A Physical Model for Interseismic Erosion of Locked Fault Asperities

Mavrommatis, A. P.; Segall, P.; Johnson, K. M.

doi:10.1002/2017jb014533

Cited by 18 publications

(16 citation statements)

References 59 publications

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“…Repeating events (Kato et al, 2016; Kato & Nakagawa, 2014; Meng et al, 2015; Figure 2) and observed GPS surface displacement transients (Bedford et al, 2015; Herman et al, 2015; Ruiz et al, 2014) during the foreshock sequence suggest that aseismic slip was accompanying or even driving the preseismic activity. Dynamic seismic cycle simulations using rate‐and‐state friction laws showed that frictionally locked asperities get eroded at the margins by creep penetrating at the late stage of the seismic cycle (Hori & Miyazaki, 2010; Lapusta & Liu, 2009; Mavrommatis et al, 2017). Our observed interseismic and preseismic activity is likely an expression of this dynamic erosion process around asperities.…”

Section: Discussionmentioning

confidence: 99%

Forming a Mogi Doughnut in the Years Prior to and Immediately Before the 2014 M8.1 Iquique, Northern Chile, Earthquake

Schurr

Moreno

Tréhu

et al. 2020

Geophysical Research Letters

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Asperities are patches where the fault surfaces stick until they break in earthquakes. Locating asperities and understanding their causes in subduction zones is challenging because they are generally located offshore. We use seismicity, interseismic and coseismic slip, and the residual gravity field to map the asperity responsible for the 2014 M8.1 Iquique, Chile, earthquake. For several years prior to the mainshock, seismicity occurred exclusively downdip of the asperity. Two weeks before the mainshock, a series of foreshocks first broke the upper plate then the updip rim of the asperity. This seismicity formed a ring around the slip patch (asperity) that later ruptured in the mainshock. The asperity correlated both with high interseismic locking and a circular gravity low, suggesting that it is controlled by geologic structure. Most features of the spatiotemporal seismicity pattern can be explained by a mechanical model in which a single asperity is stressed by relative plate motion.

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Section: Discussionmentioning

confidence: 99%

Forming a Mogi Doughnut in the Years Prior to and Immediately Before the 2014 M8.1 Iquique, Northern Chile, Earthquake

Schurr

Moreno

Tréhu

et al. 2020

Geophysical Research Letters

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“…where K l is the SIF due to displacement at a ≥ R, which we assume to grow linearly in time (S = v pl t). The propagating creep front can be treated as an annular crack driven by edge displacement, which grows in response to an increase in the displacement boundary condition (analogous to the 2-D case analyzed by Mavrommatis et al, 2017). We consider an annular crack with outer radius R and inner radius a(t).…”

