Characteristics of secondary slip fronts associated with slow earthquakes in Cascadia

Blétery, Quentin; Thomas, Amanda M.; Hawthorne, J. C.; Skarbek, R.; Rempel, A. W.; Krogstad, R. D.

doi:10.1016/j.epsl.2017.01.046

Cited by 30 publications

(71 citation statements)

References 51 publications

(49 reference statements)

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“…According to the proportionality between tremor migration speed and the background slow slip velocity (Equation 11), this slowdown reflects the spatial distribution of the slip velocity of the SSE pulse. This model feature is consistent with observations by Bletery et al (2017) of a tendency of tremor migration to slow down further behind the SSE front. This suggests that RTR migration speed provides a constraint on the spatial distribution of slip velocity in an SSE, and the distance reached by RTRs constrains the width of an SSE pulse.…”

Section: Rtr Propagation Distance Velocity and Possible Implicationssupporting

confidence: 81%

“…Thus we interpret the very fast (mostly) along-dip tremor swarms as running along the front of the SSE pulse, where the highest V bg values are concentrated, and RTRs as swarms running into the tail of the SSE pulse, where V bg is lower. The slowdown of RTRs (Bletery et al 2017) and tremor branching are interpreted as swarms running further into the SSE pulse tail where V bg gradually decreases.…”

Section: Conceptual Modelsmentioning

confidence: 99%

“…An imbricated hierarchy of tremor migration patterns has been observed in the Cascadia subduction zone (Figure 1) during each recurring episodic tremor and slow-slip event (ETS): large-scale forward tremor propagation along the fault strike direction at about 5-10 km/day, sparsely distributed swarms that propagate about 5 to 50 times faster in the opposite direction ("rapid tremor reversals" or RTRs) (Houston et al 2011), and tremor swarms that propagate even faster along-dip in the vicinity of the main SSE front (Ghosh et al 2010;Peng et al 2015). Bletery et al (2017) found that secondary tremor fronts slow down as they propagate. Other tremor migration patterns have also been observed, such as tremor halting and branching, acceleration and deceleration (Kao et al 2009).…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Preprint: Tremor migration patterns and the collective behavior of deep asperities mediated by creep

Luo¹,

Ampuero²

2017

Preprint

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Slow-slip events (SSE) and non-volcanic tremors have revealed a broad spectrum of earthquake behavior, involving entangled seismic and aseismic slip, and offer a unique window into fault mechanics at the bottom of seismogenic zones. A hierarchy of migration patterns of tremors has been observed in the Cascadia subduction zone, including large-scale along-strike tremor propagation and Rapid Tremor Reversals (RTR) migrating in opposite directions with much higher propagation speeds. Here we show that these tremor migration patterns can be reproduced by two end-member models of a fault with heterogeneous mechanical properties, composed of competent asperities embedded in a more frictionally stable, incompetent matrix. In the SSE-driven-tremor model, SSEs are spontaneously generated by the matrix, even in absence of seismic asperities, and drive tremor. In the tremor-driven-SSE model the matrix is stable, it slips steadily in absence of asperities, and SSEs result from the collective behavior of tremor asperities interacting via transient creep in the form of local afterslip fronts. We study these two end-member models through 2D quasi-dynamic multi-cycle simulations of faults governed by rate-and-state friction with heterogeneous frictional properties and effective normal stress, using the earthquake simulation software QDYN . In both models, tremor migration patterns emerge from interactions between asperities mediated by creep transients. The models successfully reproduce forward tremor propagation and RTRs, as well as various other observed tremor migration patterns, without the need to finely tune model parameters. Our modeling results suggest that, in contrast to a common view, SSE could be a result of tremor activity. Also, the hierarchical pattern of tremor migrations provides general constraints on fault zone rheology, and the location of RTRs and other tremor patterns might shed light on the finer scale spatial variability of fault properties. We also find that, despite important interactions between asperities, tremor activity rates are proportional to the underlying aseismic slip rate, supporting an approach to estimate SSE properties with high spatial-temporal resolutions via tremor activity.

