利用背景噪声数据研究芦山地震震源区介质速度变化

发布时间：2018-05-29 05:20

  本文选题：背景噪声 + 芦山地震　； 参考：《中国地震局地震预测研究所》2015年硕士论文

【摘要】：2013年4月20日在龙门山断裂带南段芦山地区发生了Ms7.0级地震,此次地震是继2008年5月12日汶川Ms8.0级地震后又一次发生在龙门山断裂带上的破坏性地震。在这两次地震的破裂区及余震区之间存在一个空段,有再次发生强震的可能性。本论文的研究目标即是利用芦山地震震中周围地震台站的观测数据,监测芦山地震震源震区在地震发生前、地震发生后是否存在介质性质的变化,以及上述空段区能否观测到介质性质的异常变化信息。本论文利用背景噪声数据提取出经验格林函数的方法,获得了芦山地震震源区地下介质的速度时间变化过程。本研究中我们使用芦山地震震源区附近的9个台站记录到的背景噪声数据的垂直分量,并将这9个台站组成14条不同的路径,而这些路径覆盖了芦山地震的震源区以及上述空段区。我们研究的时间段范围是从2012年1月到2014年10月,共34个月。首先将原始数据重新采样至20Hz。经过对数据的多次试验后发现,10s～20s周期的经验格林函数在地震前后相似度较高,并且也较为稳定可靠,因此对观测数据滤波到10s～20s的频带,使用滑动绝对平均方法对其进行归一化处理,再经过白化处理后,通过计算出一条路径上的两个台站之间的互相关,分别提取出参考经验格林函数和单天实际经验格林函数,最后利用移动窗口互相关谱的方法计算出了选择出的这14条路径上地震波速度的时间变化。论文研究结果表明,在芦山地震发生前,覆盖震源区的所有路径上未能观测到速度变化,该结果与国内外使用同样方法对6级以上构造地震的震例研究结果一致。而穿过震源区的部分台站对路径,在地震发生后存在速度的快速减小,量级为0.4%,且持续2个月该变化消失。其中,穿过芦山地震和汶川地震两次地震的余震之间“空段”的几条路径在地震后没有发现有明显的速度变化。由于此次芦山地震的震级相比于汶川地震的震级不大,破裂范围小,同震位移及分布范围小,因此在震源区只有少数的台站对发现有速度变化。另一方面,使用10s～20s周期范围的面波反应了较大范围和深度的介质性质。因此震后的介质变化过程如果较为细微,则也有可能被掩盖。
[Abstract]:On April 20, 2013, a Ms7.0 earthquake occurred in the Lushan area of the southern section of the Longmenshan fault zone. This earthquake is another destructive earthquake that occurred on the Longmenshan fault zone after the Wenchuan earthquake of magnitude Ms8.0 on May 12, 2008. There is a gap between the rupture zone and the aftershock area of the two earthquakes, and it is possible that strong earthquakes will occur again. The purpose of this paper is to monitor whether there is a change in the properties of the Lushan earthquake before and after the Lushan earthquake, using the observation data of the seismic station around the epicenter of the Lushan earthquake. And whether the abnormal variation information of medium properties can be observed in the above space region. In this paper, the empirical Green's function is extracted from the background noise data, and the velocity and time variation process of the underground media in the focal area of the Lushan earthquake is obtained. In this study, we use the vertical component of background noise data recorded by 9 stations near the focal area of the Lushan earthquake, and form 14 different paths from these 9 stations. These paths cover the focal area of the Lushan earthquake and the above-mentioned empty section. We studied a period of 34 months from January 2012 to October 2014. First, the raw data is resampled to 20Hz. After many experiments on the data, it is found that the empirical Green's function of 10 s ~ 20 s period has a high similarity before and after the earthquake, and is also more stable and reliable. Therefore, the observed data is filtered into the frequency band of 10s~20s. The sliding absolute average method is used to normalize it. After whitening, the cross-correlation between the two stations on a path is calculated, and the reference empirical Green's function and the single day practical empirical Green's function are extracted, respectively. Finally, the time variation of seismic wave velocity on these 14 paths is calculated by using the method of cross-correlation spectrum of moving window. Before the Lushan earthquake occurred, no velocity change could be observed in all the paths covering the focal area, which is consistent with the results of the case study of earthquakes with M 鈮，

本文编号：1949648