Browsing by Author "Sattari, Arsalan"

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    Finite Element Modelling of Induced Rupture on Faults with Non-negligible Cohesion
    (2018-09-05) Sattari, Arsalan; Eaton, David W.; Garagash, Dmitry I.; Krebes, Edward Stephen; Davidsen, Jörn; Lauer, Rachel M.
    A finite-element (FE) simulation approach is used to investigate earthquake rupture processes on faults with cohesion. This study is motivated by evidence that, unlike tectonically active systems, faults that have been inactive on a timescale of centuries or longer (well-healed faults) have non-negligible cohesion. Inclusion of cohesion, along with friction, into the basic physical model for fault activation may be important for calculating hazards associated with injection-induced seismicity, where earthquakes are typically concentrated in formerly quiescent regions. The problems addressed in this thesis are framed by a series of hypotheses: 1) cohesion loss plays a key role in stress drop and seismic efficiency of well-healed faults; 2) co-seismic stress drop affects only the shear stress acting on a fault in proximity to a free surface; 3) inclusion of dynamic processes in the numerical simulation, such as slip overshoot, has an important effect on the magnitude of surface deformation; 4) fault slip is modified by coupling between dynamic rupture and body waves in the surrounding medium. Chapter 2 tests hypotheses 1 and 2 using an adapted and improved version of a 2-D plane-strain, static FE modelling method for a dip-slip fault. The result of the model is in good agreement with analytical models and shows that both cohesion and friction loss can contribute to stress drop. Chapter 3 uses a similar FE model setup to address hypotheses 1, 2 and 3. In this case, a dynamic FE method is used in which d'Alembert forces (inertial components) are considered, leading to slip overshoot. The results indicate that seismic efficiency increases with the ratio of cohesion to normal stress. A previous theoretical model that places an upper bound on seismic efficiency (0.06) is therefore valid only if cohesion is neglected. Chapter 4 tests hypothesis 4 using a suite of 3-D dynamic FE models of strike-slip faulting, a more common mechanism for induced earthquakes. Rupture is initiated by abrupt loss of cohesion within a discrete fault patch (asperity), thereupon propagating outwards into a marginally stable region of the fault. The results indicate that cohesion loss is sufficient to sustain dynamic rupture. Modelled oscillatory behavior of stress drop is interpreted to be a footprint of dynamic interaction between the rupture front and body waves propagating in the surrounding rockmass.