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Section: Rtr Propagation Distance Velocity and Possible Implicationssupporting

confidence: 81%

Section: Conceptual Modelsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Preprint: Tremor migration patterns and the collective behavior of deep asperities mediated by creep

Luo¹,

Ampuero²

2017

Preprint

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“…Bartlow et al, 2014;Bletery et al, 2017;Bostock et al, 2015;Brodsky & Mori, 2007;Hawthorne et al, 2016;Ide et al, 2007;Ito & Obara, 2006; long timescale) Episodic (short timescale) Continuous (short timescale) (a) versus median slip per episode. (b) versus median slip between episodes.…”

mentioning

confidence: 99%

Using Low‐Frequency Earthquake Families on the San Andreas Fault as Deep Creepmeters

et al. 2018

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The central section of the San Andreas Fault hosts tectonic tremor and low‐frequency earthquakes (LFEs) similar to subduction zone environments. LFEs are often interpreted as persistent regions that repeatedly fail during the aseismic shear of the surrounding fault allowing them to be used as creepmeters. We test this idea by using the recurrence intervals of individual LFEs within LFE families to estimate the timing, duration, recurrence interval, slip, and slip rate associated with inferred slow slip events. We formalize the definition of a creepmeter and determine whether this definition is consistent with our observations. We find that episodic families reflect surrounding creep over the interevent time, while the continuous families and the short time scale bursts that occur as part of the episodic families do not. However, when these families are evaluated on time scales longer than the interevent time these events can also be used to meter slip. A straightforward interpretation of episodic families is that they define sections of the fault where slip is distinctly episodic in well‐defined slow slip events that slip 16 times the long‐term rate. In contrast, the frequent short‐term bursts of the continuous and short time scale episodic families likely do not represent individual creep events but rather are persistent asperities that are driven to failure by quasi‐continuous creep on the surrounding fault. Finally, we find that the moment‐duration scaling of our inferred creep events are inconsistent with the proposed linear moment‐duration scaling. However, caution must be exercised when attempting to determine scaling with incomplete knowledge of scale.

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“…It is likely that in some areas, the distribution of pore fluid pressures is close to lithostatic (e.g., Byerlee, 1990;Faulkner & Rutter, 2001;Rice, 1992;Streit & Cox, 2001), taking the form p = gh + C and breaking with the linear depth dependency of c predicted by equation (11). Near-lithostatic pore fluid pressure appears, for instance, to be required to explain the characteristics of slow earthquakes (e.g., Audet & Bürgmann, 2014;Liu & Rice, 2007;Segall et al, 2010) and other slow-slip phenomena (e.g., Bletery et al, 2017;Shelly et al, 2006), in particular their sensitivity to extremely small tidal stress perturbations (Thomas et al, 2009). Such phenomena are well documented in Nankai both at depth and in the wedge (e.g., Nakajima & Hasegawa, 2016;Obara & Kato, 2016;Shelly et al, 2006), implying that the actual shear strength in the Nankai section (contours n ∘ 12 and n ∘ 13 in Figure 4) is probably locally much smaller than suggested in Figure 4.…”

Section: Resultsmentioning

confidence: 99%

Imaging Shear Strength Along Subduction Faults

Blétery

Thomas

Rempel

et al. 2017

Geophysical Research Letters

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Subduction faults accumulate stress during long periods of time and release this stress suddenly, during earthquakes, when it reaches a threshold. This threshold, the shear strength, controls the occurrence and magnitude of earthquakes. We consider a 3‐D model to derive an analytical expression for how the shear strength depends on the fault geometry, the convergence obliquity, frictional properties, and the stress field orientation. We then use estimates of these different parameters in Japan to infer the distribution of shear strength along a subduction fault. We show that the 2011 Mw9.0 Tohoku earthquake ruptured a fault portion characterized by unusually small variations in static shear strength. This observation is consistent with the hypothesis that large earthquakes preferentially rupture regions with relatively homogeneous shear strength. With increasing constraints on the different parameters at play, our approach could, in the future, help identify favorable locations for large earthquakes.

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Characteristics of secondary slip fronts associated with slow earthquakes in Cascadia

Cited by 30 publications

References 51 publications

Preprint: Tremor migration patterns and the collective behavior of deep asperities mediated by creep

Preprint: Tremor migration patterns and the collective behavior of deep asperities mediated by creep

Using Low‐Frequency Earthquake Families on the San Andreas Fault as Deep Creepmeters

Imaging Shear Strength Along Subduction Faults

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