本文選題：背景噪聲 + 蘆山地震　； 參考：《中國(guó)地震局地震預(yù)測(cè)研究所》2015年碩士論文

【摘要】：2013年4月20日在龍門(mén)山斷裂帶南段蘆山地區(qū)發(fā)生了Ms7.0級(jí)地震,此次地震是繼2008年5月12日汶川Ms8.0級(jí)地震后又一次發(fā)生在龍門(mén)山斷裂帶上的破壞性地震。在這兩次地震的破裂區(qū)及余震區(qū)之間存在一個(gè)空段,有再次發(fā)生強(qiáng)震的可能性。本論文的研究目標(biāo)即是利用蘆山地震震中周?chē)卣鹋_(tái)站的觀測(cè)數(shù)據(jù),監(jiān)測(cè)蘆山地震震源震區(qū)在地震發(fā)生前、地震發(fā)生后是否存在介質(zhì)性質(zhì)的變化,以及上述空段區(qū)能否觀測(cè)到介質(zhì)性質(zhì)的異常變化信息。本論文利用背景噪聲數(shù)據(jù)提取出經(jīng)驗(yàn)格林函數(shù)的方法,獲得了蘆山地震震源區(qū)地下介質(zhì)的速度時(shí)間變化過(guò)程。本研究中我們使用蘆山地震震源區(qū)附近的9個(gè)臺(tái)站記錄到的背景噪聲數(shù)據(jù)的垂直分量,并將這9個(gè)臺(tái)站組成14條不同的路徑,而這些路徑覆蓋了蘆山地震的震源區(qū)以及上述空段區(qū)。我們研究的時(shí)間段范圍是從2012年1月到2014年10月,共34個(gè)月。首先將原始數(shù)據(jù)重新采樣至20Hz。經(jīng)過(guò)對(duì)數(shù)據(jù)的多次試驗(yàn)后發(fā)現(xiàn),10s～20s周期的經(jīng)驗(yàn)格林函數(shù)在地震前后相似度較高,并且也較為穩(wěn)定可靠,因此對(duì)觀測(cè)數(shù)據(jù)濾波到10s～20s的頻帶,使用滑動(dòng)絕對(duì)平均方法對(duì)其進(jìn)行歸一化處理,再經(jīng)過(guò)白化處理后,通過(guò)計(jì)算出一條路徑上的兩個(gè)臺(tái)站之間的互相關(guān),分別提取出參考經(jīng)驗(yàn)格林函數(shù)和單天實(shí)際經(jīng)驗(yàn)格林函數(shù),最后利用移動(dòng)窗口互相關(guān)譜的方法計(jì)算出了選擇出的這14條路徑上地震波速度的時(shí)間變化。論文研究結(jié)果表明,在蘆山地震發(fā)生前,覆蓋震源區(qū)的所有路徑上未能觀測(cè)到速度變化,該結(jié)果與國(guó)內(nèi)外使用同樣方法對(duì)6級(jí)以上構(gòu)造地震的震例研究結(jié)果一致。而穿過(guò)震源區(qū)的部分臺(tái)站對(duì)路徑,在地震發(fā)生后存在速度的快速減小,量級(jí)為0.4%,且持續(xù)2個(gè)月該變化消失。其中,穿過(guò)蘆山地震和汶川地震兩次地震的余震之間“空段”的幾條路徑在地震后沒(méi)有發(fā)現(xiàn)有明顯的速度變化。由于此次蘆山地震的震級(jí)相比于汶川地震的震級(jí)不大,破裂范圍小,同震位移及分布范圍小,因此在震源區(qū)只有少數(shù)的臺(tái)站對(duì)發(fā)現(xiàn)有速度變化。另一方面,使用10s～20s周期范圍的面波反應(yīng)了較大范圍和深度的介質(zhì)性質(zhì)。因此震后的介質(zhì)變化過(guò)程如果較為細(xì)微,則也有可能被掩蓋。
[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，

本文編號(hào)：1949648