关键词: 古地震, 深槽, 大凉山

Abstract: 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.

Key words: Daliangshan, Trenching, Paleo-earthquake