scholarly journals An Explanation of Episodic Tremor and Slow Slip Constrained by Crack‐Seal Veins and Viscous Shear in Subduction Mélange

2018 ◽  
Vol 45 (11) ◽  
pp. 5371-5379 ◽  
Author(s):  
Kohtaro Ujiie ◽  
Hanae Saishu ◽  
Åke Fagereng ◽  
Naoki Nishiyama ◽  
Makoto Otsubo ◽  
...  
Keyword(s):  
Slow Slip ◽  
Viscous Shear ◽  
Episodic Tremor

scholarly journals Length scales and types of heterogeneities along the deep subduction interface: Insights from exhumed rocks on Syros Island, Greece

Geosphere ◽  
2019 ◽  
Vol 15 (4) ◽  
pp. 1038-1065 ◽  
Author(s):  
Alissa J. Kotowski ◽  
Whitney M. Behr
Keyword(s):  
Shear Zone ◽  
Oceanic Crust ◽  
Subduction Zones ◽  
Greenschist Facies ◽  
Coarse Grained ◽  
Slow Slip ◽  
Length Scales ◽  
Viscous Shear ◽  
The Matrix ◽  
Episodic Tremor

Abstract We use structural and microstructural observations from exhumed subduction-related rocks exposed on Syros Island (Cyclades, Greece) to provide constraints on the length scales and types of heterogeneities that occupy the deep subduction interface, with possible implications for episodic tremor and slow slip. We selected three Syros localities that represent different oceanic protoliths and deformation conditions within a subduction interface shear zone, including: (1) prograde subduction of oceanic crust to eclogite facies; (2) exhumation of oceanic crust from eclogite through blueschist-greenschist facies; and (3) exhumation of mixed mafic crust and sediments from eclogite through blueschist-greenschist facies. All three localities preserve rheological heterogeneities that reflect metamorphism of primary lithological, geochemical, and/or textural variations in the subducted protoliths and that take the form of brittle pods and lenses within a viscous matrix. Microstructural observations indicate that the matrix lithologies (blueschists and quartz-rich metasediments) deformed by distributed power-law viscous flow accommodated by dislocation creep in multiple mineral phases. We estimate bulk shear zone viscosities ranging from ∼1018 to 1020 Pa-s, depending on the relative proportion of sediments to (partially eclogitized) oceanic crust. Eclogite and coarse-grained blueschist heterogeneities within the matrix preserve multiple generations of dilational shear fractures and veins formed under high-pressure conditions. The veins commonly show coeval or overprinting viscous shear, suggesting repeated cycles of frictional and viscous strain. These geologic observations are consistent with a mechanical model of episodic tremor and slow slip (ETS), in which the deep subduction interface is a rheologically heterogeneous distributed shear zone comprising transiently brittle (potentially tremor-genic) sub-patches within a larger, viscously creeping interface patch. Based on our observations of outcrop and map areas of heterogeneous patches and the sizes, distributions, and amounts of brittle offset recorded by heterogeneities, we estimate that simultaneous brittle failure of heterogeneities could produce tremor bursts with equivalent seismic moments of 4.5 × 109–4.7 × 1014 N m, consistent with seismic moments estimated from geophysical data at active subduction zones.

Hydration- and dehydration-induced rheological heterogeneities on the deep subduction interface, and possible relationships to episodic tremor and slow slip

2020 ◽  
Author(s):  
Whitney Behr ◽  
Carolyn Tewksbury-Christle ◽  
Alissa Kotowski ◽  
Claudio Cannizzaro ◽  
Robert Blass ◽  
...  
Keyword(s):  
Subduction Zones ◽  
Shear Zones ◽  
Ductile Deformation ◽  
Coarse Grained ◽  
Slow Slip ◽  
Brittle Deformation ◽  
Interface Shear ◽  
Dehydration Reactions ◽  
Viscous Shear ◽  
Episodic Tremor

