Effective friction law for small-scale fault heterogeneity in 3D dynamic rupture

Geological observations show variations in fault-surface topography not only at large scale (segmentation) but also at small scale (roughness). These geometrical complexities strongly affect the stress distribution and frictional strength of the fault, and therefore control the earthquake rupture process and resulting ground-shaking. Previous studies examined fault-segmentation effects on ground-shaking, but our understanding of fault-roughness effects on seismic wavefield radiation and earthquake ground-motion is still limited.&#160;&#160;In this study we examine the effects of fault roughness on ground-shaking variability as a function of distance based on 3D dynamic rupture simulations. We consider linear slip-weakening friction, variations of fault-roughness parametrizations, and alternative nucleation positions (unilateral and bilateral ruptures). We use generalized finite difference method to compute synthetic waveforms (max. resolved frequency 5.75 Hz) at numerous surface sites&#160; to carry out statistical analysis.&#160;&#160;Our simulations reveal that ground-motion variability from unilateral ruptures is almost independent of&#160; distance from the fault, with comparable or higher values than estimates from ground-motion prediction equations (e.g., Boore and Atkinson, 2008; Campbell and Bozornia, 2008). However, ground-motion variability from bilateral ruptures decreases with increasing distance, in contrast to previous studies (e.g., Imtiaz et. al., 2015) who observe an increasing trend with distance. Ground-shaking variability from unilateral ruptures is higher than for bilateral ruptures, a feature due to intricate seismic radiation patterns related to fault roughness and hypocenter location. Moreover, ground-shaking variability for rougher faults is lower than for smoother faults. As fault roughness increases the difference in ground-shaking variabilities between unilateral and bilateral ruptures increases. In summary, our simulations help develop a fundamental understanding of ground-motion variability at high frequencies (~ 6 Hz) due small-scale geometrical fault-surface variations.

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Synthetic analysis of seismic back-projection using 3D dynamic rupture simulations of the 2018, Palu Sulawesi earthquake

10.5194/egusphere-egu2020-20703 ◽

2020 ◽

Author(s):

Thomas Ulrich ◽

Bo Li ◽

Alice-Agnes Gabriel

Keyword(s):

Seismic Energy ◽

Fault System ◽

Beam Power ◽

Small Scale ◽

Back Projection ◽

Secondary Phases ◽

Dynamic Rupture ◽

Rupture Dynamics ◽

Projection Techniques ◽

Spatio Temporal

Back-projection uses the time-reversal property of the seismic wavefield recorded at large aperture dense seismic arrays. Seismic energy radiation is imaged by applying array beam-forming techniques. The spatio-temporal rupture complexity of large earthquakes can be imaged simply and rapidly with a limited number of assumptions, which makes back-projection techniques an important tool of modern seismology. However, back-projection analyses exhibit frequency and array dependency (e.g. Wu et al., AGU19). In addition, the method relies on station network geometry and data quality and can suffer from imaging artifacts (e.g., Fan and Shearer, 2017) and back-projection results may not be consistently interpreted.The Mw7.5 Palu, Sulawesi earthquake that occurred on September 28, 2018, ruptured a 180 km long section of the Palu-Koro fault. The earthquake triggered a localized but powerful tsunami within Palu Bay, which swept away houses and buildings. The supershear earthquake and unexpected tsunami led to more than 4000 fatalities. Ulrich et al. (2019) propose a physics-based, coupled earthquake-tsunami scenario of the event, tightly constrained by observations. The model matches key observed earthquake characteristics, including moment magnitude, rupture duration, fault plane solution, teleseismic waveforms, and inferred horizontal ground displacements. It suggests that time-dependent earthquake-induced uplift and subsidence could have sourced the observed tsunami within Palu Bay.Back-projection has been used to track the rupture propagation of the Palu earthquake. Bao et al. (2019) image unilateral rupture traveling at a supershear rupture speed. Their results show array dependent ruptures, from a rather relatively linear rupture using the Australian array, to a spatio-temporally more scattered image using the seismic array in Turkey. In addition, they do not resolve any portion of the rupture as traveling at sub-Rayleigh speeds, while Wei et al. (AGU19) suggest a gradually accelerating rupture.In this study, we build upon the dynamic rupture model of Ulrich et al. (2019) to investigate the reliability of standard back-projection techniques using a realistic and perfectly known earthquake model. In particular, we investigate whether or not rupture transfers across the segmented fault system, and the effect of specific geometric features of the fault system, such as fault bends, on rupture dynamics, leave a clear signal on the inferred beam power. Also, we investigate the effect of secondary phases, such as reflections from the free-surface or from fault segment boundaries, naturally captured by dynamic rupture modeling. In addition, we study the effect of small-scale source heterogeneities on the back-projection results by including different levels of fault roughness in the dynamic rupture simulations. Finally, we investigate the array dependence of back-projection results.Overall, this study should help to better understand which features of rupture dynamics back-projection can capture. Our results are a first step towards fundamental analysis to better understand which features can be captured by back-projection and to provide guidelines for back-projection interpretation.

