Abstract: This paper studies the impact of the M_W9.0 Tohoku-Oki earthquake,March 11,2011,Japan on the crustal deformation,active fault movement and earthquake risk in northeastern China by using continuous GPS data. The result shows that the direction and amount of principal strain is different between coseismic and interseismic strain field. The Japan earthquake mainly affects the level of strain accumulation in northeastern China. The coseismic strain accumulation is equivalent to about 12.7-years long-term background strain accumulation. In other regions,the impact of coseismic strain on the background strain rate isn't obvious. Based on the coseismic strain and background strain rate,we select 4 major active faults for the analysis by using the relative movement time sequence of endpoints of GPS baselines which cross the Tanlu Fault,Zhangjiakou-Penglai Fault and Taihangshan piedmont fault,respectively. We find that the earthquake produced obvious left-lateral slip and extensional slip on the north segment of Tanlu Fault,and there is a tendency of slight continuous left-lateral movement and extension after the earthquake. But on the middle segment of Tanlu Fault,there is no obvious evidence of coseismic movement,but a slight increase of the right-lateral slip rate after the earthquake. As for Zhangjiakou-Penglai Fault located in North China,the fault was characterized by obvious right-lateral movement and extrusion in about one year after the earthquake, then resumed quickly to the original left-lateral movement and extension. This means that the fault's accumulated stress was released temporarily by the earthquake,then the regional stress resumed to its original level. The movement of Taihangshan piedmont fault isn't affected by this earthquake,therefore we infer that the earthquake affected areas did not spread to the Shanxi Rift System. In one word,the crustal strain accumulation and stress level of northeastern region in China is released by Tohoku-Oki earthquake,so we believe that the earthquake risk is reduced to a certain extent.

Key words: 3 ?11 Tohoku-Oki earthquake, crustal deformation, strain accumulation, earthquake risk analysis

摘要： 以中国东北部地区的GPS观测资料为基础,研究了2011年3月11日日本东部M_W9.0大地震对中国东北部地区的地壳形变场状态、活动构造的运动方式及地震危险性态势的影响。结果表明,该地震所引起的同震地壳应变场与研究区域长期地壳应变率场相对比,两者在主应变方向和大小等方面,整体上并无明显的一致性。该地震主要影响了中国东北区域应变积累水平,同震位移在瞬间所产生的应变,相当于该区域约12.7a的长期积累。而在东北以外的其他区域,同震应变对背景应变场的影响并不明显。基于同震应变以及背景应变场,选取了4个重要的活动断裂区段,利用一系列跨断裂连续GPS基线端点相对位置的时间变化序列进行分析,发现该地震使郯庐断裂北段发生了明显的左旋错动和拉张运动,且震后的变化趋势反映着轻微的继续左旋和拉张; 而对于郯庐断裂的中段,该地震并没有产生明显的错动和拉张,仅使其震后的右旋运动速率有轻微的加快; 对于华北地区的张家口-蓬莱断裂带,虽然在地震后约1a时期内表现为右旋挤压运动,但随后则快速回归到原有的左旋拉张运动,反映出这次地震的发生使该断裂的应力积累首先得到短暂的释放,随后区域应力又回归到原有水平; 太行山山前断裂带的运动态势未受这次地震的显著影响,因而推断出此次地震的影响范围并未波及到山西地堑系。总体而言,3 ·11日本大地震的发生,使中国东北部区域的地壳应变积累和应力水平有所缓解,因此,在某种程度上缓解了区域的地震危险性。

关键词: 3·11日本大地震, 地壳形变, 应变积累, 地震危险性分析