四川青川县乔庄镇城区活动断裂探测与评价

Active Fault Surveying and Assessment of Qiaozhuang Town,Qingchuan County,Sichuan Province

青川县乔庄镇主城区坐落于乔庄河Ⅰ级河流阶地面上,平武-青川断裂分为3支呈隐伏状穿过主城区,地表未见明显的断裂新活动形迹。2008年5月12日发生的汶川MS8.0级地震,对青川县乔庄镇造成了比较严重的破坏,出现了沿平武-青川主干断裂通过位置震害显著加重的条带状异常现象,但未见明显的地表破裂。本文在地面地质调查、浅层地球物理勘探和探槽开挖验证结果的基础上,对平武-青川断裂在乔庄镇主城区的通过位置进行了重新定位,定位结果与前人研究结果存在一定的差异。结合地表调查发现的零星地表破裂和探槽下部砂砾石层出现的小尺度变形及位错现象分析,乔庄镇条带状震害加重异常现象应是平武-青川断裂在汶川地震时发生的近地表错动所致。由此联系到汶川地震的余震条带与平武-青川断裂乔庄以东段基本重合的事实,平武-青川断裂的活动性应是下一步研究工作的方向。

Qiaozhuang town of Qingchuan county is located on the terrace I of the Qiaozhuang river,where Pingwu-Qingchuan fault consists of three buried fault segments,crossing the main area of Qiaozhuang town.There are not new active evidence of the fault found on the ground.On May 12 of 2008,the Wenchuan earthquake caused serious damages to the city zone of Qiaozhuang town.The damages,along the main fault zone of the Qingchuan fault,are more serious and engendered a abnormal damage belt.However,there is no obvious surface rupture caused in the ground.Through geological investigation,shallow geophysical exploration and trenching,the segments of Pingwu-Qingchuan fault in the city zone were repositioned.Through some surface rupture and the slight deformation and offset of the sand-gravel layer under the trench,we proposed that the abnormal damage belt in Qiaozhuang town was due to the near-surface offset of the Pingwu-Qingchuan fault caused by the Wenchuan earthquake.This is consistent with the fact that the aftershock belt of the Wenchuan earthquake extend to the eastern segment of Pingwu-Qingchuan fault.Therefore,more work should be done for the new activity of Pingwu-Qingchuan fault in the future.