The 2008 Wenchuan earthquake occurred on the eastern boundary of the Bayan Har block. To understand better the regional dynamic environment and its relation to the earthquake, this research studies the kinematics and deformation of the fault systems of the northern and eastern boundaries of the block, as well as the correlation of occurrences of major earthquake sequences on the two boundaries, based on analyzing data from active tectonics, focal mechanism, GPS station velocity, earthquake rupture distribution and seismicity of historical major earthquakes. The result shows that, owing to the resistance of the South China block, the east- to southeast ward “extruding” movement of the Bayan Har block, which is manifested by the active left-lateral strike-slip faulting along the northern boundary of the block, is transformed into thrust faulting and lateral shortening with strike-slip faulting on the eastern boundary of the block. This suggests that the “extruding” movement of the block has been “loading on” the eastern boundary remarkably. Such loading is also presented in the correlation of occurrences of major earthquake sequences on the two fault systems of the northern and eastern boundaries of the block. From the middle to late 19th century to 2001, a sequence of 8 major events ruptured about2/3 of the whole length of the northern boundary of the Bayan Har block. At the same time, the sequence has the characteristics of accelerating strain release and gradually shortening intervals between events, suggesting that the movement of the block has been speeding up since 1902 at the latest. As a response to this speeding-up movement, a sequence of 3 major events have occurred on the eastern boundary of the block since about 1933, which has also the characteristics of accelerating strain release and gradually shortening intervals between events. The 2008 Wenchuan earthquake is the most-recent event in the response sequence. The factor that the occurrence of the response sequence of major earthquakes on the eastern boundary is delayed for decades at least behind the sequence on the northern boundary would be associated with the non-rigid motion of the block. In addition, it is found that the event′s order-number versus time relationships of the two sequences of major earthquakes are helpful in analyzing the mid- and long-term seismic potentials for the northern and eastern boundaries of the Bayan Har block.%2008年汶川地震发生在巴颜喀拉块体的东边界.为了探讨区域动力学背景与该地震发生的关系,本文基于活动构造、震源机制解、GPS站速度、地震破裂展布以及历史大地震活动等资料分析巴颜喀拉块体北、东两个边界断裂系统的运动、变形以及大地震序列发生的关联性.结果表明:由于受到华南地块的阻挡,巴颜喀拉块体朝东-南东方向的"逃逸"运动一表现为该块体北边界的左旋走滑断层作用-在该块体的东边界转换成为逆冲或缩短兼走滑断层作用,亦即该块体的运动对其东边界断裂系统具有显著的"加载"作用.这种加载作用也反映在该块体北和东两个边界大地震序列发生的关联性上.19世纪中-晚期至2001年期间,一个由8次事件组成的大地震序列使巴颜喀拉块体北边界总长度的2/3破裂,该序列同时具有加速应变释放以及事件的间隔逐渐缩短的特征,反映最晚自1902年以来该块体发生了加速运动.作为对这一加速运动的响应,巴颜喀拉块体东边界大约自1933年以来发生一个由3次事件组成的大地震序列,也显示出加速释放以及事件的间隔逐渐缩短的特征;2008年汶川地震正是该响应序列中的最新事件.东边界的响应型大地震序列的发生至少滞后于北边界的数十年,可能与该块体的非刚性运动有关.另外,这两个大地震序列的事件序次-时间关系有助于分析该块体北与东边界的中-长期地震危险性.
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