本文選題：有限元數(shù)值模擬 + 特征地震�。� 參考：《中國(guó)科學(xué)技術(shù)大學(xué)》2015年博士論文

【摘要】：彈性回跳理論目前被認(rèn)為是構(gòu)造地震發(fā)生的主要機(jī)制。所謂的彈性回跳理論是：斷層兩邊巖石在構(gòu)造應(yīng)力的作用下發(fā)生形變,應(yīng)力和應(yīng)變能逐漸累積,當(dāng)應(yīng)力達(dá)到一定程度就會(huì)造成斷層的突然活動(dòng),導(dǎo)致地震發(fā)生,應(yīng)變能也得到突然釋放。野外地質(zhì)調(diào)查和巖石物理實(shí)驗(yàn)都顯示,地震的這種過程可以簡(jiǎn)化為斷層的粘滑行為。而且斷層的這種粘滑可以用滑移弱化摩擦準(zhǔn)則或一個(gè)與速率和狀態(tài)相關(guān)的摩擦準(zhǔn)則來表示。研究也發(fā)現(xiàn),地震發(fā)生時(shí),斷層面的破裂速度可能會(huì)出現(xiàn)超剪切現(xiàn)象。而超剪切破裂可能會(huì)在水平方向上產(chǎn)生擴(kuò)張的平面S波以及馬赫波,這些波會(huì)顯著地加強(qiáng)斷層破裂方向上的地面震動(dòng)以及破壞力,即有著更強(qiáng)的能量輻射。地震斷層的粘滑行為以及斷層面的破裂過程與周圍地質(zhì)環(huán)境密切相關(guān),如斷層的應(yīng)力擾動(dòng)或孔隙壓變化可能會(huì)影響地震的周期以及地震的大小(長(zhǎng)時(shí)間尺度,年)、也有可能阻礙斷層的破裂或觸發(fā)超剪切破裂(短時(shí)間尺度,秒)。深刻認(rèn)識(shí)周圍環(huán)境變化對(duì)斷層滑動(dòng)和破裂過程的影響,對(duì)進(jìn)一步理解地震的物理過程以及防震減災(zāi)工作都具有重要的理論和現(xiàn)實(shí)意義。本文意欲通過建立物理模型的方法,研究周圍環(huán)境應(yīng)力變化對(duì)斷層粘滑行為以及斷層面的破裂過程的影響。具體來說,就是利用有限元方法以及滑移弱化摩擦準(zhǔn)則,通過模擬斷層應(yīng)力加載的過程來認(rèn)識(shí)斷層的滑動(dòng)規(guī)律、并探索斷層的動(dòng)態(tài)破裂過程,以期能加深對(duì)地震物理過程的理解,并為防震減災(zāi)提供一些有價(jià)值的科學(xué)依據(jù)。首先,建立一個(gè)二維走滑斷層數(shù)值模型,并結(jié)合斷層滑移弱化摩擦準(zhǔn)則對(duì)斷層長(zhǎng)期滑動(dòng)規(guī)律以及應(yīng)力擾動(dòng)對(duì)其影響進(jìn)行了研究；然后,以日本2011年Tohoku Mw9.0地震為具體實(shí)例,建立一個(gè)二維曲線斷層數(shù)值模型,并且利用高精度的形變觀測(cè)來約束模型；最后,在二維平面走滑斷層中,研究局部有效正應(yīng)力增加的障礙體(barrier)對(duì)超剪切破裂的觸發(fā)作用。主要結(jié)果如下：(1)數(shù)值計(jì)算結(jié)果表明,在均勻應(yīng)力分布情況下,平面斷層滑動(dòng)顯示出典型的特征地震規(guī)律,斷層面上的應(yīng)力擾動(dòng)對(duì)斷層滑動(dòng)規(guī)律產(chǎn)生影響,壓應(yīng)力增加明顯延遲地震的發(fā)生時(shí)間,并增加地震釋放的能量。應(yīng)力擾動(dòng)發(fā)生在地震破裂臨界區(qū)時(shí)的影響比在震前滑移區(qū)時(shí)的影響顯著。當(dāng)發(fā)生在地震滑移區(qū)時(shí),若應(yīng)力擾動(dòng)足夠大,則壓應(yīng)力增大會(huì)造成地震發(fā)生時(shí)部分動(dòng)力斷層被暫時(shí)鎖住,使得地震釋放的能量變小,但可增加后續(xù)地震的能量；而壓應(yīng)力減小則可導(dǎo)致地震規(guī)律產(chǎn)生更加復(fù)雜的變化,會(huì)即時(shí)觸發(fā)地震。如果應(yīng)力擾動(dòng)發(fā)生在一個(gè)地震周期的早期,則觸發(fā)的地震較小,但可導(dǎo)致隨后的地震提前發(fā)生；如果應(yīng)力擾動(dòng)發(fā)生在一個(gè)地震周期的后期,則會(huì)觸發(fā)大地震。當(dāng)應(yīng)力擾動(dòng)位于震前滑移區(qū)或破裂臨界區(qū)時(shí),小的擾動(dòng)也可能產(chǎn)生類似的效果。應(yīng)力擾動(dòng)產(chǎn)生越晚,這種影響也越明顯。應(yīng)力擾動(dòng)發(fā)生在破裂臨界區(qū)的影響最明顯。應(yīng)力擾動(dòng)的影響一般主要集中在應(yīng)力發(fā)生擾動(dòng)后的1-2個(gè)地震周期內(nèi)。后續(xù)地震基本恢復(fù)無應(yīng)力擾動(dòng)時(shí)的特征地震規(guī)律。(2)數(shù)值模擬計(jì)算結(jié)果顯示,模型在1000年間的6次大地震表現(xiàn)出特征重復(fù)地震的規(guī)律。模型的數(shù)值結(jié)果與地表同震GPS位移、震間GPS速度分布都具有較好的一致性。此外,模型結(jié)果也顯示了在兩次大地震中間會(huì)發(fā)生一次小地震。其中大地震的重復(fù)周期約為161年、單位破裂長(zhǎng)度地震大小約為1.13 x 1020N m/km、小地震的地震矩約為5.62×1018Nm/km.進(jìn)一步的計(jì)算結(jié)果表明,模型地幔楔的巖石圈和軟流圈的粘性大小對(duì)震間GPS速度場(chǎng)產(chǎn)生顯著影響。地幔楔的巖石圈和軟流圈的粘性存在參數(shù)折中。如果軟流圈粘性從1020 Pa s減小為2.5×1019 Pa s,為得到與觀測(cè)基本相符的震間GPS速度分布,模型地幔楔巖石圈的粘性需從1020 Pa s增加到2.5×1020 Pa s。數(shù)值計(jì)算也顯示,在一個(gè)地震周期內(nèi),模型空間重力變化值和地面點(diǎn)重力變化值基本上隨時(shí)間均勻變化,在大陸一側(cè)距海溝100km處分別可達(dá)-366 μgal和667μgal,但在陸地上變化較小,最大變化處約距海溝200 km,變化數(shù)值約為159 μgal和-77μgal;速度場(chǎng)的變化主要發(fā)生在震后約5年的時(shí)間內(nèi),此后基本保持穩(wěn)定增加。(3)模擬結(jié)果證實(shí),障礙體不僅會(huì)減緩或者阻止地震破裂的傳播,但是同樣也可能觸發(fā)超剪切破裂。研究結(jié)果表明,超剪切破裂出現(xiàn)在一個(gè)參數(shù)區(qū)域內(nèi),這個(gè)區(qū)域介于兩條直線邊界之間。而如果障礙體的寬度位于下邊界的下方,那么地震破裂能夠克服這個(gè)障礙體,并且保持亞剪切破裂速度傳播。如果障礙體的寬度位于上邊界的上方,則障礙體始終能夠阻止地震破裂的傳播。此外,本文結(jié)果還表明,這種由障礙體觸發(fā)產(chǎn)生的超剪切破裂傳播可能最終會(huì)減速至亞剪切,這個(gè)過程依賴于障礙體的寬度以及位置。隨著障礙體的寬度從下邊界增加至上邊界,障礙體導(dǎo)致的主破裂速度減量逐漸增加,并且超剪切破裂傳播持續(xù)的距離也隨之增加。這些結(jié)果表明斷層上的障礙體可能并沒有阻止地震破裂傳播,反而可能觸發(fā)超剪切破裂轉(zhuǎn)變。而這種超剪切破裂轉(zhuǎn)變對(duì)于近場(chǎng)強(qiáng)地面運(yùn)動(dòng)以及地震破壞力具有非常重要的影響。
