Stress on the seismogenic and deep creep plate interface during the earthquake cycle in subduction zones

Predicting the spatial extent of mega-earthquakes is an essential ingredient of earthquake hazard assessment. In subduction zones, this prediction mostly relies on geodetic observations of interseismic coupling. However, such models face spatial resolution issues and are of little help to predict full or partial ruptures of highly locked patches. Coupling models are interpreted in the framework of the rate-and-state friction laws. However, these models are too idealized to take into account the effects of a geometrically or rheologically complex plate interface. In this study, we show, from the critical taper theory and a mechanical analysis of the topography, that all recent mega-earthquakes of the Chilean subduction zone are surrounded by distributed interplate deformation emanating from either underplating or basal erosion. This long-lived plate interface deformation builds up stresses ultimately leading to earthquake nucleation. Earthquakes then propagate along a relatively smooth surface and are stopped by segments of heterogeneously distributed deformation. Our results are consistent with long-term features of the subduction margin, with observed short-term deformation as well as physical parameters of recovered subducted fragments. They also provide an explanation for the apparent mechanical segmentation of the megathrust, reconciling many seemingly contradictory observations on the short- and long-term deformation. Consequently, we propose that earthquake segmentation relates to the distribution of deformation along the plate interface and that slip deficit patterns reflect the along-dip and along-strike distribution of the plate interface deformation. Topography would therefore mirror plate interface deformation and could serve to improve earthquake rupture prediction.

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What Controls the Seismogenic Plate Interface in Subduction Zones?

Subduction Top to Bottom - Geophysical Monograph Series ◽

10.1029/gm096p0105 ◽

2013 ◽

pp. 105-111 ◽

Cited By ~ 25

Author(s):

Larry J. Ruff ◽

Bart W. Tichelaar

Keyword(s):

Subduction Zones ◽

Plate Interface

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On the cause of enhanced landward motion of the overriding plate after a major subduction earthquake

10.5194/egusphere-egu2020-18250 ◽

2020 ◽

Author(s):

Mario D'Acquisto ◽

Matthew Herman ◽

Rob Govers

Keyword(s):

Subduction Zones ◽

Relaxation Times ◽

Underlying Mechanism ◽

Rupture Zone ◽

Elastic Response ◽

Postseismic Deformation ◽

Plate Interface ◽

Mechanical Coupling ◽

Megathrust Earthquakes ◽

Viscous Relaxation

<div> During and after a large megathrust earthquake, the overriding plate above the rupture zone moves oceanward. Enigmatically, the post-seismic motion of the overriding plate after several recent large earthquakes, further along strike from the rupture zone, was faster in the landward direction than before the event. Previous studies interpreted these changes as the result of increased mechanical coupling along the megathrust interface, transient slab acceleration, or bulk postseismic deformation with elastic bending mentioned as a possible underlying mechanism. Before invoking additional mechanisms, it is important to understand the contribution of postseismic deformation processes that are inherent features of megathrust earthquakes. We thus aim to quantify and analyse the deformation that produces landward motion during afterslip and viscous relaxation.&#160; </div><div> We use velocity-driven 3D mechanical finite element models, in which large megathrust earthquakes occur periodically on the finite plate interface. The model geometry is similar to most present-day subduction zones, but does not exactly match any specific subduction zone.&#160; </div><div> The results show increased post-seismic landward motion at (trench-parallel) distances greater than 450 km from the middle of the ruptured asperity. Similar patterns of landward motion are generated by viscous relaxation in the mantle wedge and by deep afterslip on the shear zone downdip of the brittle megathrust interface. Landward displacement due to postseismic relaxation largely accumulates at exponentially decaying rates until ~6 Maxwell relaxation times after the earthquake. The spatial distribution and magnitude of the velocity changes is broadly consistent with observations related to both the 2010 Maule and the 2011 Tohoku-oki earthquakes.&#160;&#160; </div><div> Further model experiments show that patterns of landward motion due to afterslip and to viscous relaxation are insensitive to the locking pattern of the megathrust. However, the locking distribution does affect the magnitudes of the displacements and velocities. Results show that the increased landward displacement due to postseismic deformation scales directly proportionally to seismic moment.&#160; </div><div> We conclude that the landward motion results from in-plane horizontal bending of the overriding plate and mantle. This bending is an elastic response to oceanward tractions near the base of the plate around the ruptured asperity, causing extension locally and compression further away along-trench. This elastic in-plate bending consistently contributes to earthquake-associated changes in surface velocities for the biggest megathrust earthquakes, producing landward motion along strike from the rupture zone. </div>

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Plate speeds modulated by sediment subduction: insights from numerical models

10.5194/egusphere-egu2020-6508 ◽

2020 ◽

Author(s):

Whitney Behr ◽

Adam Holt ◽

Thorsten Becker ◽

Claudio Faccenna

Keyword(s):

