Giant earthquakes with magnitudes above 8.5 occur only in subduction zones. Despite the developments made in observing large subduction zone earthquakes with geophysical instruments, the factors controlling the maximum size of these earthquakes are still poorly understood. Previous studies have suggested the importance of slab shape, roughness of the plate interface contact, state of the strain in the upper plate, thickness of sediments filling the trenches, and subduction rate. Here, we present 2‐D cross‐scale numerical models of seismic cycles for subduction zones with various geometries, subduction channel friction configurations, and subduction rates. We found that low‐angle subduction and thick sediments in the subduction channel are the necessary conditions for generating giant earthquakes, while the subduction rate has a negligible effect. We suggest that these key parameters determine the maximum magnitude of a subduction earthquake by controlling the seismogenic zone width and smoothness of the subduction interface. This interpretation supports previous studies that are based upon observations and scaling laws. Our modeling results also suggest that low static friction in the sediment‐filled subduction channel results in neutral or moderate compressive deformation in the overriding plate for low‐angle subduction zones hosting giant earthquakes. These modeling results agree well with observations for the largest earthquakes. Based on our models we predict maximum magnitudes of subduction earthquakes worldwide, demonstrating the fit to magnitudes of all giant earthquakes of the 20th and 21st centuries and good agreement with the predictions based on statistical analyses of observations.

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什么控制着巨大的俯冲地震的最大震级？

8.5级以上的大地震仅发生在俯冲带。尽管在用地球物理仪器观测大俯冲带地震方面取得了进展，但对于控制这些地震最大规模的因素仍然知之甚少。先前的研究表明，平板形状，板界面接触的粗糙度，上板应变状态，填充沟槽的沉积物厚度和俯冲速率的重要性。在这里，我们提出了具有各种几何形状，俯冲通道摩擦构造和俯冲率的俯冲带地震周期的二维跨尺度数值模型。我们发现，低角度俯冲和俯冲通道中厚厚的沉积物是产生大地震的必要条件，而俯冲率的影响可以忽略不计。我们建议这些关键参数通过控制震源带的宽度和俯冲界面的光滑度来确定俯冲地震的最大震级。这种解释支持先前基于观察和定标定律的研究。我们的模拟结果还表明，对于发生大地震的低角度俯冲带，沉积物充填俯冲通道中的低静摩擦会导致上覆板中性或中等压缩变形。这些模拟结果与最大地震的观测结果非常吻合。根据我们的模型，我们预测了全世界俯冲地震的最大震级，