本文選題：汶川地震 + 蘆山地震��； 參考：《中國地震局地震預(yù)測研究所》2015年碩士論文

【摘要】：2013年4月20日,位于龍門山斷裂帶南段,雅安市蘆山縣發(fā)生Ms 7.0地震。由于震級較大,地震發(fā)生區(qū)域地質(zhì)條件復(fù)雜,并且與龍門山斷裂帶中北段發(fā)生的汶川地震在時(shí)間和空間上相近,因二者之間可能的關(guān)聯(lián)性,分析蘆山地震震前地殼形變狀態(tài)并與汶川地震震后應(yīng)力變化進(jìn)行對比就顯得十分必要。另一方面,蘆山地震發(fā)震斷層未破裂到地表,不同研究者給出破裂方式的不同,更需要進(jìn)一步分析蘆山地震的同震滑動分布并深究其內(nèi)在原因。本文以蘆山地震為研究對象,以不同時(shí)段的GPS速度場數(shù)據(jù)和蘆山地震同震位移數(shù)據(jù)為約束,對蘆山地震震前的應(yīng)力應(yīng)變變化及同震位錯(cuò)進(jìn)行相關(guān)研究,主要內(nèi)容如下:1.基于1999~2007時(shí)段和2009~2013時(shí)段GPS速度場數(shù)據(jù),討論了蘆山地震震前龍門山斷裂帶附近區(qū)域的應(yīng)變變化及其與應(yīng)力的關(guān)系通過最小二乘配置方法,計(jì)算龍門山斷裂帶附近面應(yīng)變率及主應(yīng)變。結(jié)果顯示,汶川地震前龍門山斷裂帶中北段應(yīng)變積累率接近于0,表明這一地區(qū)應(yīng)變積累達(dá)到極限,當(dāng)巴顏喀拉塊體繼續(xù)推擠時(shí),中北段相對南段更容易發(fā)生破裂;汶川地震后南段仍處于斷層閉鎖狀態(tài),并且應(yīng)變積累率增加,使得該地區(qū)地震危險(xiǎn)性增強(qiáng);汶川地震前主應(yīng)變主要集中在鮮水河斷裂帶,且對其產(chǎn)生左旋變形背景;利用半無限空間位錯(cuò)程序計(jì)算汶川地震震后余滑與粘滑造成的主應(yīng)力變化,與GPS所計(jì)算主應(yīng)變進(jìn)行對比。結(jié)果顯示,汶川地震后巴顏喀拉塊體南側(cè)主應(yīng)變的減小與北側(cè)主應(yīng)變的增大主要受汶川地震震后效應(yīng)的影響;蘆山震源區(qū)主應(yīng)變的變化主要受區(qū)域構(gòu)造的影響;川滇地塊受汶川地震震后影響不顯著。2、以蘆山地震同震位移數(shù)據(jù)為約束,反演蘆山地震同震滑動分布,并分析蘆山地震左旋破裂方式產(chǎn)生的原因。在前人研究的基礎(chǔ)上,對斷層模型采用接近實(shí)際的曲面斷層設(shè)定,斷層傾角隨深度均勻變化,并用指數(shù)函數(shù)模擬斷層的幾何特征�？紤]發(fā)震斷層未破裂到地表特點(diǎn)及地球的分層情況,以蘆山地震同震位移為約束,采用SBIF反演方法反演得到蘆山地震同震滑動分布。利用最小二乘配置方法分析汶川地震前后蘆山地震震源區(qū)域主壓應(yīng)變方向角的變化,以加深對蘆山地震左旋破裂方式產(chǎn)生原因的理解。結(jié)果顯示,蘆山地震破裂以逆沖為主兼有左旋走滑特征;左旋特征在斷層南部更為明顯,滑動角隨斷層深度的增加而減小;將同震位移的模型值與GPS觀測值進(jìn)行對比,兩者擬合效果較好,改正了平面斷層設(shè)定下LS06點(diǎn)位垂向誤差較大的情況;汶川地震后,由于龍門山斷裂帶中北段斷層解鎖,背景場發(fā)生變化,使得蘆山地震震源區(qū)域主壓應(yīng)變方向角發(fā)生順時(shí)針旋轉(zhuǎn),表明龍門山斷裂帶南段長期積累的背景場對蘆山地震發(fā)震斷層施加了左旋走滑作用。
[Abstract]:On April 20, 2013, Ms 7.0 earthquake occurred in Lushan County, Ya'an City. Because of its large magnitude and complex regional geological conditions, it is similar to the Wenchuan earthquake in time and space in the middle and north segment of the Longmenshan fault zone, because of the possible correlation between the two. It is necessary to analyze the crustal deformation state before the Lushan earthquake and compare it with the post-Wenchuan earthquake stress change. On the other hand, the Lushan seismogenic fault did not break to the surface of the earth. Different researchers have given different rupture modes, so it is necessary to further analyze the coearthquake slip distribution of the Lushan earthquake and study its internal reasons. Taking the Lushan earthquake as the research object and taking the GPS velocity field data and the coseismic displacement data of the Lushan earthquake at different periods as constraints, this paper studies the stress-strain changes and coseismic dislocations before the Lushan earthquake. The main contents are as follows: 1. Based on the GPS velocity field data from 1999 to 2007 and 2009 to 2013, the strain variation and the relationship between strain and stress in the Longmenshan fault zone before the Lushan earthquake are discussed by the least square collocation method. The surface strain rate and principal strain around the Longmenshan fault zone are calculated. The results show that the strain accumulation rate of the central and northern segment of the Longmenshan fault zone is close to zero before the Wenchuan earthquake, which indicates that the strain accumulation in this area has reached the limit, and when the Bayan Kara