【作者】 陈棋福； 华诚； 李乐； 程晋；

【Author】 CHEN Qi-Fu;HUA Cheng;LI Le;CHENG Jin;Key Laboratory of Earth and Planetary Physics,Institute of Geology and Geophysics,Chinese Academy of Sciences;Department of Mechanics and Engineering Science,Fudan University;Key Laboratory of Earthquake Prediction,Institute of Earthquake Science,China Earthquake Administration;School of Mathematical Sciences,Fudan University;

【机构】 中国科学院地质与地球物理研究所中国科学院地球与行星物理重点实验室； 复旦大学力学与工程科学系； 中国地震局地震预测研究所(地震预测重点实验室)； 复旦大学数学科学学院；

【摘要】 根据龙门山断裂带地区的主要构造特征,建立该地区的有限元模型,同时考虑地下深处的黏弹性蠕动和不同部位间的接触关系,模拟计算了研究区在强震轮回活动中的时间演化历程.模拟结果表明:龙门山断裂带深处的滑动速率比浅表的滑动速率大,龙门山断裂带周围是相对容易发生应变积累的地区,其5~19 km深度也是高应力聚集成核区,随时间推移的应力集中程度加剧而引发强震.本模拟分析证实了重复地震观测所揭示的龙门山断裂带存在深浅活动速率差异的现象,这在一定程度上可以解释出乎预料的汶川M_w7.9地震的孕育机理.综合分析研究提出:应充分利用重复地震这一天然的"地下蠕变计(subsurface creepmeter)"来探测深部构造变形的活动,为强震危险性分析提供必要的"原位(in situ)观测"约束信息.更多还原

【Abstract】 The 2008 M_w7.9 Wenchuan earthquake ruptured the middle and northern segments of the Longmenshan faults zone(LMSFZ) at the eastern margin of the Tibetan Plateau.Prior to this earthquake,the LMSFZ had been seismically quiet for several centuries,where no hints suggest such a M~8.0 earthquake might strike the area.The long-term geological investigations and short-term geodetic measurements before the Wenchuan earthquake generally agree that the horizontal slip rate along the LMSFZ is very limited.The low deformation rate observed at the surface around the LMSFZ may not reflect the true deep deformation where the devastating Wenchuan earthquake nucleated.The slip rates at depth derived from seismological investigation of repeating microearthquakes were found to be systematically larger than those observed on the surface.In order to validate the depth-related slip rate pattern,based on regional tectonic characteristics of the LMSFZ,a two-dimensional viscoelastic finite-element model with contact algorithm is established to simulate the evolution process of the crust and upper mantle during an earthquake cycle.The viscoelastic creep and discontinuity contact relationships in the crust and upper mantle are taking into account.Our primary results confirm the depth-related lateral slip rate pattern around the LMSFZ revealed by the seismological observations of repeating earthquakes.Furthermore,the LMSFZ and its surrounding regions are prone to accumulation of strain and strain rate potential with the highest stress concentration area of 5~19 km depth,suggesting that this area may essentially nucleate strong earthquakes over time,depending on the bilateral rheology structure of the lower crust and upper mantle.At the same time,the large strain rate accommodated at depth can explain the occurrence of the unanticipated Wenchuan M_w7.9 earthquake in 2008.It is found that the slip deficit area in the northeastern Japan subduction zone estimated from repeating earthquakes is very consistent with the rupture zone of the 2011 M_w 9.0 Tohoku-oki earthquake.We suggest that slip rates at seismogenic depths are of critical importance in seismic hazard analysis.The reoccurrence frequency of repeating earthquakes can be regarded as the "subsurface creepmeters" to measure the in-situ deep slip rate of tectonic deformation.更多还原