本文選題：自發(fā)破裂 + 雙材料斷層��； 參考：《中國地震局地球物理研究所》2017年博士論文

【摘要】：地震是斷層的自發(fā)破裂動(dòng)力學(xué)過程。數(shù)值模擬斷層的自發(fā)破裂動(dòng)力學(xué)過程對于認(rèn)識地震的力學(xué)本質(zhì)、減輕地震災(zāi)害等有著重要的科學(xué)意義及應(yīng)用價(jià)值。本文首先對經(jīng)典的滑移弱化摩擦關(guān)系進(jìn)行了改進(jìn),然后對斷層的破裂過程進(jìn)行動(dòng)態(tài)數(shù)值模擬。模擬結(jié)果表明,利用改進(jìn)后的摩擦關(guān)系能夠產(chǎn)生脈沖型(pulse-like)破裂模式。斷層自發(fā)破裂過程受初始應(yīng)力場及摩擦關(guān)系影響,若初始應(yīng)力場中的剪應(yīng)力水平較低或滑移弱化摩擦本構(gòu)關(guān)系中的動(dòng)摩擦系數(shù)較大,則容易產(chǎn)生脈沖型破裂;反之,則容易產(chǎn)生裂紋型(crack-like)破裂。另外,為了研究雙材料(bimaterial)斷層破裂對強(qiáng)地面運(yùn)動(dòng)的影響,我們采用正則化的速率-狀態(tài)相關(guān)摩擦本構(gòu)關(guān)系計(jì)算了破裂沿著雙材料斷層傳播的二維有限元模型。模擬結(jié)果表明,雙材料機(jī)制對地震破裂過程以及斷層周邊區(qū)域的強(qiáng)地面運(yùn)動(dòng)有顯著影響。由斷層破裂輻射出的地震波導(dǎo)致的強(qiáng)地面運(yùn)動(dòng)在整個(gè)空間上的分布是不對稱的,其不對稱性會(huì)隨著斷層兩側(cè)材料差異程度的增加而增加。斷層破裂能否跨越斷層階區(qū)(stepover)繼續(xù)傳播,從而引發(fā)更大震級的地震,地震時(shí)斷層是否發(fā)生超剪切破裂導(dǎo)致地震災(zāi)害加劇,都是震源動(dòng)力學(xué)研究的重要內(nèi)容。本文利用有限單元方法模擬斷層階區(qū)對地震破裂傳播的控制作用以及對產(chǎn)生超剪切地震破裂的促進(jìn)作用。研究結(jié)果表明:斷層面上的摩擦系數(shù)減小、斷層周邊區(qū)域內(nèi)初始剪應(yīng)力增大以及較小的階區(qū)間距等,都將增加斷層破裂跳躍階區(qū)傳播的可能性;此外,這些物理因素都會(huì)對破裂的傳播速度產(chǎn)生影響。在一定條件下,破裂傳播速度會(huì)由在初始斷層上的亞剪切波速度,轉(zhuǎn)為在次級斷層上的超剪切波速度。結(jié)合以上在概念模型中對斷層自發(fā)破裂過程的模擬研究結(jié)果,我們根據(jù)汶川地震和玉樹地震發(fā)震斷層的實(shí)際幾何分別構(gòu)建有限單元數(shù)值模型,研究了汶川地震單側(cè)破裂過程的動(dòng)力學(xué)機(jī)制以及玉樹地震產(chǎn)生超剪切破裂過程的動(dòng)力學(xué)機(jī)制。2008年汶川大地震的破裂過程極其發(fā)雜,向東北方向的破裂距離長達(dá)300km,而向西南方向的破裂長度很小,呈現(xiàn)出單側(cè)破裂的主要特征。文中模擬并分析了汶川地震的破裂過程,結(jié)果表明:龍門山斷裂帶兩側(cè)的物性差異是造成汶川大地震單側(cè)傳播的決定性因素。由于2010年玉樹地震(Ms=7.1)產(chǎn)生了超剪切地震破裂,所以地震災(zāi)害特別嚴(yán)重。文中在模擬并分析玉樹地震的破裂過程后認(rèn)為:玉樹地震發(fā)震斷層走向與初始主應(yīng)力方向之間的關(guān)系斷層破裂由亞剪切轉(zhuǎn)化為超剪切破裂的可能原因。
[Abstract]:Earthquake is a dynamic process of spontaneous rupture of faults. Numerical simulation of the dynamic process of spontaneous rupture of faults has important scientific significance and application value in understanding the nature of earthquake mechanics and mitigating earthquake disasters. In this paper, the classical slip weakening friction relationship is improved firstly, and then the dynamic numerical simulation of the fracture process of the fault is carried out. The simulation results show that the pulse type (pulse-like) fracture mode can be generated by using the improved friction relationship. The spontaneous fracture process of a fault is affected by the initial stress field and the friction relationship. If the shear stress level in the initial stress field is lower or the dynamic friction coefficient in the sliding weakening friction constitutive relationship is large, the pulse rupture is easy to occur. The crack mode (crack-like) rupture is easy to occur. In addition, in order to study the effect of bimaterial (bimaterial) fault fracture on strong ground motion, we use regularized rate-state dependent friction constitutive relation to calculate the two-dimensional finite element model of fracture propagation along the bimaterial fault. The simulation results show that the bimaterial mechanism has a significant influence on the earthquake rupture process and the strong ground motion around the fault. The distribution of strong ground motion caused by seismic waves radiated by fault rupture is asymmetrical in the whole space, and the asymmetry will increase with the increase of material difference on both sides of the fault. Whether the fault rupture can continue to propagate across the fault order region, thus causing an earthquake with a larger magnitude, or whether the earthquake disaster is aggravated by the fault supershear rupture during the earthquake, is an important content of the focal dynamics research. In this paper, the finite element method is used to simulate the controlling effect of the fault order on the earthquake rupture propagation and the promoting effect on the supershear seismic rupture. The results show that the decrease of friction coefficient in fault plane, the increase of initial shear stress in the peripheral region of the fault, and the smaller interval between the steps will increase the probability of propagation of the fracture jump stage of the fault. These physical factors have an effect on the propagation speed of the rupture. Under certain conditions, the velocity of fracture propagation will change from the velocity of sub-shear wave on the initial fault to the velocity of the supershear wave on the secondary fault. Based on the simulation results of the spontaneous rupture process of the fault in the conceptual model above, a finite element numerical model is constructed according to the actual geometry of the Wenchuan earthquake and the Yushu earthquake. The dynamic mechanism of the unilateral rupture process of Wenchuan earthquake and the dynamic mechanism of the supershear rupture process of the Yushu earthquake are studied. The rupture process of the 2008 Wenchuan earthquake is extremely mixed. The rupture distance to northeast is 300km, while the length to southwest is very small, showing the main characteristics of unilateral rupture. The rupture process of Wenchuan earthquake is simulated and analyzed in this paper. The results show that the difference of physical properties on both sides of Longmenshan fault zone is the decisive factor for the unilateral propagation of Wenchuan earthquake. The earthquake disaster is especially serious because of the super shear earthquake rupture caused by the Yushu earthquake (Msl7. 1) in 2010. After simulating and analyzing the rupture process of the Yushu earthquake, it is concluded that the relationship between the strike of the earthquake generating fault and the direction of the initial principal stress of the Yushu earthquake may cause the transformation from sub-shear to super-shear fracture.
【學(xué)位授予單位】：中國地震局地球物理研究所
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：P315

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本文編號：2059089