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，高达9.5级，发生在俯冲板块的边界。在这些边界上，当两个板块会聚时，一个板块潜入另一个板块之下，板块在接触处的摩擦可能导致非常大的地震，这些地震总共释放了全球地震能量预算的80%以上。这些所谓的大推力地震及其相关危害，包括海洋海啸，已造成数十万人死亡，如2004年在苏门答腊和2011年在日本。一个长期存在的问题是，为什么只有俯冲边界的某些部分有非常大的地震记录，而其他部分似乎没有能力举办大地震。地震发生时，弹性应力，积累在锁定的巨型逆冲断层的力量平衡在俯冲边界不断驱动收敛，突然释放时，摩擦断层强度超过了应力。人们一致认为，地震潜力的变化反映了大型逆冲断层弹性载荷的大规模差异。可变载荷被归因于俯冲参数，如板块收敛速度，上板块的强度，或板块之间的界面上的沉积物厚度。然而，地震重复时间通常比我们的仪器目录的持续时间长得多，因此，俯冲参数与最大地震规模的统计相关性仍然是不确定的。板块和界面属性之间的相互作用可能决定了应力的积累，因此需要一种物理模拟方法来了解不同因素如何影响巨型逆冲断层地震的可能性。通过规定几何形状和收敛速度，针对特定设置定制的粘弹性板块的局部尺度俯冲模型有助于了解地震周期的后果，包括决定海啸可能性的地表变形和断层滑动模式。这些模型不能提供俯冲参数如何控制应力载荷的大规模和长期差异的见解。其他更大规模的模型让板块的几何形状和运动动态发展，并有助于理解力的平衡和长期应力。然而，这些模型通常近似板作为粘性和忽略弹性应力。直到现在，建模能力才足够成熟，使粘弹性俯冲板块的大规模模型系统化成为可能。在我们团队的2D试点研究中，我们从模型中推导出了关系，这些模型让我们可以估计实际俯冲带的板块弯曲的弹性分量。我们发现，较高的弹性弯曲的估计与较高的观测到的相对数量的大地震（相比较小的事件）。这说明了这种大规模的粘弹性俯冲建模的承诺，了解megahutch地震potential.In这里提出的项目，我们将使用一个国家的最先进的板块建模平台（地下），这将使我们能够，第一次，运行一套系统的三维粘弹性俯冲模型，以模拟弹性能量存储在俯冲系统的变化。通过确定板块弯曲（下倾和沿走向）和上板块应力对俯冲板块、上板块和它们之间耦合强度的性质变化的响应，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规模之间的观测关系。从我们的模型中得出的关系将提供一种新的，基于物理学的方法来估计潜在的俯冲段周围的地球仪主机非常大的地震，包括在边界没有历史地震目录。