block continues to push, the central and northern segment is more prone to rupture than the south segment. After the Wenchuan earthquake, the south segment is still in the state of fault closure and the strain accumulation rate increases, which makes the seismic risk increase in this area, the main strain before the Wenchuan earthquake is mainly concentrated in the Xianshuihe fault zone, and the left-handed deformation background is produced. The variation of principal stress caused by afterslip and stick-slip after Wenchuan earthquake is calculated by using semi-infinite space dislocation program, which is compared with the principal strain calculated by GPS. The results show that the decrease of the main strain in the south side of Bayan Kara block and the increase of the main strain in the north side after the Wenchuan earthquake are mainly affected by the post-earthquake effect of Wenchuan earthquake, and the variation of the main strain in the focal area of Lushan earthquake is mainly affected by the regional tectonics. The Sichuan-Yunnan block is not significantly affected by Wenchuan earthquake. Taking the Lushan earthquake coseismic displacement data as the constraint, the distribution of the Lushan earthquake co-seismic slip is inversed, and the causes of the Lushan earthquake left-lateral rupture mode are analyzed. On the basis of previous research, the fault model is set up with curved surface fault, the dip angle of fault varies uniformly with depth, and the geometric characteristics of fault are simulated by exponential function. Considering the characteristics of unruptured fault to the surface of the earth and the stratification of the earth, the coseismic slip distribution of the Lushan earthquake is obtained by using SBIF inversion method, which is constrained by the Lushan earthquake coseismic displacement. The change of principal compressive strain direction angle of Lushan earthquake focal area before and after Wenchuan earthquake was analyzed by using least square collocation method in order to understand the cause of Lushan earthquake left-lateral rupture mode. The results show that the Lushan earthquake rupture mainly consists of thrust and left-lateral strike-slip, the left-lateral feature is more obvious in the southern part of the fault, and the slip angle decreases with the increase of fault depth, and the model values of co-seismic displacement are compared with the observed values of GPS. After Wenchuan earthquake, the background field changed due to the fault unlocking in the middle and north segment of Longmenshan fault zone, the vertical error of LS06 point was larger than that of LS06 point under the setting of plane fault, after the Wenchuan earthquake, the background field changed because of the fault unlocking in the middle and north segment of Longmenshan fault zone. The rotation of the principal compressive strain direction angle in the focal area of the Lushan earthquake occurs clockwise, which indicates that the long-accumulated background field in the southern segment of the Longmenshan fault zone exerts a left-lateral strike-slip effect on the Lushan earthquake generating fault.
【學(xué)位授予單位】：中國地震局地震預(yù)測研究所
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：P315.727

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