Abstract:

The Dengdengshan and Chijiaciwo faults situate in the northeast flank of Kuantanshan uplift at the eastern terminal of Altyn Tagh fault zone, striking northwest as a whole and extending 19 kilometers and 6.5 kilometers for the Dengdengshan and Chijiaciwo Fault, respectively. Based on satellite image interpretation, trenching, faulted geomorphology surveying and samples dating etc., we researched the new active characteristics of the faults. Three-levels of geomorphic surfaces, i.e. the erosion rock platform, terrace I and terrace Ⅱ, could be found in the northeast side of Kuantanshan Mountain. The Dengdengshan Fault dislocated all geomorphic surfaces except terrace I, and the general height of scarp is about 1.5 meters, with the maximum reaching 2.6 meters. Three paleoseismic events are determined since late Pleistocene through trenching, and the total displacement of three events is about 2.7 meters, the average vertical dislocation of each event changed from 0.5 to 1.2 meters. By collecting age samples and dating, the event Ⅰ occurred about 5ka BP, event Ⅱ occurred about 20ka BP, and event Ⅲ occurred about 35ka BP. The recurrence interval is about 15ka BP; and the vertical slip rate since the late Pleistocene is about 0.04mm/a.
The Chijiaciwo Fault, however, dislocated all three geomorphic surfaces, and the general scarp height is about 2.0 meters with the maximum up to 4.0 meters. Three paleoseismic events are determined since late Pleistocene through trenching, and the total displacement of three events is about 3.25 meters, the average vertical dislocation of each event changed from 0.75 to 1.5 meters, and the vertical slip rate since the late Pleistocene is about 0.06mm/a. Although the age constraint of paleoearthquakes on Chijiaciwo Fault is not as good as that of Dengdengshan Fault, the latest event on Chijiaciwo Fault is later than Dengdengshan Fault's. Furthermore, we infer that the recurrence interval of Chijiaciwo Fault is 15ka BP, which is close to that of Dengdengshan Fault.
The latest event on Chijiaciwo Fault is later than the Dengdengshan Fault's, and the vertical displacement and the slip rate of a single event in late Quaternary are both larger than that of Dengdengshan Fault. Additionally, a 5-kilometer-long discontinuity segment exists between these two faults and is covered by Quaternary alluvial sand gravel. All these indicate that the activity of the Chijiaciwo Fault and Dengdengshan Fault has obvious segmentation feature.
The size of Chijiaciwo Fault and Dengdengshan Fault are small, and the vertical slip rate of 0.04~0.06mm/a is far smaller than that of Qilianshan Fault and the NW-striking faults in Jiuxi Basin. All these indeicate that the tectonic deformation of this region is mainly concentrated on Hexi Corrider and the interior of Tibet Plateau, while the activties of Chijiaciwo and Dengdengshan faults are characterized by slow slip rate, long recurrence interval(more than 10ka)and slow tectonic deformation.

Key words: Altyn Tagh fault zone, Dengdengshan Fault, Chijiaciwo Fault, slip rate, paleoearthquake

摘要：

登登山-池家刺窝断裂位于阿尔金断裂东端宽滩山隆起的NE侧，总体走向NW，地貌上表现为醒目的断层陡坎；登登山段长约19km，池家刺窝段长约6.5km。通过卫星影像解译、探槽开挖、断错地貌测量及年龄样品测试等工作，研究了2条断裂的新活动特征。宽滩山NE麓普遍发育3级地貌面，即山前基岩侵蚀台面和冲沟I、Ⅱ级阶地。登登山断裂断错除I级阶地以外的其他地貌面，陡坎高度普遍在1.5m左右，最大高度2.6m。探槽揭露登登山断裂晚更新世以来有3次古地震事件，3次事件的总断距约2.7m，一次事件的垂直断距为0.5~1.2m，事件Ⅰ大约发生于距今5ka；事件Ⅱ大致发生于距今2×10⁴a，事件Ⅲ大致发生于距今3.5×10⁴a，重复间隔约1.5×10⁴a，晚更新世以来的垂直滑动速率约为0.04mm/a。
池家刺窝断裂断错了所有3级地貌面，陡坎最大高度为4m，一般在2m左右。探槽揭露池家刺窝断裂晚更新世以来也有3次古地震事件，3次事件的总断距约3.25m，1次事件的垂直位错为0.75~1.5m，晚更新世以来断裂垂直滑动速率为0.06mm/a。池家刺窝断裂古地震事件年代限定较差，但最新1次事件晚于登登山断裂，根据登登山断裂古地震事件的研究结果，推测池家刺窝断裂古地震重复间隔接近于登登山断裂的1.5×10⁴a左右。
池家刺窝断裂的最新活动时代晚于登登山断裂，1次事件的垂直位错及晚更新世以来的垂直滑动速率都比登登山断裂略大，2条断裂之间还有长约5km的不连续段，被第四纪冲洪积砂砾石层覆盖，地形平坦，断裂地貌特征不发育，这些都表明登登山断裂和池家刺窝断裂具有明显的分段活动特征。阿尔金断裂以北的登登山和池家刺窝断裂规模都不大，垂直滑动速率仅为0.04~0.06mm/a，远小于祁连山断裂及酒西盆地内NW向断裂的垂直滑动速率，反映出构造变形主要限制在高原内部及河西走廊地区，登登山和池家刺窝断裂以低滑动速率、古地震复发间隔很长（>10⁴a）的缓慢构造变形为特征。

关键词: 阿尔金断裂, 登登山断裂, 池家刺窝断裂, 滑动速率, 古地震