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Large-Scale FE Simulation of Fault Dynamic Rupture with Slip-Weakening Friction Law

Journal of Applied Mechanics ◽

10.2208/journalam.6.367 ◽

2003 ◽

Vol 6 ◽

pp. 367-375

Author(s):

Jun Yin ◽

Mikio Iizuka ◽

Kazuro Hirahara ◽

Zhishen Wu

Keyword(s):

Large Scale ◽

Fe Simulation ◽

Dynamic Rupture ◽

Friction Law

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Formation of levees, troughs and elevated channels by avalanches on erodible slopes

Journal of Fluid Mechanics ◽

10.1017/jfm.2017.309 ◽

2017 ◽

Vol 823 ◽

pp. 278-315 ◽

Cited By ~ 17

Author(s):

A. N. Edwards ◽

S. Viroulet ◽

B. P. Kokelaar ◽

J. M. N. T. Gray

Keyword(s):

Risk Mitigation ◽

Constant Width ◽

Small Scale ◽

Snow Avalanches ◽

Erosion And Deposition ◽

Friction Law ◽

Slope Inclination ◽

Deposit Surface ◽

Rough Bed ◽

Initial Deposit

Snow avalanches are typically initiated on marginally stable slopes with a surface layer of fresh snow that may easily be incorporated into them. The erosion of snow at the front is fundamental to the dynamics and growth of snow avalanches and they may rapidly bulk up, making them much more destructive than the initial release. Snow may also deposit at the rear, base and sides of the flow and the net balance of erosion and deposition determines whether an avalanche grows or decays. In this paper, small-scale analogue experiments are performed on a rough inclined plane with a static erodible layer of carborundum grains. The static layer is prepared by slowly closing down a flow from a hopper at the top of the slope. This leaves behind a uniform-depth layer of thickness $h_{stop}$ at a given slope inclination. Due to the hysteresis of the rough bed friction law, this layer can then be inclined to higher angles provided that the thickness does not exceed $h_{start}$, which is the maximum depth that can be held static on a rough bed. An avalanche is then initiated on top of the static layer by releasing a fixed volume of carborundum grains. Dependent on the slope inclination and the depth of the static layer three different behaviours are observed. For initial deposit depths above $h_{stop}$, the avalanche rapidly grows in size by progressively entraining more and more grains at the front and sides, and depositing relatively few particles at the base and tail. This leaves behind a trough eroded to a depth below the initial deposit surface and whose maximal areal extent has a triangular shape. Conversely, a release on a shallower slope, with a deposit of thickness $h_{stop}$, leads to net deposition. This time the avalanche leaves behind a levee-flanked channel, the floor of which lies above the level of the initial deposit and narrows downstream. It is also possible to generate avalanches that have a perfect balance between net erosion and deposition. These avalanches propagate perfectly steadily downslope, leaving a constant-width trail with levees flanking a shallow trough cut slightly lower than the initial deposit surface. The cross-section of the trail therefore represents an exact redistribution of the mass reworked from the initial static layer. Granular flow problems involving erosion and deposition are notoriously difficult, because there is no accepted method of modelling the phase transition between static and moving particles. Remarkably, it is shown in this paper that by combining Pouliquen & Forterre’s (J. Fluid Mech., vol. 453, 2002, pp. 133–151) extended friction law with the depth-averaged $\unicode[STIX]{x1D707}(I)$-rheology of Gray & Edwards (J. Fluid Mech., vol. 755, 2014, pp. 503–544) it is possible to develop a two-dimensional shallow-water-like avalanche model that qualitatively captures all of the experimentally observed behaviour. Furthermore, the computed wavespeed, wave peak height and stationary layer thickness, as well as the distance travelled by decaying avalanches, are all in good quantitative agreement with the experiments. This model is therefore likely to have important practical implications for modelling the initiation, growth and decay of snow avalanches for hazard assessment and risk mitigation.

