Figure 1 schematically shows a splay fault which branches from the plate boundary. As shown, an abrupt increase in seafloor uplift happens at the location of the splay fault. It is clear that this enhanced seafloor uplift will cause larger tsunami wave heights in the near field. With this background, it is clear that tsunami hazard assessment without taking into account the effect of possible splay fault branching due to large subduction zone earthquakes may result in underestimating the actual existing tsunami hazards. Hence, in this chapter we study the consequences of splay faulting on tsunami waves in the near-field. First, we make a review of some actual splay faulting cases. Then, the characteristics of splay fault branching from the main plate boundary will be discussed. In the next section, numerical modeling of tsunami will be performed to investigate the effect of splay faulting on tsunami wave heights in the near-field. Finally, we make some practical