本文選題：龍門山斷裂帶　切入點：震源機制　出處：《中國地震局地質研究所》2015年碩士論文　論文類型：學位論文

【摘要】：龍門山斷裂帶地處南北地震帶中段,介于青藏高原東緣巴顏喀拉與華南地塊四川盆地之間,是一條北東向斷裂帶。以映秀和北川附近為界,可將龍門山斷裂帶分為南、中、北3段(鄧起東等,1994；陳國光等,2007；徐錫偉等,2008)。2008年5月12日在龍門山斷裂帶中段發(fā)生了Mw7.9級汶川特大地震,造成巨大人員傷亡和經(jīng)濟損失。主震震源破裂過程研究(王衛(wèi)民等,2008；張勇等,2008)表明汶川地震是一次以逆沖為主兼具少量右旋走滑的事件。主要的動力來自巴顏喀拉塊體朝SEE方向的運動受到華南地塊阻擋而在龍門山斷裂帶的長期應力積累。龍門山斷裂帶能孕育出如此大的地震主要歸結于三大特征(Burchfiel et al.,2008；張培震等,2008；李延興等,2009；Zhang et al,2010),組成龍門山斷裂帶的是強度大的雜巖體,斷裂帶剖面為鏟型的構造結構,及整體處于低活動速率的閉鎖狀態(tài)下。地殼中應力主要受板塊運動、區(qū)域地質構造以及大地震觸發(fā)的應力變化影響,其自身也是地震直接動力源。對應力場及其時空演化特征的研究可幫助我們更好地理解區(qū)域構造變形。測量應力場的方法有很多,利用震源機制解反演應力場是現(xiàn)今研究應力場主要思路之一汶川地震發(fā)生后,在龍門山斷裂帶上產(chǎn)生了大量的余震。豐富的余震資料以及大尺度破裂帶的存在為研究龍門山斷裂帶動力學提供了重要數(shù)據(jù)基礎和模型參數(shù)。許多學者及機構基于汶川中強余震震源機制解獲得了應力場時空變化特征及蘊含的構造意義,這些結果提供了對龍門山斷裂帶構造應力場主要特征的認識,但由于現(xiàn)有研究主要針對4級以上的強余震,對局部應力場研究則稍顯不足。中強地震所需的驅動力數(shù)量級遠大于小震,這決定了其震源機制主要受區(qū)域構造應力的控制,對局部應力場變化不敏感。相對而言,小震不僅數(shù)量上占優(yōu),而且除受構造應力場影響外,還對大地震觸發(fā)的庫倫應力變化以及周邊斷層的影響敏感。小震的缺點在于信噪比低導致的有效觀測數(shù)據(jù)少,隨著近年來密集臺網(wǎng)的架設及區(qū)域精細速度結構的研究,小震定位結果及震源參數(shù)求解質量有了顯著提高。為了獲得龍門山斷裂帶中段應力場更精細的時空變化,本文利用川西流動地震臺陣記錄到的2007年1月至2008年10月間發(fā)生在龍門山斷裂帶中段的小震,通過P波初動極性結合SH/P振幅比反演計算震源機制解(Hardebeck and Shearer,2002：2003),并應用阻尼線性反演方法(Hardebeck and Michael,2006)對龍門山斷裂帶中段應力場進行反演,以便更好的了解龍門山斷裂帶中段應力場調整變化和遷移過程。研究結果表明：(1)汶川震前龍門山中段震源機制多為逆沖型且性質相似,表明區(qū)域應力場主要受構造應力的作用。應力場反演結果顯示S1近水平,方位為NWW-SEE,S3接近垂直,為逆沖型應力結構�；瑒于厔菅芯勘砻縻氪ǖ卣鹎皡^(qū)域應力場具有高度的一致性,區(qū)域已具備發(fā)生強震的動力條件。在汶川震中位置以南的寶興地區(qū)小震震源機制的P軸方向變?yōu)檠佚堥T山走向,表明其應力場在汶川起始破裂區(qū)以南存在異常變化,這與汶川地震、蘆山地震發(fā)生的關系尚需進一步研究。(2)對汶川小余震進行震源機制求解,發(fā)現(xiàn)震源機制以逆沖型為主,同時具有相當比例的正斷型地震。各類型比重隨時間變化明顯,逆沖型隨時間比例大幅上升,正斷及其他型比例下降。震源機制投影發(fā)現(xiàn)余震性質空間分布與斷層深部展布及區(qū)域速度結構具有相關性,時空形態(tài)揭示了局部應力場的復雜性。(3)應力張量反演結果顯示,震后初期小魚洞淺部地區(qū)受左旋走滑破裂影響,SH方位為NE-SW向,其他區(qū)域SH方位基本在EW和NWW-SEE范圍內,表明震后初期應力場主要受主震破裂傳播引起的動態(tài)應力影響。破裂傳播引起的動態(tài)應力使小震破裂面走向與傳播方向趨于一致,表現(xiàn)在SH方位趨向一致。隨著時間推移,應力場趨于平衡的過程中,深部應力結構由逆沖、走滑混合型向純逆沖型轉變,表明深部區(qū)域通過走滑來平衡破裂傳播造成的應力失穩(wěn),并向背景應力場轉變。淺部區(qū)域的應力調整追隨深部的變化特征,并有一定的滯后。(4)應力場反演揭示主震震中區(qū)深部SH方位模糊且為逆沖型應力結構,表明局部存在高強度的隆升凸起。先前發(fā)現(xiàn)的應力異�？赡軄碜杂�20km深度左右彭灌雜巖的隆升,雜巖體內NE側會出現(xiàn)由局部隆升導致的物質橫向變化,小魚洞-理縣走滑斷裂成因可能與之有關。本文對汶川地震前在整個龍門山地區(qū)、汶川地震后在龍門山中段發(fā)生的小震震源機制和應力場特征進行了研究,研究結果為汶川地震和蘆山地震孕育、發(fā)生的動力過程研究提供了新的證據(jù)和約束。
[Abstract]:The Longmen mountain fault zone is located in the middle of the North South seismic belt, between the eastern margin of the Qinghai Tibet Plateau and the Southern China block between the Sichuan basin, is a North East fault zone. In the vicinity of Yingxiu and Beichuan border, the Longmen mountain fault zone is divided into South, north, 3 (Deng Qidong, 1994; Chen Guoguang so, 2007; Xu Xiwei, 2008).2008 year in May 12th in the Longmen mountain fault zone occurred in the middle grade Mw7.9 Wenchuan earthquake caused huge casualties and economic losses. The rupture process of the mainshock hypocenter (Wang Weimin, 2008; Zhang Yong, 2008) show that the Wenchuan earthquake is a thrust with a small amount of. Dextral strike slip events. The main motion power from the Bayan Har block toward SEE is blocked in the Southern China block, Longmen Shan fault zone long-term stress accumulation. The Longmen mountain fault zone creates such a