Subduction Zones ◽

Convergence Rates ◽

Numerical Models ◽

Finite Width ◽

Dynamic Topography ◽

Plate Interface ◽

Interface Models ◽

Low Viscosity ◽

Uniform Interface ◽

Sinking Velocities

Tectonic plate velocities predominantly result from a balance between the potential energy change of the subducting slab and viscous dissipation in the mantle, bending lithosphere, and slab&#8211;upper plate interface. A range of observations suggest that slabs may be weak, implying a more prominent role for plate interface dissipation than previously thought. Behr & Becker (2018) suggested that the deep interface viscosity in subduction zones should be strongly affected by the relative proportions of sedimentary to mafic rocks that are subducted to depth, and that sediment subduction should thus facilitate faster subduction plate speeds. Here we use fully dynamic 2D subduction models built with the code ASPECT to quantitatively explore how subduction interface viscosity influences: a) subducting plate sinking velocities, b) trench migration rates, c) convergence velocities, d) upper plate strain regimes, e) dynamic topography, and f) interactions with the 660 km mantle transition zone.&#160; We implement two main types of models, including 1) uniform interface models where interface viscosity and slab strength are systematically varied, and 2) varying interface models where a low viscosity sediment strip of finite width is embedded within a higher viscosity interface. Uniform interface models indicate that low viscosity (sediment-lubricated) slabs have substantially faster sinking velocities prior to reaching the 660, especially for weak slabs, and also that they achieve faster &#8216;steady state&#8217; velocities after 660 penetration. Even models where sediments are limited to a strip on the seafloor show accelerations in convergence rates of up to ~5 mm/y per my, with convergence initially accommodated by trench rollback and later by slab sinking. We discuss these results in the context of well-documented plate accelerations in Earth&#8217;s history such as India-Asia convergence and convergence rate oscillations along the Andean margin.References: Behr, W. M., & Becker, T. W. (2018). Sediment control on subduction plate speeds. Earth and Planetary Science Letters,&#160;502, 166-173.

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Afterslip and slow slip events in the postseismic deformation of the 2016 Pedernales earthquake, Ecuador

10.5194/egusphere-egu2020-6777 ◽

2020 ◽

Author(s):

Frederique Rolandone ◽

Jean-Mathieu nocquet ◽

Patricia Mothes ◽

Paul Jarrin ◽

Mathilde Vergnolle

Keyword(s):

Subduction Zones ◽

Postseismic Deformation ◽

Slow Slip ◽

Aseismic Slip ◽

Plate Interface ◽

Slow Slip Events ◽

North East ◽

Rupture Area ◽

Slip Event ◽

Seismic Swarms

In subduction zones, slip along the plate interface occurs in various modes including earthquakes, steady slip, and transient accelerated aseismic slip during either Slow Slip Events (SSE) or afterslip. We analyze continuous GPS measurements along the central Ecuador subduction segment to illuminate how the different slip modes are organized in space and time in the zone of the 2016 Mw 7.8 Pedernales earthquake. The early post-seismic period (1 month after the earthquake) shows large and rapid afterslip developing at discrete areas of the megathrust and a slow slip event remotely triggered (&#8764;100 km) south of the rupture of the Pedernales earthquake. We find that areas of large and rapid early afterslip correlate with areas of the subduction interface that had hosted SSEs in years prior to the 2016 earthquake. Areas along the Ecuadorian margin hosting regular SSEs and large afterslip had a dominant aseismic slip mode that persisted throughout the earthquake cycle during several years and decades: they regularly experienced SSEs during the interseismic phase, they did not rupture during the 2016 Pedernales earthquake, they had large aseismic slip after it. Four years after the Pedernales earthquake, postseismic deformation is still on-going. Afterslip and SSEs are both involved in the postseimsic deformation. Two large aftershocks (Mw 6.7 & 6.8) occurred after the first month of postseismic deformation in May 18, and later in July 7 2016 two other large aftershocks (Mw 5.9 & 6.3) occurred, all were located north east of the rupture. They may have triggered their own postseismic deformation. Several seismic swarms were identified south and north of the rupture area by a dense network of seismic stations installed during one year after the Pedernales earthquakes, suggesting the occurrence of SSEs. Geodetically, several SSEs were detected during the postseismic deformation either in areas where no SSEs were detected previously, or in areas where regular seismic swarms and repeating earthquakes were identified. The SSEs may have been triggered by the stress increment due to aftershocks or due to afterslip.

