四川大凉山断裂带古地震研究初步结果

PRELIMINARY RESULTS OF THE INVESTIGATION OF PALEO-EARTHQUAKES ALONG THE DALIANGSHAN FAULT ZONE, SICHUAN PROVINCE, CHINA

沿四川大凉山断裂带的 4条次级断裂开挖了 4个探槽 ,共揭露出 9次古地震事件。根据探槽中年龄样品的测试结果 ,分析了各次事件的距今年龄及其重复间隔。其中 ,有 3个探槽共揭露出4次全新世以来的古地震事件。 9次古地震的垂直位移量在 0 5～ 1 5m之间 ,与鲜水河 -小江断裂带历史地震所产生的垂直位移量进行对比 ,估计它们的震级都在

Four prospecting trenches were excavated along 4 subsidiary faults of the Daliangshan fault zone, and 9 paleo-seismic events were revealed by these trenches. West of Doukanzi village, the Tc-1 trench is located on the northern segment of the Shimian-Haitang-Yuexi subsidiary fault. The occurrence time of 2 paleo-earthquakes revealed by this trench is 35ka and 3.5ka, respectively. In the north of Keqilada village, the Tc-2 trench is located on the middle-northern segment of the Puxiong-Zhuhe subsidiary fault. The occurrence time of 2 paleo-seismic events revealed by this trench is 28～30ka and 24ka, respectively. The trench Tc-3 in the south of Tuodu village is located on the middle-northern segment of the Tuodu-Butuo subsidiary fault. The occurrence time of 3 paleo-earthquakes revealed by this trench is 25ka, 10ka and 7.5ka, respectively. The trench TC-4 at Cizijiao village is located on the northern segment of the Jifulada-Jiaojihe subsidiary fault, and the occurrence time of 2 paleo-seismic events revealed by this trench is 15ka and 4.5ka. Among the 9 events, 4 events occurred in Holocene time. The occurrence of the 9 events indicates that the Daliangshan fault zone has been active since late Pleistocene. The vertical displacements produced by these 9 earthquakes are 0.5～1.5m. In comparison to the displacement produced by the historical earthquakes along the Xianshuihe-Xiaojiang fault zone, it can be postulated that the maximum magnitude of these 9 events is M≥7. The study of fault segmentation has shown that a major fault zone can be divided into several segments with independent rupturing history. The segments are separated from each other by relatively large scale bending, turning, crossing and step-over, which may effectively inhibit the propagation of the rupture. The four subsidiary faults of the Daliangshan fault zone are 60～90km in length, and the width of the step-over zone between two subsidiary faults is 5～15km, which is wide enough to inhibit the propagation of rupture on the adjacent faults. That is why the subsidiary faults become an independent rupturing unit. It is concluded, therefore, that the paleo-seismic events revealed by the 4 trenches were independent rupturing events.