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2008年5月12日,汶川Mw7.9级地震在青藏高原东缘沿龙门山逆冲断裂带中段形成了两条NE向和一条NW向逆冲走滑型地表破裂。依据同震地表陡坎形态特征,将其分为8种类型:逆断层陡坎、上盘垮塌陡坎、挤压推覆陡坎、右旋挤压推覆陡坎、断层相关褶皱陡坎、后冲挤压陡坎、上冲叠覆陡坎和局部正断层陡坎。汶川地震所形成的同震地表破裂主要由以逆冲为主的映秀破裂段和兼具逆冲、右旋走滑的北川破裂段两部分组成,这两个破裂段分别对应于Mw7.8与Mw7.6级地震事件;它们还可进一步细分为分别对应于Mw7.5、Mw7.7、Mw7.0和Mw7.5等4个次级事件的4个次级破裂段。这些次级破裂段的级联破裂可以用来解释为什么汶川地震的持续时间长达110 s。余震震源机制分析结果表明,发震断层的倾角随深度的增加而变缓,且从西南向北东逐渐变陡可以用来解释走滑分量增加的成因。此次大地震还表明,沿青藏高原东缘地形抬高的主要驱动力可能是地壳挤压缩短,而不一定是下地壳物质流动和膨胀引起上地壳的隆升。
On May 12, 2008, the Wenchuan Mw7.9 earthquake formed two NE-trending and NW trending thrust strike-slip surface ruptures in the middle segment of the Longmenshan thrust belt along the eastern Qinghai-Tibetan Plateau. According to the morphological characteristics of the surface steep ridge of the coseismic surface, they are divided into eight types: reverse fault scarp, upper wall collapse scarp, extrusion nappe scarp, dextral extrusion thrust scarp, fault-related fold scarp, Backcrop extrusion scarp, upshift overlap scarp and local normal fault scarp. The coseismic surface rupture formed by the Wenchuan earthquake is mainly composed of the Yingxiu fracture zone dominated by thrusting and the Beichuan fracture zone both thrusting and dextral strike-slip. These two fractures correspond to Mw7.8 and Mw7.6 earthquake event; they can be further subdivided into four secondary rupture segments respectively corresponding to four secondary events of Mw7.5, Mw7.7, Mw7.0 and Mw7.5. The cascade rupture of these secondary rupture segments can be used to explain why the Wenchuan earthquake lasted for 110 s. The aftershock focal mechanism analysis shows that the dip angle of the seismogenic fault decreases with the increase of depth, and gradually steep from southwest to northeast can be used to explain the cause of the increase of strike slip component. The major earthquake also showed that the main driving force for elevation along the eastern edge of the Tibetan Plateau may be shortening of crustal crustal extrusion rather than uplift of the upper crust caused by the flow and expansion of the lower crustal material.