[Abstract]:Elastic rebound theory is considered to be the main mechanism of tectonic earthquake. The so-called elastic rebound theory is that the rock on both sides of the fault is deformed under the action of tectonic stress, and the stress and strain can accumulate gradually. When the stress reaches a certain extent, the sudden movement of the fault leads to the occurrence of the earthquake, and the strain energy can also be suddenly released. Field geological survey and rock physics experiments have shown that this process can be simplified as a slip of the fault. And this kind of slip of the fault can be expressed by sliding weakening friction criterion or a friction criterion related to rate and state. The super shear rupture may occur in the horizontal direction of the plane S wave and Maher wave in the horizontal direction. These waves will significantly enhance the ground motion and destructive force in the direction of fault rupture. That is, it has stronger energy radiation. The slip behavior of the seismic fault and the fracture process of the fault layer are closely related to the surrounding geological environment. Correlation, such as the stress disturbance or pore pressure change of the fault may affect the period of the earthquake and the magnitude of the earthquake (long time scale, year). It may also impede the rupture of the fault or trigger the super shear rupture (short time scale, second). The physical process and the earthquake prevention and disaster reduction work have important theoretical and practical significance. This paper intends to study the influence of the ambient stress changes on the slip behavior of the fault and the rupture process of the fault surface by establishing the physical model. In particular, the finite element method and the sliding weakening friction criterion are used to simulate the fracture. The process of layer stress loading to recognize the sliding law of the fault and explore the dynamic fracture process of the fault in order to deepen the understanding of the physical process of the earthquake, and provide some valuable scientific basis for the earthquake prevention and reduction. The sliding law and the effect of the stress disturbance are studied. Then, taking the 2011 Tohoku Mw9.0 earthquake in Japan as a concrete example, a two-dimensional curve fault numerical model is set up, and the high precision deformation observation is used to restrain the model. Finally, in the two-dimensional plane strike slip layer, the obstacle (B) with the increase of local effective positive stress is studied. The main results are as follows: (1) the main results are as follows: (1) the numerical results show that, under the uniform stress distribution, the plane fault slide shows typical characteristic seismic law, the stress disturbance on the fault surface affects the fault slip law, and the pressure stress increases obviously and increases the time of the earthquake. The influence of the stress disturbance on the critical area of the earthquake rupture is more significant than that of the slip zone before the earthquake. When the stress disturbance occurs in the earthquake zone, if the stress disturbance is large enough, the increase of the pressure stress will result in the temporary locking of some dynamic faults when the earthquake occurs, so that the energy released by the earthquake will be smaller, but the follow-up can increase the follow-up. The energy of an earthquake, and the decrease of the pressure stress can cause more complex changes in the law of the earthquake, which triggers the earthquake immediately. If the stress disturbance occurs at the early stage of an earthquake cycle, the triggered earthquake is smaller, but it can lead to a subsequent earthquake to occur in advance; if the stress disturbance occurs in the later period of an earthquake period, it will trigger. A large earthquake. When the stress disturbance is located in the slip zone or the critical zone before the