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Warm thermal structures in subduction zones lead to ample dehydration at the depths of deep slow slip and tremor and resultant transformations in viscous rheology

10.5194/egusphere-egu21-13926 ◽

2021 ◽

Author(s):

Cailey Condit ◽

Victor Guevara ◽

Melodie French ◽

Adam Holt ◽

Jonathan Delph

Keyword(s):

Subduction Zones ◽

Thermal Structure ◽

Fluid Pressure ◽

Plate Boundary ◽

Pore Fluid ◽

Seismogenic Zone ◽

Plate Interface ◽

Dehydration Reactions ◽

Episodic Tremor And Slip ◽

Increased Strength

Feedbacks amongst petrologic and mechanical processes along the subduction plate boundary play a central role influencing slip behaviors and deformation styles. Metamorphic reactions, resultant fluid production, deformation mechanisms, and strength are strongly temperature dependent, making the thermal structure of these zones a key control on slip behaviors.&#160;Firstly, we investigate the role of metamorphic devolatilization reactions in the production of Episodic Tremor and Slip (ETS) in warm subduction zones. Geophysical and geologic observations of ETS hosting subduction zones suggest the plate interface is fluid-rich and critically stressed, which together, suggests that this area is a zone of near lithostatic pore fluid pressure. &#160;Fluids and high pore fluid pressures have been invoked in many models for ETS. However, whether these fluids are sourced from local dehydration reactions in particular lithologies, or via up-dip transport from greater depths remains an open question. We present thermodynamic models of the petrologic evolution of four lithologies typical of the plate interface along predicted pressure&#8211;temperature (P-T) paths for the plate boundary along Cascadia, Nankai, and Mexico which all exhibit ETS at depths between 25-65 km. Our models suggest that 1-2 wt% H2O is released at the depths of ETS along these subduction segments due to punctuated dehydration reactions within MORB, primarily through chlorite and/or lawsonite breakdown. These reactions produce sufficient in-situ fluid across this narrow P-T range to cause high pore fluid pressures. Punctuated dehydration of oceanic crust provides the dominant source of fluids at the base of the seismogenic zone in these warm subduction margins, and up-dip migration of fluids from deeper in the subduction zone is not required to produce ETS-facilitating high pore fluid pressures. These dehydration reactions not only produce metamorphic fluids at these depths, but also result in an increased strength of viscous deformation through the breakdown of weak hydrous phases (e.g., chlorite, glaucophane) and the growth of stronger minerals (e.g., garnet, omphacite, Ca-amphibole). Lastly, we present preliminary data on viscosity along warm subduction paths showing the locations of these dehydration pulses correlate with viscosity increases in mafic lithologies along the shallow forarc.

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Fluid-mediated carbon release by infiltration of serpentinite dehydration fluids during subduction: insights from thermodynamic models of serpentinite-hosted carbonate rocks

10.5194/egusphere-egu2020-11027 ◽

2020 ◽

Author(s):

Manuel Menzel ◽

Carlos J. Garrido ◽

Vicente López Sánchez Vizcaíno

Keyword(s):

Open System ◽

Carbonate Rocks ◽

Subduction Zones ◽

Carbon Fluxes ◽

Oceanic Lithosphere ◽

Chemical System ◽

Fluid Composition ◽

Plate Interface ◽

Carbon Solubility ◽

Carbon Release

Serpentinites can significantly modulate the carbon fluxes in subduction zones because they occasionally host substantial concentrations of carbonate formed during the oceanic stage of subducting oceanic lithosphere (ophicalcite; [1]) or during metasomatic reaction with CO2-bearing fluids at the subduction plate interface (e.g. hybrid carbonate&#8211;talc rocks; [2]). At subarc depth, fluid-mediated carbon release from lithologies like serpentinite-hosted carbonates is critical to understand the global carbon balance and magnitude of carbon fluxes from the subducting plate into the deep mantle. However, the solubility of carbon and the open-system metasomatic reactions during fluid-rock interactions in carbonated serpentinites at high P are not fully understood. In line with previous studies of prograde devolatilization [3], newer models show that the carbon release during prograde devolatilization reactions of serpentinite-hosted carbonate rocks is limited even if accounting for the higher carbon solubility of electrolytic fluids compared to molecular fluid models [4]. Therefore, devolatilization reactions driven by infiltration of Atg-serpentinite dehydration fluids into serpentinite-hosted meta-carbonate rocks determines how much carbon in the mantle lithosphere subducts deep into the mantle. Here we present the results of thermodynamic modelling &#8211; using the implementation of the DEW aqueous database in Perple_X [5] &#8211; to explore subduction fluid compositions and metasomatism of serpentinite-hosted carbonate rocks during prograde and infiltration-driven devolatilization reactions. The chemical system of serpentinite + carbonate is ideal to understand the interplay of changes in fluid composition, pH, bulk chemical modification and mineral assemblage during open-system fluid infiltration metamorphism. Our models provide new insights into the interaction of carbon-bearing subduction fluids with the cold hydrated mantle wedge, and the carbon release from serpentinite-hosted carbonates related to infiltration of serpentinite dehydration fluids at subarc depths. Our results further show that even though high fluid fluxes from serpentinite dehydration will transform meta-ophicalcites and talc-carbonate rocks into carbonate-garnet-clinopyroxene-olivine rocks and carbon-bearing orthopyroxenites, these rocks can subduct carbon beyond subarc depths into the deeper mantle where they may be related to the formation of deep diamonds, carbonatites and kimberlites.REFERENCES[1] Menzel et al., 2019, JMG 37, 681&#8211; 715.[2] Spandler et al., 2008, CMP 155, 181-198.[3] Kerrick & Connolly, 1998, Geology 26, 375-378.[4] Menzel et al., 2020, EPSL 531.[5] Connolly & Galvez, 2018, EPSL 501, 90-102.

