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2008年9月12日陇南Ms 5.5地震:一个很可能由汶川地震触发的极浅源地震
罗新宇1, 曾祥方2, 董培育3, 周勇4, 魏星5, 程惠红6
2008年5月12日汶川地震对震源周边地区地震活动性造成了影响,其后2008年9月12日在余震区东北端附近发生了甘肃陇南Ms5.5地震。可靠的震源参数是厘清发震机制的关键信息,本文使用三种方法研究了陇南地震的震源参数。使用gCAP方法反演陇南地震的震源机制及深度,得到的节面解为NP1: 150°/45°/81°、NP2: 342°/45°/98°,非双力偶成分为53%,矩心深度为1.6 km,为浅源逆冲型地震。此外,瑞利波振幅谱及InSAR观测的地表形变进一步了测定陇南地震深度,结果表明其确认为浅源地震。在此基础上,计算了汶川地震对陇南地震断层上的库伦应力影响,发现汶川地震对陇南地震发震断层上的库伦应力变化可达30kPa,超过库伦应力触发阈值,表明了汶川地震对陇南地震有着触发作用。
关键词:  陇南地震  震源参数  瑞利波振幅谱  地表形变  库伦应力
The Longnan Ms 5.5 earthquake on September 12, 2008: a very shallow event probably triggered by the Wenchuan earthquake
Luo Xinyu1, Zeng Xiangfang2, Dong Peiyu3, Zhou Yong4, Wei Xing5, Cheng Huihong6
1.School of Earth and Space Sciences,University of Science and Technology of China;2.Institute of Geodesy and Geophysics,Chinese Academy of Sciences;3.Hubei Earthquake Agency;4.Department of Earth and Space Sciences,Southern University of Science and Technology;5.China Earthquake Networks Center;6.CAS Key Laboratory of Computational Geodynamics, University of Chinese Academy of Sciences
The 2008 Wenchuan earthquake has a significant impact on the seismicity of nearby regions. The Longnan earthquake which occurred on September 12th, 2008 in Gansu province was out of the aftershock zone. Reliable source parameters are essential for understanding the seismogenic process of this earthquake. Therefore, three approaches are adopted to study the source parameters of this event. The focal mechanism is obtained with the gCAP method that takes non-Double-Couple (non-DC) component into account. The two fault planes are NP1:150°/45°/81° and NP2:342°/45°/98°, while the non-DC component is about 53%. The focal depth is 1.6 km, which indicates the Longnan earthquake is a shallow event. Furthermore, this result is also in good agreement with results obtained with two other approaches: amplitude spectra of Rayleigh wave and surface displacement from InSAR measurement. To analyze the cause of the event, coulomb failure stress change caused by the Wenchuan earthquake on the Longnan earthquake fault plane is calculated. The result shows that coulomb stress change is 30 kPa around the Longnan earthquake hypocenter, which exceeds the typical triggering threshold of 10 kPa. The research indicates that the Wenchuan earthquake probably promote the happening of the Longnan earthquake.
Key words:  Longnan earthquake  Source parameter  Rayleigh wave amplitude spectra  Surface displacement  Coulomb failure stress