We extracted tectonic crustal deformation caused by the interplate coupling between the Pacific and North American plates from GNSS time series data at land-based stations in the Tohoku district, northeastern Japan, during the period from 21 March 1996 to 7 March 2011. Next, we estimated the spatiotemporal distributions of the slip deficit rates between the two plates prior to the 2011 Tohoku-oki earthquake for the 1997–2010 period by performing time-dependent inversion analysis. As a result, two strongly coupled regions were identified. One is located off the coast of Iwate Prefecture, whose reliability may not be high, where coseismic slip of the Tohoku-oki earthquake was small, indicating that this area may be a source region for a future megathrust earthquake. The other is a region with strong and continuous interplate coupling of more than 8 cm/yr from 1997 to 2010 in and around the epicenter of the Tohoku-oki earthquake. This area coincides with the area where coseismic slip greater than 20 m was estimated. Decrease of interplate coupling by approximately 0.4 cm/yr was identified at the downdip side of the region during the period from 2003 to 2008, reaching a coupling of 1.5 cm/yr in 2008, which would yield an increase in shear stress at its shallower strongly coupled region. We also identified that in 2010, the strongly coupled region rapidly expanded in southwestern and downdip directions. These results suggest that the shear stressing rate in the strongly coupled region might be accelerated, reaching rupture strength because of these two effects, thereby causing the main shock.

中文翻译：

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根据 GNSS 数据反演 2011 年东北冲地震前 14 年日本东北地区板间耦合时空分布

我们从1996年3月21日至2011年3月7日期间日本东北地区陆基站的GNSS时间序列数据中提取了太平洋板块与北美板块之间的板间耦合引起的构造地壳变形。通过进行瞬态反演分析，估计了 2011 年东北冲地震之前 1997 年至 2010 年期间两个板块之间滑移赤字率的时空分布。结果，确定了两个强耦合区域。一处位于岩手县近海，可信度可能不高，东北冲地震的同震滑移较小，表明该地区可能是未来特大逆冲地震的震源区。另一个是1997年至2010年东北冲地震震中及其周边地区，板间耦合强且连续，每年超过8厘米。该区域与估计同震滑移大于 20 m 的区域重合。 2003年至2008年期间，该区域下倾侧的板间耦合减少了大约0.4厘米/年，2008年耦合达到了1.5厘米/年，这将导致其较浅处的剪应力强烈增加耦合区域。我们还发现，2010年，强耦合区域向西南和下倾方向快速扩展。这些结果表明，由于这两种效应，强耦合区域的剪应力速率可能会加快，达到断裂强度，从而引起主震。