978 research outputs found
Near mean-field behavior in the generalized Burridge-Knopoff earthquake model with variable range stress transfer
Simple models of earthquake faults are important for understanding the
mechanisms for their observed behavior in nature, such as Gutenberg-Richter
scaling. Because of the importance of long-range interactions in an elastic
medium, we generalize the Burridge-Knopoff slider-block model to include
variable range stress transfer. We find that the Burridge-Knopoff model with
long-range stress transfer exhibits qualitatively different behavior than the
corresponding long-range cellular automata models and the usual
Burridge-Knopoff model with nearest-neighbor stress transfer, depending on how
quickly the friction force weakens with increasing velocity. Extensive
simulations of quasiperiodic characteristic events, mode-switching phenomena,
ergodicity, and waiting-time distributions are also discussed. Our results are
consistent with the existence of a mean-field critical point and have important
implications for our understanding of earthquakes and other driven dissipative
systems.Comment: 24 pages 12 figures, revised version for Phys. Rev.
Gutenberg-Richter statistics in topologically realistic system-level earthquake stress-evolution simulations
We discuss the problem of earthquake forecasting in the context of new models for the dynamics based on statistical physics. Here we focus on new, topologically realistic system-level approaches to the modeling of earthquake faults. We show that the frictional failure physics of earthquakes in these complex, topologically realistic models leads to self-organization of the statistical dynamics, and produces statistical distributions characterizing the activity, notably the Gutenberg-Richter magnitude frequency distribution, that are similar to those observed in nature. In particular, we show that a parameterization of friction that includes a simple representation of a dynamic stress intensity factor is needed to organize the dynamics. We also show that the slip distributions for synthetic events obtained in the model are also similar to those observed in nature
Application of an inhomogeneous stress (patch) model to complex subduction zone earthquakes: A discrete interaction matrix approach
In recent years it has been recognized that the level of shear and normal stress along a fault can vary; thus the stress is spatially and temporally inhomogeneous. Moreover, it has also been suspected that faults might interact in some way, with the result that a variety of earthquake magnitudes might be produced along a given length of fault at varying times. In order to explore these ideas we have developed a quantitative formalism, which we call the interaction matrix method, to express the influence of one fault upon another. This matrix is calculated by use of the energy change for a system of interacting cracks or faults and therefore gives energy-consistent results. Specifically, the interaction matrix relates the area-averaged stress on the fault segment to the area-averaged slip state on all the other fault segments in the system. Since any fault can be subdivided into an arbitrary number of fault segments, the interaction matrix can have arbitrary dimension; in fact, the continuum limit is recovered as the dimension of the matrix approaches infinity. We combine this matrix method with a segmentation, or “patch,” model for earthquakes, in which each discrete segment of a fault has the same coseismic stress change (defined as the difference between the driving stress at which healing occurs minus the driving stress at which sliding starts) each time it slips. We show that slip on a patch during an earthquake can vary substantially, depending on how it interacts with other nearby patches. In this model it is quite possible for the spatial distribution of stress on the fault following an event to be again in a spatially inhomogeneous state, rather than in a uniform state, as is often assumed. Hence the seismic moment produced by an earthquake on a given set of patches can vary substantially, depending on the sequence of sliding and healing on the different patches. To apply these ideas, we devised a means to calculate the interaction matrix elements and used them to quantitatively examine earthquake sequences off the Colombia-Ecuador coast and in the Nankai Trough near Japan
Natural Time, Nowcasting and the Physics of Earthquakes: Estimation of Seismic Risk to Global Megacities
This paper describes the use of the idea of natural time to propose a new
method for characterizing the seismic risk to the world's major cities at risk
of earthquakes. Rather than focus on forecasting, which is the computation of
probabilities of future events, we define the term seismic nowcasting, which is
the computation of the current state of seismic hazard in a defined geographic
region.Comment: 9 Figures, 4 Table
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