| 汶川地震和芦山地震的孕震机理及震前中长期地震危险性研究 |
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| 引用本文： | 林邦慧,陈祖安,白武明,程旭.汶川地震和芦山地震的孕震机理及震前中长期地震危险性研究[J].地震学报,2018,40(3):279-290. |
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| 作者姓名： | 林邦慧 陈祖安 白武明 程旭 |
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| 作者单位： | 1.中国北京 100081 中国地震局地球物理研究所 |
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| 基金项目： | 国家自然科学基金（41090291）资助 |
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| 摘 要： | 运用非连续变形分析法与三维有限元法相结合的方法，以GPS资料作为位移速率和震源机制的约束条件，通过数值模拟研究了青藏高原及其东侧邻区构造地块的运动、变形、相互作用及其与近30年来发生于该区的大地震之间的关系。研究中引入了以应力与摩擦强度的比值定义的断层“失稳危险度”，通过数值模拟计算得到了研究区地壳块体边界断层的失稳危险度分布。结果表明，失稳危险度高的地段与近期该区发生的MS≥7.0地震所在的位置基本一致，其中龙门山断裂带上包括汶川和芦山大地震的发震断层均为失稳危险度最高值地区。计算得到的应变率强度分布图显示，青藏高原东部边缘整条地带均为应变率强度的陡变带，特别是以龙门山断裂带上的陡变最为明显，其西侧应变率强度为东侧的近4倍，而且，这个带位于宽度相同、走向与龙门山断裂带走向相一致的高应变能密度带中，表明这两次大地震前，作为其发震断层的龙门山断裂带已积累了相当高的应变能，失稳危险度高，处于力学上的不稳定状态。模拟计算得到在上地壳层中，2001年昆仑山口西MS8.1地震引起汶川、芦山地震发震断层的库仑破裂应力增加约0.016 MPa，相当于龙门山断裂带约两年的应力积累，也就是说，使汶川、芦山地震发震断层的失稳破裂提前了约两年。 此外，关于2008年汶川MS8.0地震的模拟计算表明，汶川地震的发生也使包括芦山地震发震断层的龙门山断裂带西南段和东昆仑断裂带东南端的库仑破裂应力增大，应变能积累增强，这说明汶川MS8.0地震的发生对已处于失稳危险度较高状态的2013年芦山地震和2017年九寨沟地震发震断层的提前失稳破裂起到了促进作用。
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| 关 键 词： | 汶川地震 芦山地震 孕震机理 中长期地震危险性 非连续变形分析法 有限元法 |
| 收稿时间： | 2018-02-14 |
Seismogenic mechanism and the intermediate- and long-term earthquake risks of the 2008 Wenchuan and 2013 Lushan earthquakes |
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| Institution: | 1.Institute of Geophysics，China Earthquake Administration，Beijing 100081，China2.Institute of Geology and Geophysics，Chinese Academy of Sciences，Beijing 100029，China3.Institute of Earthquake Forecasting，China Earthquake Administration，Beijing 100036，China |
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| Abstract: | The 3D finite element method （FEM） and the discontinuous deformation analysis （DDA） were combined , with constraints from GPS data and focal mechanisms, to simulate numerically the movement, deformation and interaction of the tectonic blocks system of the Qinghai-Tibetan Plateau and its vicinity, and their correlation with the occurrence of the recent MS≥7.0 earthquakes in this area. An " instability risk factor”, defined as the ratio of the normal stress to the friction strength, was introduced to characterize the degree of the instability risk on the boundary faults of the tectonic blocks in the studied region. The simulation shows the spatial coincidence between the segments of the boundary faults of the tectonic blocks with higher instability risk factors and the locations of the recent significant earthquakes in the studied areas. Particularly, the Longmenshan fault zone, where the 2008 Wenchuan and 2013 Lushan earthquakes occurred, is the fault zone with high instability risk factor. The calculation results indicate that the eastern boundary of the Qinghai-Tibetan Plateau is a fault zone of steepest strain-rate with strain-rate in the west side four times as high as that in the east side. Meanwhile, it is found that the eastern boundary of the Qinghai-Tibetan Plateau is also a high strain-energy zone with same trend and width as the Longmenshan fault zone. These results indicate that before the occurrence of the 2008 Wenchuan and 2013 Lushan earthquakes, relative high strain energy have already accumulated in the seismogenic fault of the 2008 Wenchuan earthquake, and these seismogenic faults have been in highly instability state mechanically. It is estimated that the occurrence of the 2001 western Kunlun Mountain Pass earthquake increased the Coulomb failure stress by about 0.16 MPa, a value corresponding to two years stress accumulation on the seismogenic fault, thus promoting the occurrence of the 2008 Wenchuan and 2013 Lushan earthquakes two years in advance. Based on the simulations after the 2008 Wenchuan earthquakes, it is found that the occurrence of the 2008 Wenchuan earthquake increased the Coulomb failure stress in the southwestern segment of the Longmenshan fault zone and southeastern segment of the eastern Kunlun fault zone, which indicates that the occurrence of the 2008 Wenchuan earthquake has promoted the occurrence of 2013 Lushan earthquake and the 2018 Jiuzhaigou earthquake. |
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