Section: Appendix A: Creep Front Propagationmentioning

confidence: 99%

Crack Models of Repeating Earthquakes Predict Observed Moment‐Recurrence Scaling

Cattania

Segall

2019

JGR Solid Earth

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Small repeating earthquakes are thought to represent rupture of isolated asperities loaded by surrounding creep. The observed scaling between recurrence interval and seismic moment, T r ∼ M 1∕6 , contrasts with expectation assuming constant stress drop and no aseismic slip (T r ∼ M 1∕3 ). Here we demonstrate that simple crack models of velocity-weakening asperities in a velocity-strengthening fault predict the M 1∕6 scaling; however, the mechanism depends on asperity radius, R. For small asperities (R ∞ < R < 2R ∞ , where R ∞ is the nucleation radius) numerical simulations with rate-state friction show interseismic creep penetrating inward from the edge, and earthquakes nucleate in the center and rupture the entire asperity. Creep penetration accounts for ∼25% of the slip budget, the nucleation phase takes up a larger fraction of slip. Stress drop increases with increasing R; the lack of self-similarity being due to the finite nucleation dimension. For 2R ∞ < R ≲ 6R ∞ simulations exhibit simple cycles with ruptures nucleating from the edge. Asperities with R ≳ 6R ∞ exhibit complex cycles of partial and full ruptures. Here T r is explained by an energy criterion: full rupture requires that the energy release rate everywhere on the asperity at least equals the fracture energy, leading to the scaling T r ∼ M 1∕6 . Remarkably, in spite of the variability in behavior with source dimension, the scaling of T r with stress drop Δ , nucleation length and creep rate v pl is the same across all regimes:This supports the use of repeating earthquakes as creepmeters and provides a physical interpretation for the scaling observed in nature. Plain Language SummaryWhile most earthquake sequences have complex temporal patterns, some small earthquakes are quite predictable: they repeat periodically. The time between consecutive events (recurrence interval) grows with earthquake size: as intuitive, it takes longer to accumulate the mechanical energy for large earthquakes. However, the scaling between the recurrence interval and earthquake energy (seismic moment) is not what simple physical considerations predict. It is often assumed that faults are locked between events and seismic slip must therefore keep up with long-term plate motion. This leads to the scaling: T r ∼ M 1∕3 0 , but the observed scaling is T r ∼ M 1∕6 0 . In fact, faults are not fully locked between earthquakes: they can slip slowly, or release part of the energy in smaller quakes between the larger ones. Here we use numerical simulations, and ideas from fracture mechanics, to understand what controls the time between repeating quakes. The main results are (1) analytical expressions of the recurrence interval as a function of earthquake size, predicting the observed scaling; (2) explanation of the differences between the cycle of small and large earthquakes (fraction of slow slip, direction of rupture propagation, and the occurrence of smaller quakes between large ones) and the quantities determining these transitions.1∕6 0 for small repeaters on the San Andreas fa...

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“…Uchida and Matsuzawa, 2013). These observations may be due to the erosion of coupled asperities by creep processes that have been shown in rate-and-state simulations (Mavrommatis et al, 2017;Jiang and Lapusta, 2017). The large acceleration of aseismic processes in the postseismic stage (Perfettini et al, 2010) then evokes a higher rate of microseismicity in these mostly creeping regions, which allows the clear identification of such separators close to the main shock area during aftershock series.…”

Section: Mogi Doughnuts and The Temporal Evolution Of Seismicity Pattmentioning

confidence: 81%

Microseismicity appears to outline highly coupled regions on the Central Chile megathrust

Sippl¹,

Moreno²,

Benavente³

2022

Preprint

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We compiled a novel microseismicity catalog for the Central Chile megathrust (29-35◦S), comprising 8750 earthquakes between 04/2014 and 12/2018. These events describe a pattern of three trenchward open half-ellipses, consisting of a continuous, coast-parallel seismicity band at 30-45 km depth, and narrow elongated seismicity clusters that protrude to the shallow megathrust and separate largely aseismic regions along strike. To test whether these shapes could outline highly coupled regions (“asperities”) on the megathrust, we invert GPS displacement data for interplate locking. The best-ﬁt locking model does not show good correspondence to seismicity, possibly due to lacking resolution. When we prescribe high locking inside the half-ellipses, however, we obtain models with similar data ﬁts that are preferred according to the Bayesian Information Criterion (BIC). We thus propose that seismicity on the Central Chile megathrust may outline three adjacent highly coupled regions, two of them located between the rupture areas of the 2010 Maule and the 2015 Illapel earthquakes, a segment of the Chilean margin that may be in a late interseismic stage of the seismic cycle.

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A Physical Model for Interseismic Erosion of Locked Fault Asperities

Cited by 18 publications

References 59 publications

Forming a Mogi Doughnut in the Years Prior to and Immediately Before the 2014 M8.1 Iquique, Northern Chile, Earthquake

Forming a Mogi Doughnut in the Years Prior to and Immediately Before the 2014 M8.1 Iquique, Northern Chile, Earthquake

Crack Models of Repeating Earthquakes Predict Observed Moment‐Recurrence Scaling

Microseismicity appears to outline highly coupled regions on the Central Chile megathrust

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