Elastodynamic analysis of earthquake sequences on slowly loaded faults with rate and state friction (original) (raw)
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Nucleation and early seismic propagation of small and large events in a crustal earthquake model
Journal of Geophysical Research: Solid Earth, 2003
Earthquake nucleation and early seismic propagation are studied in a two-dimensional strike-slip fault model with depth-variable properties. The fault is governed by the Dieterich-Ruina rate and state friction law. We use an efficient and rigorous numerical procedure for elastodynamic analysis of earthquake sequences on slowly loaded faults developed by Lapusta et al. [2000]. We find that for decreasing values of the characteristic slip distance of the friction law, small events appear at the transition from the locked to creeping behavior toward the bottom of the seismogenic zone. Small and large events have very similar nucleation phases in our simulations. Here, by ''nucleation phase'' we mean gradually accelerating aseismic slip in a small slowly expanding zone before the breakout of the dynamic, seismically detectable event. Moment acceleration (to which velocity seismograms are proportional) in early stages of seismic propagation exhibits irregular fluctuations, in the form of speedups and slowdowns in the moment release rate, consistently with observations as reported by Ellsworth and Beroza [1995]. Our simulations show that such irregular moment acceleration can, at least in part, be due to the heterogeneous stress distribution imprinted on the fault by the arrest of previous small events and by stress concentrations at the borders of creeping regions and to partial arrest of the rupture in velocity-strengthening fault regions which inhibit seismic slip.
Influence of friction and fault geometry on earthquake rupture
Journal of Geophysical Research, 2000
We investigate the impact of variations in the friction and geometry on models of fault dynamics. We focus primarily on a three-dimensional continuum model with scalar displacements. Slip occurs on an embedded two-dimensional planar interface. Friction is characterized by a two-parameter rate and state law, incorporating a characteristic length for weakening, a characteristic time for healing, and a velocity-weakening steady state. As the friction parameters are varied, there is a crossover from narrow, self-healing slip pulses to crack-like solutions that heal in response to edge effects. For repeated ruptures the crack-like regime exhibits periodic or aperiodic systemwide events. The self-healing regime exhibits dynamical complexity and a broad distribution of rupture areas. The behavior can also change from periodicity or quasi-periodicity to dynamical complexity as the total fault size or the length-to-width ratio is increased. Our results for the continuum model agree qualitatively with analogous results obtained for a one-dimensional Burridõe-Knopoff model in which radiation effects are approximated by viscous dissipation. context of a three-dimensional continuum model and a one-dimensional Burridge-Knopoff model. In our studies, dynamical complexity refers to observations of a
Earthquake activity related to seismic cycles in a model for a heterogeneous strike-slip fault
Tectonophysics, 2006
We investigate the evolution of seismicity within large earthquake cycles in a model of a discrete strike-slip fault in elastic solid. The model dynamics is governed by realistic boundary conditions consisting of constant velocity motion of regions around the fault, static/kinetic friction and dislocation creep along the fault, and 3D elastic stress transfer. The fault consists of brittle parts which fail during earthquakes and undergo small creep deformation between events, and aseismic creep cells which are characterized by high ongoing creep motion. This mixture of brittle and creep cells is found to generate realistic aftershock sequences which follow the modified Omori law and scale with the mainshock size. Furthermore, we find that the distribution of interevent times of the simulated earthquakes is in good agreement with observations. The temporal occurrence, however, is magnitude-dependent; in particular, the small events are clustered in time, whereas the largest earthquakes occur quasiperiodically. Averaging the seismicity before several large earthquakes, we observe an increase of activity and a broadening scaling range of magnitudes when the time of the next mainshock is approached. These results are characteristics of a critical point behavior. The presence of critical point dynamics is further supported by the evolution of the stress field in the model, which is compatible with the observation of accelerating moment release in natural fault systems.
