Viscoelastic subduction modelling to understand megathrust earthquake potential

粘弹性俯冲模型以了解巨型逆冲地震的潜力

• 批准号: NE/Z000211/1
• 负责人: Saskia Goes
• 金额: $ 75.56万
• 依托单位: Imperial College London
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2024
• 资助国家: 英国
• 起止时间: 2024 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FZ000211%2F1
• 关键词: Viscoelastic; subduction; modelling; understand; megathrust

The largest earthquakes, of magnitudes up to 9.5, occur at subduction plate boundaries. At these boundaries, one plate dives below the other as the two plates converge, and the rubbing of the plates at their contact can lead to very large earthquakes, which together release over 80% of the global budget of earthquake energy. These so-called megathrust earthquakes and their associated hazards, including ocean-wide tsunamis, have caused 100s of thousands of deaths, as in Sumatra in 2004 and in Japan in 2011. A long-standing question is why only some parts of subduction boundaries have a record of very large earthquakes, while others do not appear capable of hosting major earthquakes. Earthquakes occur when elastic stresses, which accumulate at the locked megathrust as the balance of forces at the subduction boundary continuously drives convergence, are suddenly released when frictional fault strength is exceeded by the stress. It is agreed that variations in earthquake potential reflect large-scale differences in elastic loading of the megathrust. Variable loading has been attributed to subduction parameters such as plate convergence velocities, strength of the upper plate, or thickness of sediments on the interface between the plates. However, earthquake repeat times are generally much longer than the duration of our instrumental catalogues, and as a result, statistical correlations of subduction parameters with maximum earthquake size remain inconclusive. An interplay between plate and interface properties probably determines stress build up, and therefore a physical modelling approach is needed to understand how different factors contribute to megathrust earthquake potential.Local-scale subduction models of visco-elastic plates, tailored to a specific setting by prescribing geometry and convergence velocities, have helped to understand consequences of the earthquake cycle, including surface deformation and fault slip patterns that determine tsunami potential. Such models do not provide insight in how subduction parameters control large-scale and long-term differences in stress loading. Other, larger-scale, models let plate geometry and motions develop dynamically and have helped to understand the force balance and long-term stresses. However, these models usually approximate plates as viscous and neglect elastic stresses. Only now have modelling capabilities matured sufficiently to make running systematic sets of large-scale models of visco-elastic subducting plates feasible. In a 2D pilot study by our team, we derived relationships from models that let us estimate the elastic component of plate bending at actual subduction zones. We found that higher estimates of elastic bending correlated with higher observed relative numbers of large earthquakes (compared to smaller events). This illustrates the promise of such large-scale visco-elastic subduction modelling for understanding megathrust seismic potential.In the here-proposed project, we will use a state-of-the-art plate-modelling platform (Underworld) that will allow us to, for the first time, run a systematic set of 3D visco-elastic subduction models to characterise the variation of elastic energy storage in the subduction system. By determining the response of plate bending (downdip and along-strike) and upper-plate stress to variations in properties of the subducting plate, upper plate and coupling strength between them, we will test what combination of these properties can explain observed relations between subduction parameters and maximum earthquake size. The relations derived from our models will provide a novel, physics-based, method to estimate of the potential of subduction segments around the globe to host very large earthquakes, including at boundaries without a historic earthquake catalogue.

最大的地震幅度为9.5，发生在俯冲板边界。在这些边界上，随着两个板的汇聚，一个板块在另一个板上潜水，并且在其接触处摩擦板的摩擦会导致非常大的地震，这将释放超过地震能量全球预算的80％以上。这些所谓的超声层地震及其相关的危害，包括海洋范围的海啸，造成了100千人死亡，就像苏门答腊在2004年和2011年的日本一样。一个长期以来的问题是，一个长期以来的问题是，为什么只有俯冲边界的某些部分具有很大的地震，而另一些则没有能力托管大地震。当弹性应力在俯冲边界处的力平衡不断驱动融合时，地震发生在锁定的大型巨星处时，突然被释放出来。同意，地震电位的变化反映了大型弹性弹性的大规模差异。可变负载归因于俯冲参数，例如板收敛速度，上板的强度或板之间界面上沉积物的厚度。但是，地震重复时间通常比我们仪器目录的持续时间长得多，因此，俯冲参数的统计相关性具有最大地震尺寸的俯冲参数。板块和界面性能之间的相互作用可能决定了压力的增加，因此需要一种物理建模的方法来了解不同的因素如何有助于大型地震潜力。临时尺度俯冲粘贴模型，该模型量身定制，用于通过规定了地面构造的范围的范围，该模型通过规定了范围的范围，以确定范围的范围，并将其构成地球范围的造成范围，并构成了地面的影响。这样的模型没有提供有关俯冲参数如何控制应力载荷的大规模和长期差异的见解。其他大规模的模型使板的几何形状和动作动态发展，并有助于理解力平衡和长期应力。但是，这些模型通常将板近似为粘性和忽略弹性应力。直到现在，建模功能就足够成熟，以使粘弹性俯冲板的大规模模型运行。在我们的团队的2D试点研究中，我们从模型中得出了关系，这些模型使我们估计了实际俯冲带在实际俯冲区域的弹性组件。我们发现，较高的弹性弯曲估计值与观察到的相对数量较大的大地震数（与较小的事件相比）相关。这说明了这种大尺度粘膜弹性俯冲建模的希望，以理解大型地震潜力。在此处所提供的项目中，我们将使用最先进的板块模型平台（地下世界），这将使我们首次运行3D Visco弹性俯冲模型的系统，以表征巨大的量化系统，以表征弹性的量化模型。通过确定板弯曲（倾斜和沿形状）和上板应力对俯冲板，上板和它们之间的耦合强度的变化的响应，我们将测试这些性质的组合可以解释俯冲参数和最大地震大小之间观察到的关系。从我们的模型中得出的关系将提供一种基于物理的新方法，以估算全球俯冲段的潜力，即在没有历史悠久的地震目录的边界上进行非常大的地震。