SUMMARY In order to generate plate tectonics, the near surface layer should not be too strong, but the causes for not-so-strong near surface layer remains unclear. We conduct mantle convection modelling in the spherical geometry to investigate the influence of the strength of the near surface layer. We explore a range of friction coefficients including the static high friction coefficient (∼0.6) as well as the reduced friction coefficients by fast fault motion in earthquakes. When the friction coefficient is low enough (<0.03), the surface layer is yielded by the convective stress, and the style of mantle convection appears the mobile-lid mode (plate tectonics style of convection). This style is relevant for the Earth where fault motion is unstable because of the low surface temperature. In contrast, for a high friction coefficient, the surface layer is too strong, generating the stagnant-lid mode. This case corresponds to Venus where fault motion is stable because of high surface temperature. Our calculations show that, in plate tectonic style of convection, the mantle convection is likely to be more vigorous, inducing the high convective stress that helps the operation of plate tectonics. In contrast, when stagnant-lid mode of convection appears, the convective vigor is likely to be low, inducing the low convective stress. Therefore, in each case, the interplay between the surface strength and convective stress tends to maintain the same mode of convection in a self-consistent way. We also investigate the relationship between mantle temperature and heat flux for two different modes of convection upon a change in friction coefficient. We found that the heat flow associated with mobile lid convection caused by low friction is less sensitive to the mantle temperature compared to a conventional mantle convection model, where the heat flow is highly sensitive to mantle temperature. This provides a possible mechanism to solve the thermal runaway paradox.

中文翻译：

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现实流变特性对地幔对流方式的影响：动摩擦的作用和流变特性的深度依赖性

小结 为产生板块构造，近地层不宜太强，但近地层不强的原因尚不清楚。我们在球面几何中进行地幔对流建模，以研究近地表层强度的影响。我们探索了一系列摩擦系数，包括静态高摩擦系数（~0.6）以及地震中快速断层运动降低的摩擦系数。当摩擦系数足够低（<0.03）时，地表层受对流应力的作用，地幔对流方式出现移动盖方式（板块构造方式的对流）。这种类型与由于地表温度低而断层运动不稳定的地球有关。相反，对于高摩擦系数，表层太强，产生停滞盖模式。这种情况对应于金星，由于表面温度高，断层运动是稳定的。我们的计算表明，在板块构造形式的对流中，地幔对流可能更加剧烈，产生有助于板块构造运行的高对流应力。相反，当对流出现滞盖模式时，对流活力可能较低，导致对流应力较低。因此，在每种情况下，表面强度和对流应力之间的相互作用倾向于以自洽的方式保持相同的对流模式。我们还研究了摩擦系数变化时两种不同对流模式的地幔温度和热通量之间的关系。我们发现，与热流对地幔温度高度敏感的传统地幔对流模型相比，由低摩擦引起的与移动盖对流相关的热流对地幔温度的敏感性较低。这为解决热失控悖论提供了一种可能的机制。