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首页> 外文期刊>Journal of geodynamics >On the effect of a low viscosity asthenosphere on the temporal change of the geoid—A challenge for future gravity missions
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On the effect of a low viscosity asthenosphere on the temporal change of the geoid—A challenge for future gravity missions

机译：低粘度软流圈对大地水准面时间变化的影响-未来重力任务的挑战

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New satellite technology to measure changes in the Earth's gravity field gives new possibilities to detect layers of low viscosity inside the Earth. We used density models for the Earth mantle based on slab history as well as on tomography and fitted the viscosity by comparison of predicted gravity to the new CHAMP gravity model. We first confirm that the fit to the observed geoid is insensitive to the presence of a low viscosity anomaly in the upper mantle as long as the layer is thin (～200 km) and the viscosity reduction is less than two orders of magnitude. Then we investigated the temporal change in geoid by comparing two stages of slablet sinking based on subduction history or by advection of tomography derived densities and compared the spectra of the geoid change for cases with and without a low viscosity layer, but about equal fit to the observed geoid. The presence of a low viscosity layer causes relaxation at smaller wavelength and thus leads to a spectrum with relatively stronger power in higher modes and a peak around degrees 5 and 6. Comparing the spectra to the expected degree resolution for GRACE data for a 5 years mission duration shows a weak possibility to detect changes in the Earth's gravity field due to large scale mantle circulation, provided that other causes of geoid changes can be taken into account with sufficient accuracy. A discrimination between the two viscosity cases, however, demands a new generation of gravity field observing satellites.
机译：测量地球重力场变化的新卫星技术为探测地球内部低粘度层提供了新的可能性。我们根据板块的历史以及层析成像法使用了地幔密度模型，并通过将预测重力与新的CHAMP重力模型进行比较来拟合粘度。我们首先确认，只要地层较薄（〜200 km）且粘度降低幅度小于两个数量级，对观测大地水准面的拟合对上地幔中低粘度异常的存在不敏感。然后，我们根据俯冲历史或通过层析成像得出的密度平流比较板状沉陷的两个阶段，研究了大地水准面的时间变化，并比较了有和没有低粘度层但与水面大致相等的情况下大地水准面变化的光谱。大地水准面低粘度层的存在会导致在较小波长处的弛豫，从而导致光谱在较高模式下具有相对较强的功率，并在5度和6度附近出现峰。将光谱与GRACE数据预期的度分辨率进行比较，历时5年如果可以充分考虑到大地水准面变化的其他原因，那么持续时间表明探测到由于大规模地幔环流引起的地球重力场变化的可能性很小。然而，要区分这两种粘度情况，就需要新一代的重力场观测卫星。

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