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The influence of heterogeneity on the strength and stability of faults

10.5194/egusphere-egu21-8058 ◽

2021 ◽

Author(s):

Daniel Faulkner ◽

John Bedford ◽

Nadia Lapusta ◽

Valère Lambert

Keyword(s):

Shear Stress ◽

Large Scale ◽

Small Scale ◽

Dynamic Rupture ◽

Slip Rates ◽

Average Shear Stress ◽

Lower Shear ◽

Scale Heterogeneity ◽

Fault Strength ◽

Average Shear

<div>Heterogeneity of fault zones is seen at all scales in nature. It may manifest itself in terms of the variability of material property distribution over the fault, of stress heterogeneity brought about by the history of previous earthquake ruptures, and of fault geometry. In this contribution, we consider the effect on fault strength and stability of small-scale heterogeneity in laboratory experiments and large-scale heterogeneity from numerical dynamic rupture modeling. In model laboratory faults at slow slip rates (0.3 and 3 microns/s), the area occupied by rate-weakening gouge (quartz) versus rate-strengthening gouge (clay) was systematically varied and the results compared with homogenized mixtures of the two gouges. We found that the heterogeneous experimental faults were weaker and less stable than their homogenized counterparts, implying that earthquake nucleation might be promoted by fault zone heterogeneity. In elasto-dynamic numerical simulations of sequences of earthquakes and aseismic slip based on rate and state friction but with enhanced dynamic weakening (EDW) through pore fluid pressurization, uniform material properties on the fault plane are assumed, and heterogeneity spontaneously develops by stress variations along the fault arising from differing histories of motion at points along the fault. In these models, ruptures spontaneously nucleate in favorably prestressed regions. Larger ruptures - that result in greater degrees of EDW - are capable of propagating through areas of lower shear stress that would arrest smaller events. This behavior leads to a relationship between rupture size and the average shear stress over the rupture plane before the earthquake occurs. Faults that host larger events may overall appear to be driven by lower average shear stress and hence appear &#8216;weaker&#8217;. It is clear that the apparent fault strength and stability is difficult to predict from either simple homogeneous gouge experiments, or from scaling up of these results. Heterogeneity at all scales will affect the slip behaviour of faults.</div>

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Spontaneous dynamic rupture modeling of 2017 M 5.4 Pohang, South Korea, earthquake, using the slip-weakening friction law

10.5194/egusphere-egu2020-12490 ◽

2020 ◽

Author(s):

Seok Goo Song ◽

Chang Soo Cho ◽

Geoffrey Ely

Keyword(s):

Stress Drop ◽

High Performance ◽

Slip Model ◽

Dynamic Rupture ◽

Coseismic Slip ◽

Southeastern Part ◽

Friction Law ◽

Initial Nucleation ◽

Dynamic Rupture Model ◽

Rupture Model

An M 5.4 earthquake occurred in the southeastern part of the Korean Peninsula in 2017. It is an oblique thrust event that occurred at a relatively shallow depth (~ 5 km) although it did not create coseismic surface rupture. A coseismic slip model was successfully obtained by inverting the ground displacement field extracted by the InSAR data (Song and Lee, 2019). In this study, we performed spontaneous dynamic rupture modeling using the slip weakening friction law. The static stress drop distribution obtained by the coseismic slip model was used as an input stress field. We adopted high performance computing (HPC) using the parallelized dynamic rupture modeling code (SORD, Support Operator Rupture Dynamics). Although our target event is moderate-sized one, we can successfully produce a spontaneous dynamic rupture model using a relatively small initial nucleation patch (radius ~ 1 km) with a relatively small slip weakening distance (~ 5 cm). Our preliminary results show that the rupture creates an asperity near the initial nucleation zone with approximately 4 MPa stress drop, then propagates obliquely upward both in the northeast and southwest directions. Although we assumed a single planar fault plane in our current rupture modeling, it seems worthwhile to dynamically model the rupture process, including complex fault geometry in following studies. Dynamic rupture modeling for a natural earthquake provides an opportunity to understand the dynamic rupture characteristics of the earthquake, including both stress drop and fracture energy.

