CNRS, Institut de physique du globe de Paris, Université Paris Cité, 75005, Paris, France.
CNRS, Géosciences Rennes, Université de Rennes, 35000, Rennes, France.
Sci Rep. 2023 Mar 8;13(1):3856. doi: 10.1038/s41598-023-30772-z.
Active faults accommodate tectonic plate motion through different slip modes, some stable and aseismic, others characterized by the occurrence of large earthquakes after long periods of inactivity. Although the slip mode estimation is of primary importance to improve seismic hazard assessment, this parameter inferred today from geodetic observations needs to be better constrained over many seismic cycles. From an analytical formulation developed for analyzing fault scarp formation and degradation in loosely consolidated material, we show that the final topographic shape generated by one earthquake rupture or by creep (i.e., continuous slip) deviates by as much as 10-20%, despite a similar cumulated slip and a constant diffusion coefficient. This result opens up the theoretical possibility of inverting, not only the cumulated slip or averaged slip rate, but also the number of earthquakes and their sizes from scarp morphologies. This approach is all the more relevant as the number of rupture events is limited. Estimating the fault slip history beyond a dozen earthquakes becomes very difficult as the effect of erosion on scarp morphology prevails. Our modeling also highlights the importance of trade-offs between fault slip history and diffusive processes. An identical topographic profile can be obtained either with a stable fault creep associated with rapid erosion, or a single earthquake rupture followed by slow erosion. These inferences, derived from the simplest possible diffusion model, are likely to be even more pronounced in nature.
活断层通过不同的滑动方式来适应板块运动，有些是稳定的且无震的，而另一些则以长时间不活动后发生大地震为特征。尽管滑动方式的估计对于提高地震危险性评估至关重要，但今天从大地测量观测推断的这个参数需要在多个地震周期内得到更好的约束。从用于分析松散固结材料中断层陡崖形成和退化的解析公式出发，我们表明，尽管累积滑移和扩散系数相同，但一次地震破裂或蠕动（即连续滑移）产生的最终地形形状会有 10-20%的偏差。该结果从理论上开辟了一种可能性，不仅可以反演累积滑移或平均滑移率，还可以根据陡崖形态反演地震数量及其大小。由于破裂事件的数量有限，这种方法更为相关。估计十几个地震以外的断层滑动历史变得非常困难，因为侵蚀对陡崖形态的影响占主导地位。我们的模型还强调了断层滑动历史和扩散过程之间权衡的重要性。具有快速侵蚀的稳定断层蠕动或单一地震破裂后缓慢侵蚀都可以获得相同的地形剖面。这些推断源自最简单的扩散模型，在自然界中可能更为明显。
