本文選題：地震走時反演　切入點：算法試驗　出處：《中國地震局地球物理研究所》2017年碩士論文

【摘要】：本文詳細研究了Zelt和Smith在1992年提出的射線反演Rayinvr算法。模型參數(shù)化靈活設(shè)置速度和界面節(jié)點的個數(shù)和位置,使不規(guī)則四邊形網(wǎng)格大小的劃分與地下介質(zhì)被數(shù)據(jù)分辨的狀況相一致,很大程度上避免了過參數(shù)化引起的反演假象和欠參數(shù)化引起的不能分辨細結(jié)構(gòu)的缺陷。層邊界光滑技術(shù)的應(yīng)用避免了模型參數(shù)化邊界轉(zhuǎn)折點造成的人為的射線聚焦和焦散,進而在地表接收點引起非客觀的地震射線影區(qū)和三重震相的現(xiàn)象。四邊形內(nèi)速度采用雙線性內(nèi)插,使得內(nèi)部射線追蹤存在解析解。到達觀測點的射線追蹤采用試射法,大大提高了算法的效率。反演使用阻尼最小二乘算法,提高了算法的穩(wěn)定性。結(jié)果在追蹤到射線數(shù)、走時殘差和阻尼因子之間取折中。對影響該算法的因素:阻尼因子選取、初始模型選取、走時隨機擾動和數(shù)據(jù)不確定性進行了試驗,測試了多種因素對反演的影響。阻尼因子是影響算法效率和結(jié)果分辨率的關(guān)鍵因素。在實際資料處理過程中,取大的阻尼值將使反演迭代加長,降低算法的效率,而且大大降低了結(jié)果分辨率;阻尼值取的較小,可能使反演無法進行。為了提高計算效率和得到分辨較佳的最終結(jié)果,在每次迭代時都需要嘗試不同的阻尼值,這是非常耗時間的。對此,我們對阻尼因子選取進行改進,并做了測試試驗。我們做法是在初始迭代中給阻尼因子賦一個比較大的值,以后在迭代的每一步中通過給該值乘以一個小于1的數(shù),逐漸減小阻尼因子,增大收斂速度和提高模型參數(shù)分辨率。測試表明,完成反演只需幾次選取這個小于1的乘子就可以了。這種改進大大提高了計算效率。Rayinvr地震走時反演算法是一種線性化反演算法,從十分不同的初始模型開始反演有可能收斂次級極值點,搜索不到全局最優(yōu)解。對此,我們進行了另外兩個試驗,以獲得算法對觀測數(shù)據(jù)不確定性和不同的初始模型的敏感程度。結(jié)果表明,在對初始模型選取時應(yīng)盡可能的使用先驗信息,能有效地避免反演不能進行和追蹤到的射線數(shù)過少等問題;而觀測數(shù)據(jù)的獲取也應(yīng)該盡量準(zhǔn)確。通過對鎮(zhèn)康-瀘西人工地震剖面的資料處理,重建了滇南中部高分辨的二維地殼上地幔速度結(jié)構(gòu)。反演中使用參數(shù)和初始模型基于試驗內(nèi)容進行選取,結(jié)果與正演相比有所改善。地殼結(jié)構(gòu)主要以沉積層、C1、C2、C3、莫霍面分層,每層都出現(xiàn)了明顯的橫向速度不均勻性,以樁號400km處紅河斷裂帶為界,西側(cè)速度偏低,而東側(cè)速度偏高,莫霍面深度明顯增厚。在小江斷裂帶出現(xiàn)明顯低速,往東進入華南大陸為穩(wěn)定陸塊。
[Abstract]:In this paper, the authors study in detail the ray inversion Rayinvr algorithm proposed by Zelt and Smith in 1992. The model is parameterized to set the velocity and the number and position of interface nodes. The partition of irregular quadrilateral mesh size is consistent with the resolution of underground media by data. To a great extent, the defects of inversion illusion caused by over-parameterization and indiscernibility of fine structure caused by under-parameterization are avoided. The application of layer boundary smoothing technique avoids the artificial ray focusing and defocusing caused by the turning point of model parameterized boundary. The velocity in the quadrilateral is bilinear interpolated so that there is an analytical solution to the internal ray tracing. The ray tracing to the observation point is carried out by test shooting method, which leads to the phenomenon of non-objective seismic ray area and triple seismic phase at the receiving point of the earth's surface, and the velocity of the quadrilateral is bilinear interpolated. The efficiency of the algorithm is greatly improved. The stability of the algorithm is improved by using the damped least square algorithm. Results the tradeoff between tracing the number of rays, the travel time residuals and the damping factor is taken. The selection of initial model, the random disturbance of travel time and the uncertainty of data are tested, and the influence of many factors on inversion is tested. Damping factor is the key factor to affect the efficiency and resolution of the algorithm. Taking a large damping value will make the inversion iteration longer, reduce the efficiency of the algorithm, and greatly reduce the resolution of the result. A smaller damping value may make the inversion impossible. In order to improve the computational efficiency and obtain a better resolution of the final results, We need to try different damping values at each iteration, which is very time-consuming. For this, we improve the damping factor selection and do a test experiment. We assign a larger value to the damping factor in the initial iteration. In each step of the iteration, by multiplying the value by a number less than 1, the damping factor is gradually reduced, the convergence rate is increased and the resolution of the model parameters is improved. It takes only a few times to select the multiplier less than 1 to complete the inversion. This improvement greatly improves the calculation efficiency. Rayinvr seismic walk time inversion algorithm is a linearized inversion algorithm. From the very different initial model, the possible convergence of the secondary extremum point is inversed, and the global optimal solution can not be found. In this case, we have carried out two other experiments. In order to obtain the sensitivity of the algorithm to the uncertainty of observation data and the different initial models, the results show that priori information should be used as far as possible in selecting the initial model. It can effectively avoid the problem that the inversion can not be carried out and the number of rays that can be traced is too small, and the acquisition of observation data should be as accurate as possible. By processing the data of Zhenkang Luxi artificial seismic profile, The high resolution 2-D crust and upper mantle velocity structure in the central part of southern Yunnan was reconstructed. The parameters and initial model were selected based on the experimental contents in the inversion, and the results were improved compared with the forward model. The crustal structure was mainly composed of sedimentary layer C _ (1) C _ (2) C _ (2) and Moho stratification. There is obvious lateral velocity inhomogeneity in each layer, with the Honghe fault zone at pile number 400km as the boundary, the velocity on the west side is low, and the velocity on the east side is on the high side, and the Moho depth is obviously thickened, and in the Xiaojiang fault zone there is an obvious low velocity. Eastward access to the South China continent is a stable continent.
【學(xué)位授予單位】：中國地震局地球物理研究所
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：P631.4

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