earthquake, small disturbances may also have similar effects. The later the stress disturbance occurs, the more obvious the effect is. The effect of the stress disturbance on the critical zone is most obvious. The effect of the stress disturbance is mainly concentrated on the 1-2 earthquake weeks after the stress is disturbed. During the period of the earthquake, the following earthquake basically recovered the characteristic seismic law without stress disturbance. (2) the numerical simulation results show that the model shows the characteristics of repeated earthquakes with 6 large earthquakes in 1000 years. The numerical results of the model are consistent with the GPS displacement of the ground surface and the GPS velocity distribution between the earthquakes. In addition, the model results are also obvious. A small earthquake occurs in the middle of the two large earthquakes. The repetition period of the large earthquake is about 161 years, the size of the unit rupture length is about 1.13 x 1020N m/km, and the seismic moment of the small earthquake is about 5.62 x 1018Nm/km.. The calculation results show that the viscosity of the rock rock ring and the soft flow circle of the model mantle wedge has the GPS velocity between the earthquakes. There is a significant impact on the field. The viscosity of the lithosphere and the asthenosphere of the mantle wedge exists in the parameter medium. If the viscosity of the asthenosphere decreases from 1020 Pa s to 2.5 x 1019 Pa s, the viscosity of the model mantle wedge lithosphere needs to be increased from 1020 Pa s to 2.5 * 1020 Pa S. numerical calculation. During the earthquake period, the spatial gravity change values and the ground point gravity change values vary with time, which can reach -366 gal and 667 gal respectively in the continental margin of the trench, but on the land, the change is smaller and the maximum change is about 200 km from the trench, and the change value is about 159 Mu gal and -77 Mu gal, and the change of the velocity field is mainly occurring. After about 5 years after the earthquake, it has been basically stable after the earthquake. (3) the simulation results show that the obstacle not only slows down or prevents the propagation of earthquake rupture, but also may trigger the super shear rupture. The results show that the super shear rupture occurs within a parameter region, and this region is between two linear boundaries. The width of the obstacle body is below the lower boundary, then the earthquake rupture can overcome this obstacle and keep the velocity of the subshear rupture. If the width of the obstacle is above the upper boundary, the obstacle can always prevent the propagation of the earthquake rupture. In addition, this paper also shows that this kind of overshoot is triggered by the obstacle body. The propagation of shear rupture may eventually decelerate to subshear, which depends on the width and position of the barrier body. As the width of the barrier increases from the lower boundary to the upper boundary, the reduction of the main rupture velocity caused by the obstacle increases gradually, and the continuous distance of the propagation of the super shear rupture increases. These results indicate that the fault is on the fault. The barrier body may not prevent the propagation of earthquake rupture, but may trigger the transition of super shear rupture. This super shear fracture transition has a very important influence on the near field strong ground motion and the earthquake damage force.

【學(xué)位授予單位】：中國(guó)科學(xué)技術(shù)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：P315

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