large earthquake is mainly due to the three characteristics (Bu Rchfiel et al., 2008; Zhang Peizhen, 2008; Li Yanxing, 2009; Zhang et al, 2010), consisting of the Longmen Shan fault zone is the complex rock strength, structural fracture zone profile for shovel type, and the whole is closed when the low activity rate. Under stress to plate by the movement of the earth crust in effect, the regional geological structure and earthquake triggering stress changes, its seismic direct power source. The stress field and its temporal evolution characteristics can help us better understand the regional tectonic deformation. There are many methods of measurement should be stress field, using the focal mechanism solutions of stress field inversion is now on stress one of the main ideas of the Wenchuan earthquake field, in the Longmen mountain fault zone had a large number of aftershocks. Rupture of the aftershock data rich and large scale belt has provided important data base for the study of the Longmen Mountain Fault Zone dynamics The foundation and the parameters of the model. Many scholars and institutions of solutions for the stress field contains the spatial and temporal variation characteristics and tectonic significance of the focal mechanism of strong aftershocks in Wenchuan based on these results provide understanding of the fracture zone of Longmen mountain tectonic stress field characteristics, but because of the existing literatures mainly focus on strong aftershock of more than 4, the local the study of stress field is slightly insufficient. The driving force required strong earthquake magnitude greater than a small earthquake, which determines its focal mechanism is mainly controlled by regional tectonic stress, is not sensitive to the changes of local stress field. In contrast, the number of small earthquakes is not only the dominant, but also affected by tectonic stress field effects, also on the earthquake triggered Kulun effect of stress changes and faults. The disadvantage is that the small earthquake sensitive effective observation data with low signal-to-noise ratio leads to less, with the erection and fine velocity structure of network intensive in recent years. The research results of small earthquake location and source parameters for quality has been significantly improved. In order to stress the finer temporal and spatial variation of middle Longmen mountain fault belt has received, the Sichuan Mobile seismic array recorded from January 2007 to October 2008 occurred in the small earthquake belt in the section of the Longmen mountain fault, the first motion of P wave polar ratio inversion calculation of focal mechanism solutions combined with the amplitude of SH/P (Hardebeck and Shearer, 2002:2003), and the application of damped linear inversion method (Hardebeck and Michael, 2006) of the Longmen Mountain Fault Zone Middle stress field inversion, in order to better understand the Longmen Mountain Fault Zone of stress field change and migration process. The results of the study show that: (1) Wen Chuanzhen before the middle section of Longmen mountain is the focal mechanism of thrust