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Abstract We develop an earthquake simulator to study the partitioning of seismic/aseismic slip and dynamics of Earthquakes on a Heterogeneous strike‐slip Fault (HFQsim) using a generalized model of a discrete fault governed by static/dynamic friction and creep in an elastic half‐space. Previous versions of the simulator were shown to produce various realistic seismicity patterns (e.g., frequency‐magnitude event statistics, hypocenter and slip distributions, temporal occurrence) using friction levels and creep properties that vary in space but are fixed in time. The new simulator incorporates frictional heat generation by earthquake slip leading to temperature rises, subsequent diffusion cooling into the half space, and time‐dependent creep on the fault. The model assumes a power law dependence of creep velocity on the local shear stress, with temperature‐dependent coefficients based on the Arrhenius equation. Temperature rises due to seismic slip produce increased aseismic slip, which can lead to further stress concentrations, aftershocks, and heat generation in a feedback loop. The partitioning of seismic/aseismic slip and space‐time evolution of seismicity are strongly affected by the temperature changes on the fault. The results are also affected significantly by the difference between the static and kinetic friction levels. The model produces realistic spatio‐temporal distribution of seismicity, transient aseismic slip patterns, mainshock‐aftershock sequences, and a bimodal distribution of earthquakes with background and clustered events similar to observations. The HFQsim may be used to clarify relations between fault properties and different features of seismicity and aseismic slip, and to improve the understanding of failure patterns preceding large earthquakes.
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Cascading foreshocks, aftershocks and earthquake swarms in a discrete fault network
SUMMARY Earthquakes come in clusters formed of mostly aftershock sequences, swarms and occasional foreshock sequences. This clustering is thought to result either from stress transfer among faults, a process referred to as cascading, or from transient loading by aseismic slip (pre-slip, afterslip or slow slip events). The ETAS statistical model is often used to quantify the fraction of clustering due to stress transfer and to assess the eventual need for aseismic slip to explain foreshocks or swarms. Another popular model of clustering relies on the earthquake nucleation model derived from experimental rate-and-state friction. According to this model, earthquakes cluster because they are time-advanced by the stress change imparted by the mainshock. This model ignores stress interactions among aftershocks and cannot explain foreshocks or swarms in the absence of transient loading. Here, we analyse foreshock, swarm and aftershock sequences resulting from cascades in a Discrete Fault Network model governed by rate-and-state friction. We show that the model produces realistic swarms, foreshocks and aftershocks. The Omori law, characterizing the temporal decay of aftershocks, emerges in all simulations independently of the assumed initial condition. In our simulations, the Omori law results from the earthquake nucleation process due to rate and state friction and from the heterogeneous stress changes due to the coseismic stress transfers. By contrast, the inverse Omori law, which characterizes the accelerating rate of foreshocks, emerges only in the simulations with a dense enough fault system. A high-density complex fault zone favours fault interactions and the emergence of an accelerating sequence of foreshocks. Seismicity catalogues generated with our discrete fault network model can generally be fitted with the ETAS model but with some material differences. In the discrete fault network simulations, fault interactions are weaker in aftershock sequences because they occur in a broader zone of lower fault density and because of the depletion of critically stressed faults. The productivity of the cascading process is, therefore, significantly higher in foreshocks than in aftershocks if fault zone complexity is high. This effect is not captured by the ETAS model of fault interactions. It follows that a foreshock acceleration stronger than expected from ETAS statistics does not necessarily require aseismic slip preceding the mainshock (pre-slip). It can be a manifestation of a cascading process enhanced by the topological properties of the fault network. Similarly, earthquake swarms might not always imply transient loading by aseismic slip, as they can emerge from stress interactions.
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- Award ID(s):
- 1822214
- PAR ID:
- 10434881
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Geophysical Journal International
- Volume:
- 235
- Issue:
- 1
- ISSN:
- 0956-540X
- Format(s):
- Medium: X Size: p. 831-852
- Size(s):
- p. 831-852
- Sponsoring Org:
- National Science Foundation
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