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On the effective friction law of a heterogeneous fault

Journal of Geophysical Research Atmospheres ◽

10.1029/2000jb900467 ◽

2001 ◽

Vol 106 (B8) ◽

pp. 16307-16322 ◽

Cited By ~ 32

Author(s):

Michel Campillo ◽

Pascal Favreau ◽

Ioan R. Ionescu ◽

Christophe Voisin

Keyword(s):

Friction Law ◽

Effective Friction

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Reversed-Polarity Secondary Deformation Structures Near Fault Stepovers

Journal of Applied Mechanics ◽

10.1115/1.4006154 ◽

2012 ◽

Vol 79 (3) ◽

Cited By ~ 21

Author(s):

Yehuda Ben-Zion ◽

Thomas K. Rockwell ◽

Zheqiang Shi ◽

Shiqing Xu

Keyword(s):

Opposite Polarity ◽

Small Scale ◽

Field Observations ◽

Dynamic Rupture ◽

Deformation Structures ◽

Secondary Deformation ◽

Earthquake Ruptures ◽

Reversed Polarity ◽

Scale Structures ◽

Symmetric Structures

We study volumetric deformation structures in stepover regions using numerical simulations and field observations, with a focus on small-scale features near the ends of rupture segments that have opposite-polarity from the larger-scale structures that characterize the overall stepover region. The reversed-polarity small-scale structures are interpreted to be generated by arrest phases that start at the barriers and propagate some distance back into the rupture segment. Dynamic rupture propagating as a symmetric bilateral crack produces similar (anti-symmetric) structures at both rupture ends. In contrast, rupture in the form of a predominantly unidirectional pulse produces pronounced reversed-polarity structures only at the fault end in the dominant propagation direction. Several observational examples at different scales from strike-slip faults of the San Andreas system in southern California illustrate the existence of reversed-polarity secondary deformation structures. In the examples shown, relatively-small pressure-ridges are seen only on one side of relatively-large extensional stepovers. This suggests frequent predominantly unidirectional ruptures in at least some of those cases, although multisignal observations are needed to distinguish between different possible mechanisms. The results contribute to the ability of inferring from field observations on persistent behavior of earthquake ruptures associated with individual fault sections.

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Reasons to strike first

Behavioral and Brain Sciences ◽

10.1017/s0140525x19000840 ◽

2019 ◽

Vol 42 ◽

Author(s):

William Buckner ◽

Luke Glowacki

Keyword(s):

Intergroup Conflict ◽

Small Scale

Abstract De Dreu and Gross predict that attackers will have more difficulty winning conflicts than defenders. As their analysis is presumed to capture the dynamics of decentralized conflict, we consider how their framework compares with ethnographic evidence from small-scale societies, as well as chimpanzee patterns of intergroup conflict. In these contexts, attackers have significantly more success in conflict than predicted by De Dreu and Gross's model. We discuss the possible reasons for this disparity.

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Exploring Coronal Structures with SOHO

International Astronomical Union Colloquium ◽

10.1017/s0252921100064915 ◽

2000 ◽

Vol 179 ◽

pp. 403-406

Author(s):

M. Karovska ◽

B. Wood ◽

J. Chen ◽

J. Cook ◽

R. Howard

Keyword(s):

Solar Corona ◽

Image Enhancement ◽

Coronal Mass Ejections ◽

Dynamical Evolution ◽

Small Scale ◽

Low Contrast ◽

Contrast Structures ◽

Scale Structures ◽

Small Scale Structures ◽

Coronal Structures

AbstractWe applied advanced image enhancement techniques to explore in detail the characteristics of the small-scale structures and/or the low contrast structures in several Coronal Mass Ejections (CMEs) observed by SOHO. We highlight here the results from our studies of the morphology and dynamical evolution of CME structures in the solar corona using two instruments on board SOHO: LASCO and EIT.

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