Abstract: As the northeast boundary of the Tibetan plateau, the Haiyuan-Liupan Shan fault zone has separated the intensely tectonic deformed Tibetan plateau from the stable blocks of Ordos and Alxa since Cenozoic era. It is an active fault with high seismic risk in the west of mainland China. Using geology and geodetic techniques, previous studies have obtained the long-term slip rate across the Haiyuan-Liupan Shan fault zone. However, the detailed locking result and slip rate deficit across this fault zone are scarce. After the 2008 Wenchuan M_S8.0 earthquake, the tectonic stress field of Longmen Shan Fault and its vicinity was changed, which suggests that the crustal movement and potential seismic risk of Haiyuan-Liupan Shan fault zone should be investigated necessarily.
Utilizing GPS horizontal velocities observed before and after Wenchuan earthquake(1999~2007 and 2009~2014), the spatial and temporal distributions of locking and slip rate deficit across the Haiyuan-Liupan Shan fault zone are inferred. In our model, we assume that the crustal deformation is caused by block rotation, horizontal strain rate within block and locking on block-bounding faults. The inversion results suggest that the Haiyuan fault zone has a left-lateral strike-slip rate deficit, the northern section of Liupan Shan has a thrust dip-slip rate deficit, while the southern section has a normal dip-slip rate deficit. The locking depths of Maomao Shan and west section of Laohu Shan are 25km during two periods, and the maximum left-lateral slip rate deficit is 6mm/a. The locking depths of east section of Laohu Shan and Haiyuan segment are shallow, and creep slip dominates them presently, which indicates that these sections are in the postseismic relaxation process of the 1920 Haiyuan earthquake. The Liupan Shan Fault has a locking depth of 35km with a maximum dip-slip rate deficit of 2mm/a. After the Wenchuan earthquake, the high slip rate deficit across Liupan Shan Fault migrated from its middle to northern section, and the range decreased, while its southern section had a normal-slip rate deficit.
Our results show that the Maomao Shan Fault and west section of Laohu Shan Fault could accumulate strain rapidly and these sections are within the Tianzhu seismic gap. Although the Liupan Shan Fault accumulates strain slowly, a long time has been passed since last large earthquake, and it has accumulated high strain energy possibly. Therefore, the potential seismic risks of these segments are significantly high compared to other segments along the Haiyuan-Liupan Shan fault zone.

Key words: Haiyuan-Liupan Shan fault zone, locking, creep, slip rate deficit, GPS

摘要： 利用青藏高原东北缘及周缘地区1999-2007年和2009-2014年2个时段的GPS水平运动速度场做约束，反演获取了海原-六盘山断裂带的闭锁程度和滑动速率亏损的时空分布演化。结果表明，海原断裂带以左旋走滑亏损为主，六盘山断裂北段以逆冲倾滑速率亏损为主，南段则以正向倾滑为主。其中，毛毛山断裂和老虎断裂西段在2个时段的闭锁深度都达到25km，最大左旋滑动亏损为6mm/a。老虎山东段和海原断裂（狭义）闭锁程度低，主要处于蠕滑状态。六盘山断裂2个时段的闭锁深度可达35km，最大逆冲滑动速率亏损为2mm/a。汶川地震后，六盘山断裂上逆冲滑动速率亏损高值区由中段迁移至北段且范围减小，南段则变成正倾滑速率亏损。毛毛山、老虎山西段和六盘山断裂的地震危险性要明显高于海原-六盘山断裂带其他断层段。

关键词: 海原-六盘山断裂带, 闭锁, 蠕滑, 滑动速率亏损, GPS