We infer the postseismic deformation mechanisms following the 2011 Tohoku megathrust earthquake via an analysis of onshore geodetic observations. We focus on the temporal decay characteristics of postseismic deformation using continuous time-series data at time scales that span many orders of magnitude by means of high-rate GNSS data. Our analysis indicates Omori-like power-law decay of the horizontal ground displacement rates, with p-value (0.69) that is significantly smaller than that of the aftershock occurrence (~ 1). This slow decay implies a (non-Maxwellian) viscoelastic relaxation mechanism other than afterslip since immediately after the mainshock, which is inferred using only onshore geodetic data. Spatial distribution of the Omori parameters implies that the postseismic deformation will continue over 100 years in a down-dip area of the northern part of the mainshock fault. The decay characteristics of vertical displacement rates are also almost Omori-like, but data deviation from the fitting line several 100 days after the mainshock might reflect the change of the dominant mechanism of the postseismic deformation. This multi-time scale geodetic approach will provide important constraints for future viscoelastic models of Earth’s interior.

中文翻译：

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2011 年东北大地震后震后位移率的类似大森的缓慢衰减 (p < 1)

我们通过对陆上大地观测的分析来推断 2011 年东北大地震后的震后变形机制。我们通过高速 GNSS 数据在跨越多个数量级的时间尺度上使用连续时间序列数据来关注震后变形的时间衰减特征。我们的分析表明水平地面位移率的类似大森幂律衰减，p 值 (0.69) 明显小于余震发生 (~ 1)。这种缓慢衰减意味着除了后滑之外的（非麦克斯韦）粘弹性松弛机制，因为紧接在主震之后，这是仅使用陆上大地测量数据推断出来的。大森参数的空间分布表明，主震断层北部下倾区的震后变形将持续100多年。垂向位移速率的衰减特征也与大森相似，但主震后数百天数据与拟合线的偏差可能反映了震后变形主导机制的变化。这种多时间尺度的大地测量方法将为未来地球内部的粘弹性模型提供重要的约束。