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Fore-arc building and destruction: a critical interplay between fluid flow, megathrust strength and tectonic underplating

10.5194/egusphere-egu2020-1783 ◽

2020 ◽

Author(s):

Armel Menant ◽

Samuel Angiboust ◽

Taras Gerya ◽

Robin Lacassin ◽

Martine Simoes ◽

...

Keyword(s):

Subduction Zones ◽

Fluid Distribution ◽

Plate Interface ◽

Erosion Processes ◽

Active Margins ◽

Mechanical Models ◽

Mass Transfers ◽

High Topography ◽

Critical Process

Subduction zones are the loci of huge mass transfers, including accretion and erosion processes responsible for the long-term formation (and destruction) of fore-arc margins. Study of now-exhumed deep portions of the fore-arc crust revealed km-scale tectonic units of marine sediments and oceanic crust, which have been underplated (i.e. basally accreted) to the overriding plate. However, geophysical observations of this deep process in active subduction zones are unclear and the dynamics of tectonic underplating, as well as its existence, along most of active margins remain controversial. We attempt to shed light on this critical process from the plate interface where tectonic slicing is triggered, to the surface where topographic variations are expected in response to such a mass transfer.Using high-resolution visco-elasto-plastic thermo-mechanical models, we present with unprecedented details the dynamics of formation, preservation and destruction of underplated crustal nappes at 10-40-km depth in subductions zones. Our results show that subduction segments exhibiting an increasing frictional behaviour control deep accretionary dynamics and that the long-term frictional zonation of the plate interface is stable due to a positive feedback between fluid distribution and effective stress. As a result, discrete underplating events follow one after another for tens of Myr, leading to the formation of a thick duplex structure supporting a coastal topographic high. The rise of this high topography is cadenced by Myr-scale uplift-then-subsidence cycles, characterising each underplating event and the subsequent period of wedge re-equilibration. This periodical evolution is significantly modified by changing the rheological properties of the material entering the subduction zone, suggesting that tectonic underplating is likely a transient process active along most of active margins, depending on severe variations of the hydro-mechanical properties of the plate interface at Myr timescale.

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Kinematics of Subduction Processes during the Earthquake Cycle in Central Chile

Seismological Research Letters ◽

10.1785/0220180391 ◽

2019 ◽

Cited By ~ 1

Author(s):

Leonardo Aguirre ◽

Klaus Bataille ◽

Camila Novoa ◽

Carlos Peña ◽

Felipe Vera

Keyword(s):

Subduction Zones ◽

Slip Rate ◽

Convergent Margins ◽

Earthquake Cycle ◽

Central Chile ◽

The North ◽

The Future ◽

Maule Earthquake ◽

Kinematic Models ◽

Inversion Techniques

ABSTRACT Subduction processes at convergent margins produce complex temporal and spatial crustal displacements during different periods of the earthquake cycle. Satellite geodesy observations provide important clues to constrain kinematic models at subduction zones. Here, we analyze geodetic observations in central Chile, where two large earthquakes occurred: 2010 Mw 8.8 Maule and 2015 Mw 8.3 Illapel. We propose a model that considers the motion along both interfaces of the brittle subducting slab as the sources responsible for the movement of the crust in the different periods of the earthquake cycle. Using standard inversion techniques, we provide a consistent framework of the kinematic displacement during each period of the earthquake cycle. We show that during the interseismic period prior to the Maule and Illapel earthquakes, two patches of slip rate on the lower interface are determined. These patches are located just below the future hypocenters. Because the interseismic period corresponds to the loading process and the coseismic to the unloading process, it is interesting to note that the area where loading is stronger corresponds to the area where unloading is also strong. Furthermore, we show that the Maule earthquake causes a significant displacement on the lower interface, just below the epicenter of the future Illapel earthquake to the north, a few years later. We speculate that the interaction between motions along both interfaces is the key to understanding the evolution of stress and the occurrence of earthquakes at subduction zones. This framework improves the understanding of the observed loading and unloading processes and potential triggering between subduction earthquakes.

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