阿尔金断裂乌尊硝尔段古地震复发特征与级联破裂行为研究

The Altyn Tagh fault is a left-lateral active fault along the northern boundary of Tibet Plateau and one of the few giant strike-slip faults in the world. Most sections of the fault preserved clear seismic surface ruptures, but there are no strong earthquakes producing surface ruptures recorded in histories. Although some paleoseismic studies have been conducted in recent decades, the lack of long sequence paleoseismic records limits the more accurate understanding of the recurrence characteristics of paleoearthquakes. This application intends to select the pull-apart basin, with high deposition rate and strong rhythmic strata, in the Wuzunxiaoer section to excavate a large three-dimensional trench, and determine the accurate paleoseismic event horizon through the interpretations of the strata and their deformations of strong earthquakes. The long series of earthquake records will be established by combining carbon and luminescence dating methods, showing the recurrence characteristics of paleoearthquakes. On this basis, the spatio-temporal images of strong earthquake rupture will be constructed by comparing with the adjacent paleoseismic sequences to test the blocking ability of barrier structures under different seismic cycles, and discussing the possibility of cascade rupture along different sections of the Altyn Tagh fault.

阿尔金断裂是位于青藏高原北部边界的一条左旋走滑断裂，也是世界上少有的巨型活动走滑断裂之一。沿断裂大部分段落保存有清晰的地震地表破裂遗迹，但历史上并未记录到形成地表破裂的强震事件。虽然近几十年来开展了一些古地震研究工作，但长序列古地震记录的匮乏，限制了对其古地震复发特征更为准确的认识。本申请拟选择乌尊硝尔段保存有高沉积速率和强韵律地层的拉分盆地开展研究，通过布设大型三维古地震探槽，对探槽地层及强震相关变形进行精细解译，确定准确的古地震事件层位；结合碳十四和光释光测年技术，限定古地震事件年龄，建立古地震事件的长序列，进而确定古地震复发规律。以此为基础，通过与相邻段古地震序列的对比，构建区域强震破裂时空图像，检验不同地震轮回中障碍构造阻挡强震破裂扩展的能力，探讨阿尔金断裂发生级联破裂的可能性。

阿尔金断裂是世界上少有的几条巨型活动走滑断裂带之一，对其古地震复发特征至今认识不足，与缺少高分辨率地层控制下的古地震记录有关。在阿尔金断裂中段乌尊硝尔附近发育的小型拉分盆地内，开展了精细的古地震探槽工作。高分辨率沉积地层记录了丰富的古地震变形及其沉积响应。基于裂缝充填、地层增厚、角度不整合、褶皱等古地震判别标志，共识别了9次古地震事件。结合14C测年技术，约束了9次事件的发生时间，分别为AD1223~1763 (事件WZ1)、384~184BC (事件WZ2)、417~218BC (事件WZ3)、1438~590BC (事件WZ4)、3535~1517BC (事件WZ5)、4560~3604BC (事件WZ6)、5119~4816BC (事件WZ7)、5300~5106BC 事件(WZ8)、5605~5325BC (事件WZ9)。古地震复发周期为869±666 yr，变异系数为0.77，显示为弱周期性，复发间隔从76年至1762年不等。通过与相邻的、平顶山阶区以东的探槽中古地震数据对比，发现平顶山阶区两侧在发生的级联破裂的概率最高为0.33，高于有限元数值模拟的结果。