汶川地震前龙门山及其周缘断裂形变运动与应力累积的数值模拟

发布时间：2019-06-05 21:40

【摘要】：为揭示汶川地震前龙门山及其周缘断裂的形变与应力累积状态,文中构建了包含龙门山、龙日坝、岷江和虎牙4条断裂的三维黏弹性有限元模型,以1999—2004年GPS结果为约束,模拟了龙门山断裂带及其周缘区域的形变运动。得到以下结论:1)平行于龙门山断裂带的速度分量主要被龙日坝断裂吸收,垂直于龙门山断裂带的速度分量主要被其自身吸收;岷江和虎牙断裂对龙门山断裂带北段起到一定的屏障作用,导致其北段压缩量明显低于南段。2)沿龙门山断裂带由SW向NE方向延伸,主压应力与断层走向的夹角由接近垂直逐步转至约45°;断层南段挤压、剪切应力累积速率高,且压应力大于剪应力,北段应力累积速率低,压应力与剪应力接近。这与龙门山断裂带SW段中小地震频发、地震活动强烈,NE段偶有小震、地震活动微弱相吻合;也与汶川M_S8.0地震逆冲兼具右旋走滑、芦山M_S7.0地震逆冲破裂的方式相一致。3)假设发生震级、类型相同的地震所需应力积累量相同,那么研究区内岷江断裂、龙门山断裂南段和虎牙断裂破裂以逆冲运动为主,3条断裂的地震复发周期依次变长;龙日坝断裂北段和龙门山断裂北段以逆冲兼具右旋走滑为主,前者地震复发周期短于后者;龙日坝断裂南段则以纯右旋走滑为主,地震复发周期有可能最短。
[Abstract]:In order to reveal the deformation and stress accumulation of Longmenshan and its surrounding faults before Wenchuan earthquake, a three-dimensional Viscoelastic finite element model including Longmenshan, Longriba, Minjiang and Huya faults is constructed in this paper, which is constrained by GPS results from 1999 to 2004. The deformation movement of Longmenshan fault zone and its surrounding area is simulated. The conclusions are as follows: 1) the velocity components parallel to the Longmenshan fault zone are mainly absorbed by the Longriba fault, and the velocity components perpendicular to the Longmenshan fault zone are mainly absorbed by the Longmenshan fault zone; Minjiang and Huya faults play a certain role as a barrier to the northern section of Longmenshan fault zone, which leads to the compression of the northern segment of Longmenshan fault zone is obviously lower than that of the southern segment. 2) the Longmenshan fault zone extends from SW to NE along the Longmenshan fault zone. The angle between principal compressive stress and fault strike gradually changes from close to vertical to about 45 掳. In the south section of the fault, the accumulation rate of shear stress is high, and the compressive stress is higher than the shear stress, while the stress accumulation rate in the north section is low, and the compressive stress is close to the shear stress. This is consistent with the frequent occurrence of small and medium earthquakes and strong seismic activity in SW section of Longmenshan fault zone, and the occasional small earthquakes in NE section, and the weak seismic activity. It is also consistent with the right-handed strike-slip of Wenchuan M_S8.0 earthquake thrust, and the mode of thrust rupture of Lushan M_S7.0 earthquake is consistent. 3) assuming that the magnitude of the earthquake occurs, the stress accumulation of the same type of earthquake is the same, then the Minjiang fault in the study area, The rupture of Longmenshan fault and Huya fault is dominated by thrust movement, and the recurrence period of the three faults becomes longer in turn. The north section of Longriba fault and the northern section of Longmenshan fault are dominated by thrust and right-handed strike-slip, the recurrence period of the former is shorter than that of the latter, and the southern section of Longriba fault is dominated by pure right-handed strike-slip, and the recurrence period of the earthquake may be the shortest.
【作者单位】：中国地震局第一监测中心;防灾科技学院;山东省地震局;
【基金】：国家自然科学基金(41472180) 中国地震局第一监测中心科技创新主任基金(FMC2017012) 震情跟踪定向工作(2017010208)共同资助
【分类号】：P315.2

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