The stress shadow problem in physics-based aftershock forecasting: Does incorporation of secondary stress changes help?

Segou, Margarita; Parsons, Tom

doi:10.1002/2013gl058744

Cited by 10 publications

(13 citation statements)

References 40 publications

(52 reference statements)

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“…The response of the −ΔCFS seismicity in Region III (Figure h) is especially enigmatic: it shows an immediate increase at the time of the Ocotillo event, inconsistent with the simple CFS predictions, although this elevated rate then drops below the pre‐Ocotillo Omori prediction some 20 days after Ocotillo, which is indicative of a delayed stress shadow effect. These results suggest that considering individual receiver focal mechanisms does not improve our ability to evaluate the relationship between static stress and seismicity, which is consistent with previous studies (Cattania et al, ; Meier et al, ; Segou & Parsons, ).…”

Section: Coulomb Stress Modelingsupporting

confidence: 90%

Delayed Seismicity Rate Changes Controlled by Static Stress Transfer

et al. 2017

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On 15 June 2010, a Mw5.7 earthquake occurred near Ocotillo, California, in the Yuha Desert. This event was the largest aftershock of the 4 April 2010 Mw7.2 El Mayor‐Cucapah (EMC) earthquake in this region. The EMC mainshock and subsequent Ocotillo aftershock provide an opportunity to test the Coulomb failure hypothesis (CFS). We explore the spatiotemporal correlation between seismicity rate changes and regions of positive and negative CFS change imparted by the Ocotillo event. Based on simple CFS calculations we divide the Yuha Desert into three subregions, one triggering zone and two stress shadow zones. We find the nominal triggering zone displays immediate triggering, one stress shadowed region experiences immediate quiescence, and the other nominal stress shadow undergoes an immediate rate increase followed by a delayed shutdown. We quantitatively model the spatiotemporal variation of earthquake rates by combining calculations of CFS change with the rate‐state earthquake rate formulation of Dieterich (1994), assuming that each subregion contains a mixture of nucleation sources that experienced a CFS change of differing signs. Our modeling reproduces the observations, including the observed delay in the stress shadow effect in the third region following the Ocotillo aftershock. The delayed shadow effect occurs because of intrinsic differences in the amplitude of the rate response to positive and negative stress changes and the time constants for return to background rates for the two populations. We find that rate‐state models of time‐dependent earthquake rates are in good agreement with the observed rates and thus explain the complex spatiotemporal patterns of seismicity.

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Section: Coulomb Stress Modelingsupporting

confidence: 90%

Delayed Seismicity Rate Changes Controlled by Static Stress Transfer

et al. 2017

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“…Modeling stresses from aftershocks is particularly challenging, since slip distributions or even focal planes are not always known. In fact, Meier et al [] found that including ΔCFS from aftershocks decreases the predictive power of the Coulomb hypothesis, and Segou and Parsons [] found a negligible improvement in predictability. The difference between these results and the improvement in performance in our models may be due to the fact that for most of the events, we assumed an isotropic stress field instead of the full stress field from the focal mechanism.…”

Section: Discussion and Further Analysismentioning

confidence: 99%

Aftershock triggering by postseismic stresses: A study based on Coulomb rate‐and‐state models

et al. 2015

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The spatiotemporal clustering of earthquakes is a feature of medium‐ and short‐term seismicity, indicating that earthquakes interact. However, controversy exists about the physical mechanism behind aftershock triggering: static stress transfer and reloading by postseismic processes have been proposed as explanations. In this work, we use a Coulomb rate‐and‐state model to study the role of coseismic and postseismic stress changes on aftershocks and focus on two processes: creep on the main shock fault plane (afterslip) and secondary aftershock triggering by previous aftershocks. We model the seismic response to Coulomb stress changes using the Dieterich constitutive law and focus on two events: the Parkfield, Mw = 6.0, and the Tohoku, Mw = 9.0, earthquakes. We find that modeling secondary triggering systematically improves the maximum log likelihood fit of the sequences. The effect of afterslip is more subtle and difficult to assess for near‐fault events, where model errors are largest. More robust conclusions can be drawn for off‐fault aftershocks: following the Tohoku earthquake, afterslip promotes shallow crustal seismicity in the Fukushima region. Simple geometrical considerations indicate that afterslip‐induced stress changes may have been significant on trench parallel crustal fault systems following several of the largest recorded subduction earthquakes. Moreover, the time dependence of afterslip strongly enhances its triggering potential: seismicity triggered by an instantaneous stress change decays more quickly than seismicity triggered by gradual loading, and as a result we find afterslip to be particularly important between few weeks and few months after the main shock.

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“…When employing equation to evaluate seismicity rate, a common difficulty is that events may occur in the stress shadow of previous events, where Δ S may be very low, and hence, from equations and , γ may be extremely large [e.g., Segou and Parsons , ; Cattania et al , ]. Very large model γ , and hence low R , evaluated in a shadow zone will generally persist well beyond the early postseismic period.…”

Section: Application To Southern California Seismicitymentioning

confidence: 99%

“…Previous studies have shown that stress shadows are drastically reduced in rate and state when considering small‐scale (unresolved) heterogeneity in the stress field [ Marsan , ; Helmstetter and Shaw , ; Cattania et al , ]. Therefore, the presence of predicted strong stress shadows, and consequently unrealistically low predicted seismicity rates, reflects to a large extent uncertainty in the source models plus the ignorance of other physics that may promote triggering in a shadow of a main shock, e.g., secondary stress changes on nearby faults [ Segou and Parsons , ]. To circumvent this problem, we introduce smoothing of the reciprocal of the state variable, γ −1 .…”

Section: Application To Southern California Seismicitymentioning

confidence: 99%

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Connecting crustal seismicity and earthquake‐driven stress evolution in Southern California

Pollitz

Cattania

2017

JGR Solid Earth

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Tectonic stress in the crust evolves during a seismic cycle, with slow stress accumulation over interseismic periods, episodic stress steps at the time of earthquakes, and transient stress readjustment during a postseismic period that may last months to years. Static stress transfer to surrounding faults has been well documented to alter regional seismicity rates over both short and long time scales. While static stress transfer is instantaneous and long lived, postseismic stress transfer driven by viscoelastic relaxation of the ductile lower crust and mantle leads to additional, slowly varying stress perturbations. Both processes may be tested by comparing a decade‐long record of regional seismicity to predicted time‐dependent seismicity rates based on a stress evolution model that includes viscoelastic stress transfer. Here we explore crustal stress evolution arising from the seismic cycle in Southern California from 1981 to 2014 using five M≥6.5 source quakes: the M7.3 1992 Landers, M6.5 1992 Big Bear, M6.7 1994 Big Bear, M7.1 1999 Hector Mine, and M7.2 2010 El Mayor‐Cucapah earthquakes. We relate the stress readjustment in the surrounding crust generated by each quake to regional seismicity using rate‐and‐state friction theory. Using a log likelihood approach, we quantify the potential to trigger seismicity of both static and viscoelastic stress transfer, finding that both processes have systematically shaped the spatial pattern of Southern California seismicity since 1992.

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The stress shadow problem in physics-based aftershock forecasting: Does incorporation of secondary stress changes help?

Cited by 10 publications

References 40 publications

Delayed Seismicity Rate Changes Controlled by Static Stress Transfer

Delayed Seismicity Rate Changes Controlled by Static Stress Transfer

Aftershock triggering by postseismic stresses: A study based on Coulomb rate‐and‐state models

Connecting crustal seismicity and earthquake‐driven stress evolution in Southern California

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