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赤山地处安徽省泗县东北部,为郯庐断裂带西支断裂通过处。以往研究认为,郯庐断裂带赤山段第四纪以来有较为明显的活动。此次在垂直于赤山段开挖的多个探槽中均揭露出史前地震遗迹(多期逆断型崩积楔),具体表现为断层上盘砖红色上白垩统砂岩或黄白色中更新统砾石层向东叠置于褐黄色中、上更新统黏土之上。在楔状体根部均发现向NW陡倾的断裂,陡立的断面向上转变为缓倾的上翻垮落面。多条探槽揭示的断裂点的连线总体呈NNE走向,断裂通过处的上盘后缘大部分残留了凸起地貌,部分EW向冲沟被断裂右旋扭错。多条探槽两壁都一致显示出从西向东的推挤垮塌痕迹。其中Tc1～Tc4表现为砖红色砂岩(K2)逆冲垮落于黄褐色含铁锰结核黏土(Q2p-3)之上,Tc5则表现为红砂岩(K2)和黄白色砾石层(Q2p)逆冲垮塌于上述的黏土之上。在几个探槽的逆断型崩积楔上均揭示出此段曾有多次逆断型崩积事件发生,个别探槽揭露楔体较少,可能与其所处的位置、揭露深度和剥蚀残存的高度有关。对开挖探槽及光释光测年结果的详细分析初步得出,郯庐断裂带赤山段在中、晚更新世之交曾多次发生大规模逆断型黏滑事件,即曾多次发生史前大地震。
Chishan is located in the northeastern part of Si County, Anhui Province, passing through the western branch of the Tanlu Fault Zone. According to previous studies, there has been more obvious activity since Quaternary in the Chifeng segment of Tancheng-Lujiang fault zone. Prehistoric seismic ruins (multi-stage thrust-type collapse wedges) were uncovered in a number of trenches excavated perpendicular to the Chishan section, and were characterized by the red-upper Cretaceous sandstone or yellow-white middle-Pleistocene The gravel layer is superimposed eastward on the brownish yellow, upper Pleistocene clay. In the wedge root are found to steeply NW rupture, steep section up into a gentle dip up collapse surface. The connection points of breakpoints revealed by multiple trenches showed a general NNE trend. Most of the trailing edges of the hanging wall at the place of fracture left prominent landforms, and part of the EW trenches were broken right-handedly. Multiple trenches on both walls are consistent display of push collapse from west to east traces. Tc1 ~ Tc4 showed that the reddish-brown sandstone (K2) was thrust down above the yellowish brown Mn-bearing nodule clay (Q2p-3), and Tc5 was red sandstone (K2) and yellowish-white gravel layer Collapse above the clay above. Several reverse trenching wedges on several trenches reveal that there have been multiple reverse trenching events during this period. Individual trenches expose fewer wedges, which may be related to their location, depth of exposure and denudation Residual height related. A detailed analysis of the results of the dating of excavated trenches and optical luminescence shows that a large-scale reverse-type stick-slip event has occurred many times in the Chishan section of the Tancheng-Lujiang fault zone during the middle and late Pleistocene times, Prehistoric earthquake occurred.