利用近场高频GPS、 强地面运动和远场地震波形数据联合反演2008年汶川MS8.0地震的震源时空破裂过程

摘要/Abstract

摘要： 联合近场GPS测站1-Hz运动学位移、强震仪加速度波形和全球台站P震相波形作为约束, 以时空滑动分布约束条件和ABIC模型参数选择方法, 结合先验的滑动方向变化范围, 反演2008年汶川M_S8.0地震的震源时空破裂过程, 给出了能够综合反映震源破裂过程的统一模型。结果表明, 汶川地震总体上存在4个主要的破裂区, 最主要的一个破裂区位于震源东北40~120 km, 断层面上的最大位错量约为10 m, 主体滑动分布在2~20 km深度范围, 破裂达到地表; 第二个主体破裂区位于断层破裂带南段, 最大滑动量达到6 m; 另外2个主体滑动区位于断层破裂带北段, 但滑动破裂量小于断层南段破裂区的滑动量, 滑动破裂值最大值为4 m, 超过1 m的区域在走向上超过70 km。反演得到的断层滑动模型的地震矩为9.5×10²¹ Nm, 相应的矩震级为M_W7.95。汶川地震破裂表现为单侧破裂, 起始破裂在汶川下方16 km深度, 向东北方向一致性地传播, 过程持续~120 s。在地震发生后0~10 s内, 破裂集中在震源起始破裂区, 滑动破裂值为~1.0 m, 之后破裂向东北方向扩展, 震后20~40 s是主要的破裂时段。在40~60 s, 破裂跨越断层南段和北段。在80~90 s破裂最大值开始下降, 在100~110 s时, 下降为~0.5 m, 在110~120 s时, 下降为~0.1 m。加入近场GPS测站1-Hz 波形数据与近场强震仪波形和远场长周期体波联合反演, 提高了震源破裂模型的空间分辨率, 特别是浅部滑动破裂区的分辨率, 反演的最大滑动破裂值比不用1-Hz 波形数据反演的结果增大, 表明近场1-Hz GPS波形数据对于揭示汶川地震的时空破裂过程具有重要的作用。

关键词: 2008汶川M_S8.0地震, 高频GPS, 强地面运动, 震源破裂模型, 同震变形

Abstract: The rupture process of the 2008 Wenchuan M_S8.0 earthquake is derived by joint inversion using near-field 1-Hz GPS, strong motion waveforms and the P-phase seismograms recorded by the Global Seismographic Network stations, considering the constrained conditions of spatial-temporal slip, ABIC criterion and a priori constraints on the rupture slip directions. A unified source model is obtained, which reflects multiple aspects of the rupture process of the Wenchuan earthquake. The inversion results show that there are 4 dominant rupture zones. The first one is 40~120 km northeastward away from the focus with maximum slip value at ~10 m, and major slips are in the depth of 2~20 km, with rupture reaching to the surface. The second primary slip zone is also located at southern segment of the Longmenshan fault, with maximum slip value at ~6 m. The other two primary slip zones are at the northern segment of the Longmenshan fault, with smaller maximum slip values at 4 m. The length of the rupture zones of slip values more than 1 m is larger than 70 km in the strike direction. The estimated seismic moment is 9.5×10²¹ Nm, with a moment magnitude equivalent to M_W7.95. Snapshots of the rupture process demonstrate that the Wenchuan earthquake ruptured unilaterally, initiated at the depth of 16 km beneath Wenchuan zone, and propagated consistently northeastward, with an entire rupture duration of ~120 seconds. During the 0~10 seconds after the initiation, the slip is dominant around the earthquake focus, with slip values around ~1.0 m, and then the rupture continued to propagate northeastward. The duration of 20~40 seconds is a primary temporal period of rupture. In the period of 40~60 seconds, the rupture propagated to the intersection of the southern and northern segments of the Longmenshan fault. During the 80~90 seconds, the maximum slip values began to decrease. During the 100~110 seconds, slip decreased to ~0.5 m. During the 110~120 seconds, slip decreased to ~0.1 m. The addition of near-field 1-Hz GPS waveforms to the inversion of strong motion and teleseismic P-phase seismograms can increase the resolution of rupture slip models, especially for the shallow zones, with a slightly larger maximum slip values than the inversion result without 1-Hz GPS waveforms involved.

Key words: The 2008 Wenchuan M_S8.0 earthquake, High-rate GPS, Rupture model of earthquake source, Coseismic deformation

中图分类号:

P315.7

孟国杰, 苏小宁, 王振, 廖华. 利用近场高频GPS、强地面运动和远场地震波形数据联合反演2008年汶川M_S8.0地震的震源时空破裂过程[J]. 地震, 2018, 38(2): 11-27.

MENG Guo-jie, SU Xiao-ning, WANG Zhen, LIAO Hua. Joint Inversion for the Rupture Process of the 2008 Wenchuan M_S8.0 Earthquake from 1 Hz GPS, Strong Motion and Teleseismic Data[J]. EARTHQUAKE, 2018, 38(2): 11-27.

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