type and properties similar to that of regional stress field is mainly affected by tectonic stress. Stress field inversion results show that the S1 horizontal side For NWW-SEE S3, close to the vertical stress, structure of thrust type. Study on sliding trend shows that before the Wenchuan earthquake the regional stress field has a high degree of consistency, area has dynamic conditions of strong earthquake epicenter in Wenchuan. Position in the P axis direction of focal mechanism of small earthquakes in Baoxing area south of the direction along the Longmen that mountain, the stress field in the Wenchuan area to the south of the initial rupture abnormal changes, the Wenchuan earthquake and the Lushan earthquake, the relationship is in need of further research. (2) the focal mechanism solution of small aftershocks were found in Wenchuan, the focal mechanism of thrust type earthquakes are broken, and has a considerable proportion. The proportion of each type changed over time, thrust type with a substantial increase in the proportion of normal fault and other types decreased. The focal mechanism that aftershock spatial distribution and projection properties of deep faults and regional distribution of velocity structure has a correlation, when The empty form revealed the complexity of stress field. (3) stress tensor inversion results show that the Xiaoyudong shallow areas after the earthquake early by sinistral strike slip rupture, SH range is NE-SW to other areas of SH in EW and NWW-SEE basic range range, showed that the initial period after the earthquake stress field to dynamic shock rupture propagation caused by stress effects. The dynamic stress caused by the rupture of small earthquakes rupture direction and propagation direction are consistent, consistent performance in SH range. With the passage of time, the process of stress field tends to balance in the deep stress structure composed of thrust, strike slip hybrid to pure thrust the transformation that through deep regional strike slip rupture propagation to balance the stress caused by the instability, and the stress field change to the background of force adjustment. Follow the deep shallow region, and there is a certain lag. (4) the stress field inversion reveal the main deep earthquake epicenter area SH range and fuzzy thrust type stress structure, show that the local existence of high strength uplift raised. Previously discovered abnormal stress may come from a depth of about 20km the PENGGUAN complex uplift, complex NE in the rock side will appear by the local uplift and lateral variation of material lead, Xiaoyudong Lixian the strike slip fault causes may be related to this paper. Before the Wenchuan earthquake in the Longmen mountain area, Wenchuan after the earthquake in the Longmen mountains of small earthquake focal mechanism and stress field characteristics were studied, the results for the Wenchuan earthquake and the Lushan earthquake, the dynamic force provides new evidence and constraints study.

【學位授予單位】：中國地震局地質研究所
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：P315.2

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