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大部分强震都发生在海沟,那里是海洋板块向大陆板块俯冲的地方。大量矩震级MW9.0以上的地震发生在若干区域,包括智利,阿拉斯加,堪察加半岛和苏门答腊岛等。位于太平洋板块俯冲鄂霍茨克板块的日本海沟,历史记载上没有发生过MW9.0地震,除了至今震级还有争议的公元869年Jogan大地震[1](可能超过MW9.0)。然而,根据最新的大地测量资料估算的应变积累速率比已发生的板块间地震的平均释放速率要高[2~6]。这一发现又引发了这样的疑问:这些区域如何释放积累的应变。2011年3月11日发生的逆冲型MW9.0强震(下文中均称为日本东北大地震),撕裂了日本东北部的太平洋海岸板块边界。我们报道根据GPS网络监测到的地表位移确定的同震与震后滑动特征。同震滑移区域沿日本海沟方向长约400 km,与震前闭锁区域基本吻合[4]。震后滑动不仅覆盖了同震滑移区域,而且扩展到了其邻区,甚至其影响已经达到100 km深度区域,引起2011年3月25日的MW8.3地震。由于东北地震释放了积累数百年的应变,之前提到的应变积累与释放不平衡的问题可能得到部分解释。这次东北地震同时也提醒我们,即使在过去没有发生过强震的其它海沟地区,也有发生MW9.0强震的潜在危险。因此,利用空间对地形变观测技术监测应变积累,以确定强震潜在危险区是非常重要的。
Most of the strong earthquakes occurred in the trench, where the ocean plate subducted the continental plate. A large number of earthquakes with MWOM magnitude of 9.0 occurred in several regions, including Chile, Alaska, Kamchatka Peninsula and Sumatra Island. There are no historical reports of MW 9.0 earthquakes in the Japan trench subducting the Okhotsk plate from the Pacific plate, except for the magnitude 86 Jogan earthquake that has hitherto been devastating (1) (possibly exceeding MW9.0). However, the rate of strain accumulation estimated from the latest geodetic data is higher than the average rate of release of earthquakes that have occurred [2-6]. This discovery raises the question again: how these regions release the accumulated strain. The thrust-type MW 9.0 strong earthquake (hereinafter referred to as the “Great Northeastern Japan Earthquake”) on March 11, 2011, torn the Pacific coast plate boundaries in northeastern Japan. We report the coseismic and post-earthquake slip characteristics determined from the surface displacements monitored by the GPS network. The co-seismic slip region is about 400 km long along the Japan Trench, which is consistent with the pre-earthquake blocking area [4]. The post-earthquake slippage not only covers the co-seismic slip region but also extends to its neighboring region. Even its impact has reached a depth of 100 km, causing the MW8.3 earthquake on March 25, 2011. Due to the release of accumulated strains of hundreds of years in the NE earthquake, the previously mentioned problem of imbalance in strain accumulation and release may be partially explained. This earthquake in Northeast China also reminds us that there is a potential danger of occurrence of the M9.09 earthquake even in other trench areas where no strong earthquakes occurred in the past. Therefore, it is very important to use the space-to-ground deformation observation technology to monitor the strain accumulation in order to determine the potential danger zone of strong earthquakes.