| By far, the elastic rebound theory is considered as the main mechanism of tectonic earthquake. The so-called elastic rebound theory is that crustal rock around the fault deforms under tectonic stress loading and gradually accumulates stress and strain energy. When the shear stress reaches certain threshold, the fault bounds abruptly, i.e, earthquakes occur, accompanied by the release of stress and strain energy. Geological survey and rock physics experiments show that this earthquakes process could be simplified as the stick-slip behavior of fault. In addition, the stick-slip behavior of fault could be represented by the friction constitutive relations that is the slip-weakening friction law or the rate and state friction law. Research also show that the rupture may propagate faster than the shear wave velocities, i.e., supershear rupture. The supershear rupture could produce horizontally expanding planar S and surface wave Mach waves that enhance ground shaking and damage near the direction of rupture propagation, affecting wave energy distribution. The stick-slip behavior of fault and coseismic rupture process are highly related to ambient environment, such as the stress change of the fault or pore pressure variation could affect the pattern of the earthquake cycle and seismic moment (long-time scale, year), and the coseismic rupture process (short-time scale, second), i.e., stopping the rupture or inducing supershear. To improve the knowledge of the pattern of the earthquake cycle, we need to understand the influence of stress change on earthquake cycle physically and coseismic rupture process.We want to study the the influence of ambient stress change on earthquake cycle physically and coseismic rupture process. Specifically, we use the finite element method and the slip-weakening friction law by simulating the stress loading of the fault to understand stick-slip behavior and coseismic rupture process. Hope to improve our knowledge about the earthquake process. First, we consider the influences of stress disturbance on earthquake cycles based on a 2D finite element model by employing a dynamic fault with slip-weakening friction law; then consider a 2D finite element model that simulates earthquake cycle process controlled by the physical laws based on the slip weakening friction law comparing with the case of Japan Tohoku Mw9.0 earthquake; and consider the effects of a patch with elevated effective normal stress (barrier) on two-dimensional in-plane rupture propagation on a planar fault from numerical experiments. The main results as follows:(1) Numerical results show that the stick-slip process of the dynamic fault in a model with uniform background stress behaves like typical characteristic earthquakes, which could be influenced by stress disturbance on the fault. Increasing pressure or decreasing normal stress on the fault delays the occurrence of the following earthquake and enlarges its size, which is more prominent if the stress disturbance locates on the critical rupture zone than on pre-seismic slip zone. If the increased pressure locates on the earthquake slip zone and is large enough, part of the dynamic fault could be locked temporally, thus decreasing the following earthquake size, but enlarging the next earthquake. The influence of decreasing pressure on the fault is more complicate than increasing pressure. If the decreased pressure is large enough, an earthquake could be triggered immediately. If the pressure is decreased at earlier stage of an earthquake cycle, the triggered earthquake usually is a small one, and the next earthquake happens at a shorter time than the time interval of the characteristic earthquakes; on contrary, if the pressure is decreased at later stage of an earthquake cycle, a large earthquake will be triggered immediately. If the stress disturbance locates on pre-seismic slip zone or critical rupture zone, a smaller stress disturbance could produce a similar result; and the later disturbance happens the more prominent the influence is. The influences are the most prominent when disturbance locates on critical rupture zone. It should be pointed out that the influences of stress disturbance are usually confined within one or two earthquake cycles and the following earthquake cycles are nearly identical with those without stress disturbance.(2) The simulation result shows that the typical law of the characteristic earthquake during 1000 years. The coseismic and interseismic surface deformation of the model agrees well with the GPS observations. The repeated intervals of the earthquake cycle are about 161±4 years and the seismic moments of rupture unit length are about 1.13×102 N m/km, and the result also shows there is a small earthquake whose seismic moment is about 5.62×1018N m/km occurring between the large earthquakes. The result further shows that the values of viscosity of continental mantle lithosphere and asthenosphere have significance influence on the interseismic GPS velocity field, and if the value of viscosity of continental asthenosphere reduces from 1020Pa s to 2.5×1019Pa s, then the value of viscosity of continental lithosphere must increase from 1020Pa s to 2.5×1020 Pa s for the consistency between the interseismic GPS velocity field and the model result. The result also shows that the change of the free-air and the ground point of gravity anomaly of this model can reach about-378μgal and 655μgal near trench respectively during an earthquake cycle, varying linearly during the interseismic period, and the changes of those are lesser on land where the maximum value is about 186μ gal and-51μ gal near 200 km from the trench. The horizontal velocity field mainly keeps increasing stably about 5 years after the earthquake.(3) Our results confirm that the barrier may slow down or stop coseismic ruptures, but may also induce supershear ruptures. We demonstrate that the supershear rupture may emerge in a region that is delineated by two approximate linear boundaries. If the barrier size is below the lower boundary, ruptures can overcome the barrier and propagate at subshear speeds. If the barrier size is larger than the upper boundary, ruptures are always stopped by the barrier. Furthermore, we find that the barrier-induced supershear ruptures may eventually slow down into subshear speed, depending on the size and the location of the barrier. The duration of supershear ruptures increases as the barrier sizes grow from the lower to the upper boundary, which are proportional to the reduction in rupture speeds caused by the barrier. These results indicate that a barrier on the fault may not stop coseismic ruptures. Rather, the barrier may induce ruptures propagating at supershear speeds that play important roles in near-field ground shaking and damage. |
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