Conditions for the occurrence of seismic sequences in a fault system

Dragoni, Michele; Lorenzano, Emanuele

doi:10.5194/npg-23-419-2016

Cited by 6 publications

(6 citation statements)

References 24 publications

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“…In fact, from (5) and (6), we have For nonoverlapping regions, it is a good approximation to use tractions produced by pointlike dislocations (e.g. Dragoni and Lorenzano 2016) …”

Section: Discussionmentioning

confidence: 99%

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Dynamics of a fault model with two mechanically different regions

Dragoni

Lorenzano

2017

Earth Planets Space

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We consider a fault containing two regions with different mechanical behaviours: a strong, velocity-weakening region (asperity) and a weak, velocity-strengthening region. The fault is embedded in a shear zone subject to a constant strain rate by the motions of adjacent tectonic plates. The fault is modelled as a discrete dynamical system whose state is described by two variables expressing the slip deficits of the two regions. Because of plate motion, the asperity accumulates stress and eventually releases it, producing an earthquake, when a frictional threshold is exceeded. The weak region is subject to a very slow creep during interseismic intervals and may slip at a higher rate (afterslip) as a consequence of coseismic stress imposed by the asperity failure. The evolution equations of the system are solved analytically for the interseismic intervals, the asperity slip and the afterslip in the weak region. It is found that the amount of afterslip is proportional to the seismic slip of the asperity, in agreement with observations. The model shows that afterslip is a natural consequence of seismic slip in a fault containing a velocity-strengthening region. Afterslip may have any duration, according to the intensity of velocity strengthening, thus accounting for the wide range of observed durations. The model is applied to the fault of the 2011 Tohoku-Oki earthquake. The results suggest that the first four months after the event were dominated by afterslip, while the subsequent postseismic deformation was probably due to viscoelastic relaxation in the asthenosphere.

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“…In fact, from (5) and (6), we have For nonoverlapping regions, it is a good approximation to use tractions produced by pointlike dislocations (e.g. Dragoni and Lorenzano 2016) …”

Section: Discussionmentioning

confidence: 99%

“…We assume an average dip angle δ = 20 • (Lay et al 2012). The strain rate on the fault is then (Dragoni and Lorenzano 2016) Fig. 6 Geometrical illustration of the cycle made of seismic slip, afterslip and interseismic creep.…”

Section: An Application: the 2011 Tohoku-oki Earthquakementioning

confidence: 99%

Dynamics of a fault model with two mechanically different regions

Dragoni

Lorenzano

2017

Earth Planets Space

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“…Another source of complication may be represented by the interaction between viscoelastic relaxation and stable creep on the fault. This problem is beyond the scope of the present work, but it may be object of future research by combining elements of the present model with the one of Dragoni and Lorenzano (2017).…”

Section: Discussionmentioning

confidence: 98%

“…In the present model we do not consider aseismic slip on the fault. It has been treated in the framework of a discrete fault model by Dragoni and Lorenzano (2017), who considered a region slipping aseismically for a finite time interval and calculated the effect on the stress distribution and the subsequent evolution of the fault. Of course, if the amplitude of aseismic slip has the same order of magnitude as that of seismic slip, the fault evolution may be affected.…”

Section: The Modelmentioning

confidence: 99%

Complex interplay between stress perturbations and viscoelastic relaxation in a two-asperity fault model

Lorenzano

Dragoni

2018

Nonlin. Processes Geophys.

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Abstract. We consider a plane fault with two asperities embedded in a shear zone, subject to a uniform strain rate owing to tectonic loading. After an earthquake, the static stress field is relaxed by viscoelastic deformation in the asthenosphere. We treat the fault as a discrete dynamical system with 3 degrees of freedom: the slip deficits of the asperities and the variation of their difference due to viscoelastic deformation. The evolution of the fault is described in terms of inter-seismic intervals and slip episodes, which may involve the slip of a single asperity or both. We consider the effect of stress transfers connected to earthquakes produced by neighbouring faults. The perturbation alters the slip deficits of both asperities and the stress redistribution on the fault associated with viscoelastic relaxation. The interplay between the stress perturbation and the viscoelastic relaxation significantly complicates the evolution of the fault and its seismic activity. We show that the presence of viscoelastic relaxation prevents any simple correlation between the change of Coulomb stresses on the asperities and the anticipation or delay of their failures. As an application, we study the effects of the 1999 Hector Mine, California, earthquake on the post-seismic evolution of the fault that generated the 1992 Landers, California, earthquake, which we model as a two-mode event associated with the consecutive failure of two asperities.

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“…This is 5 good approximation for nonoverlapping regions (Dragoni and Lorenzano, 2016). Let m 0 be the scalar seismic moment of the dislocation.…”

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Complex interplay between stress perturbations and viscoelastic relaxation in a two-asperity fault model

Lorenzano¹,

Dragoni²

2017

Preprint

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Abstract. We consider a plane fault with two asperities embedded in a shear zone, subject to a uniform strain rate owing to tectonic loading. After an earthquake, the static stress field is relaxed by viscoelastic deformation. We treat the fault as a discrete dynamical system with three degrees of freedom: the slip deficits of the asperities and the variation of their difference due to viscoelastic deformation. The dynamics of the system is described in terms of one sticking mode and three slipping modes. We consider the effect of stress transfers connected to earthquakes produced by neighbouring faults. The perturbation 5 is studied in terms of a vector in the state space, whose components are the changes in the state variables of the system. The interplay between the stress perturbation and the viscoelastic relaxation significantly complicates the evolution of the fault and its seismic activity. We show that the presence of viscoelastic relaxation prevents any simple correlation between the change of Coulomb stresses on the asperities and the anticipation or delay of their failures. As an application, we study the effects of the 1999 Hector Mine, California, earthquake on the post-seismic evolution of the fault that generated the 1992 Landers, 10California, earthquake, which we model as a two-mode event associated with the consecutive failure of two asperities.Copyright statement. All authors have approved the manuscript for submission. The content of the manuscript has not been published or submitted elsewhere.

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Conditions for the occurrence of seismic sequences in a fault system

Cited by 6 publications

References 24 publications

Dynamics of a fault model with two mechanically different regions

Dynamics of a fault model with two mechanically different regions

Complex interplay between stress perturbations and viscoelastic relaxation in a two-asperity fault model

Complex interplay between stress perturbations and viscoelastic relaxation in a two-asperity fault model

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