Shear and normal load perturbations on a two-dimensional continuous fault: 2. Dynamic triggering
[1] We study the consequences of temporal stress perturbations on earthquake nucleation in a continuous fault model. Using a two-dimensional (2-D) quasi-dynamic model of a strike-slip fault governed by a rate-and-state friction law with depth variable properties, we show that dynamic triggering (due to stress pulses or wave packets), although allowed by our results, is an exception rather than a rule and should be limited to understressed areas such as areas of high pore pressures or to faults at the very end of their earthquake cycle. When periodic stress perturbations are sensitive, the response of the fault is frequency-independent for periods lower than a period T 0 but strongly depends on the frequency for periods larger than T 0. We demonstrate that the crossover period T 0 is equal to the time left until the earthquake instability. According to our model, high frequencies are demonstrated to have a higher triggering potential than low ones, which makes tidal triggering very unlikely before the end of the cycle due to the very low amplitudes of the stress perturbations involved. INDEX TERMS: 7209 Seismology: Earthquake dynamics and mechanics; 7215 Seismology: Earthquake parameters; 7260 Seismology: Theory and modeling; KEYWORDS: earthquake triggering, dynamic triggering, Coulomb stress change, rate and state friction laws, clock advance/delay Citation: Perfettini, H., J. Schmittbuhl, and A. Cochard, Shear and normal load perturbations on a two-dimensional continuous fault: 2.
Dynamics of a creep-slip model of earthquake faults
Physica A: Statistical Mechanics and its Applications, 1998
Starting o from the relationship between time-dependent friction and velocity softening we present a generalization of the continuous, one-dimensional homogeneous Burridge-Knopo (BK) model by allowing for displacements by plastic creep and rigid sliding. The evolution equations describe the coupled dynamics of an order parameter-like ÿeld variable (the sliding rate) and a control parameter ÿeld (the driving force). In addition to the velocity-softening instability and deterministic chaos known from the BK model, the model exhibits a velocitystrengthening regime at low displacement rates which is characterized by anomalous di usion and which may be interpreted as a continuum analogue of self-organized criticality (SOC). The governing evolution equations for both regimes (a generalized time-dependent Ginzburg-Landau equation and a non-linear di usion equation, respectively) are derived and implications with regard to fault dynamics and power-law scaling of event-size distributions are discussed. Since the model accounts for memory friction and since it combines features of deterministic chaos and SOC it displays interesting implications as to (i) material aspects of fault friction, (ii) the origin of scaling, (iii) questions related to precursor events, aftershocks and afterslip, and (iv) the problem of earthquake predictability. Moreover, by appropriate re-interpretation of the dynamical variables the model applies to other SOC systems, e.g. sandpiles.
We estimate the critical slip-weakening distance on earthquake faults by using a new approach, which is independent of the estimate of fracture energy or radiated seismic energy. The approach is to find a physically based relation between the breakdown time of shear stress T b , the time of peak slip-velocity T pv , and the slip-weakening distance D c , from the time histories of shear stress, slip, and slip velocity at each point on the fault, which can be obtained from dynamic rupture calculations using a simple slip-weakening friction law. Numerical calculations are carried out for a dynamic shear crack propagating either spontaneously or at a fixed rupture velocity on a vertical fault located in a 3D half-space and a more realistic horizontally layered structure, with finite-difference schemes. The results show that T pv is well correlated with T b for faults even with a heterogeneous stress-drop distribution, except at locations near strong barriers and the fault edges. We also investigate this relation for different types of slip-weakening behavior.
Geochemistry Geophysics Geosystems, 2021
Seismically active faults pose a major threat to many communities worldwide. Therefore, it is vital to make appropriate predictions on the probability of large earthquakes and their associated effects, such as tsunamis and mass movements. Several factors contribute to the difficulties to estimate seismic hazard in the vicinity of such faults. Besides the vulnerability of structures and the societal impact, geological factors play an important role in seismic hazard assessment and the development of models that describe fault activity (Zöller & Hainzl, 2007). Current models for earthquake recurrence incorporate mathematical models of earthquake statistics (Gutenberg-Richter, Omori-Utsu-Aftershocks, Brownian-First-Passage-Time), numerical models of earthquakes and rupture processes (Rate-and-State-Friction), interseismic stress built-up and the interaction of multiple faults over a larger area via stress transfer (e.g.,