<p>Episodic tremor and slow slip (ETS) is observed in several subduction zones down-dip of the locked megathrust, and may provide clues for preparatory processes before megathrust rupture. Exhumed rocks provide a unique opportunity to evaluate the sources of rheological heterogeneity on the subduction interface and their potential role in generating ETS-like behavior. We present data from two subduction interface shear zones representative of the down-dip extent of the megathrust: the Condrey Mountain Schist (CMS) in northern CA (greenschist to blueschist facies conditions) and the Cycladic Blueschist Unit (CBU) on Syros Island, Greece (blueschist to eclogite facies). Both complexes highlight the propensity for fluid-mediated metamorphic reactions to produce strong rheological heterogeneities:</p><p>In the CMW, hydration reactions led to progressive serpentinization of peridotite bodies that were entrained from the overriding plate and underplated along with oceanic-affinity sediments. The margins of each peridotite-serpentinite lens show extreme strain localization accommodated by dislocation glide and minor pressure solution in antigorite, whereas lens interiors show evidence for more distributed, alternating, frictional-viscous deformation, with abundant crack-seal veins occupied by antigorite, brucite and oxides that are in some places also ductilely sheared. Deformation in the surrounding metasedimentary matrix was purely viscous.</p><p>In the CBU on Syros Island, dehydration reactions in MORB-affinity basalts, subducted and underplated with oceanic and continental-affinity sediments, led to progressive development of strong eclogitic lenses within a weaker blueschist and metasedimentary matrix. The eclogite lenses are commonly coarse-grained and massive and show brittle deformation in the form of dilational and shear fractures/veins filled with quartz, white mica, glaucophane and/or chlorite. Brittle deformation in the eclogites is coeval with ductile deformation in the surrounding blueschist and metasedimentary matrix, indicating concurrent frictional-viscous flow.</p><p>Although we cannot easily distinguish transient deformation processes in exhumed rocks, we can use the following three approaches to assess whether these heterogeneities could have generated deformation behaviors similar to deep ETS: 1) We measure displacements within, and dimensions of the heterogeneities in outcrop/map-scale to estimate the maximum possible seismic moment that would be released when the frictional heterogeneities slip;  2) We compare deformation mechanisms inferred from field and microstructural observations to their expected mechanical behavior from rock deformation experiments; and 3) We use seismo-thermo-mechanical modeling to examine expected slip velocities and moment-duration ratios for frictional-viscous shear zones that are scaled to observations from nature and the lab.  </p><p>All three approaches suggest that frictional-viscous heterogeneities of the types and length-scales we observe in the exhumed rock record are compatible with ETS as documented in modern subduction zones.</p>

scholarly journals Detection of Deep Low-frequency Earthquakes in the Nankai Subduction Zoneover 11 Years Usingamatched Filter Technique

2020 ◽  
Author(s):  
Aitaro Kato ◽  
Shigeki Nakagawa
Keyword(s):  
Matched Filter ◽  
Low Frequency ◽  
Slow Slip ◽  
Slow Slip Events ◽  
Filter Technique ◽  
Strike Direction ◽  
Episodic Tremor And Slip ◽  
Spatio Temporal ◽  
Episodic Tremor

Abstract To improve our understanding of the long-term behavior of low-frequency earthquakes (LFEs) along the tremor belt of the Nankai subduction zone, we applied a matched filter technique to continuous seismic data recorded by a dense and highly sensitive seismic network over an 11year window, April 2004 to August 2015. We detected a total of ~510,000 LFEs, or ~23× the number of LFEs in the JMA catalog for the same period. During long-term slow slip events (SSEs) in the Bungo Channel, a series of migrating LFEbursts intermittently occurred along the fault-strike direction, with slow hypocenter propagation. Elastic energy released by long-term SSEs appears to control the extent of LFE activity. We identify slowlymigrating fronts of LFEs during major episodic tremor and slip (ETS)events, which extend over distances of up to 100 km and follow diffusion-like patterns of spatial evolution with a diffusion coefficient of ~104 m2/s. This migration pattern closely matches the spatio-temporal evolution of tectonictremors reported by previous studies. At shorter distances, up to 15 km, we discovered rapid diffusion-like migrationof LFEs with a coefficient of ~105 m2/s. We also recognize that rapid migration of LFEs occurred intermittently in many streaks during major ETS episodes. These observations suggest that slow slip transients contain a multitude of smaller, temporally clustered fault slip events whose evolution is controlled by a diffusional process.

scholarly journals Slow slip events in the roots of the San Andreas fault

2019 ◽  
Vol 5 (2) ◽  
pp. eaav3274 ◽  
Author(s):  
Baptiste Rousset ◽  
Roland Bürgmann ◽  
Michel Campillo
Keyword(s):  
Global Positioning System ◽  
San Andreas Fault ◽  
Slow Slip ◽  
Slow Slip Events ◽  
San Andreas ◽  
Global Positioning ◽  
The Moment ◽  
Episodic Tremor ◽  
Seismic Signature

Episodic tremor and accompanying slow slip are observed at the down-dip edge of subduction seismogenic zones. While tremors are the seismic signature of this phenomenon, they correspond to a small fraction of the moment released; thus, the associated fault slip can be quantified only by geodetic observations. On continental strike-slip faults, tremors have been observed in the roots of the Parkfield segment of the San Andreas fault. However, associated transient aseismic slip has never been detected. By making use of the timing of transient tremor activity and the dense Parkfield-area global positioning system network, we can detect deep slow slip events (SSEs) at 16-km depth on the Parkfield segment with an average moment equivalent toMw4.90 ± 0.08. Characterization of transient SSEs below the Parkfield locked asperity, at the transition with the creeping section of the San Andreas fault, provides new constraints on the seismic cycle in this region.

scholarly journals Characteristic activity and migration of episodic tremor and slow-slip events in central Japan

2009 ◽  
Vol 61 (7) ◽  
pp. 853-862 ◽  
Author(s):  
Kazushige Obara ◽  
Shutaro Sekine
Keyword(s):  
Slow Slip ◽  
Central Japan ◽  
Slow Slip Events ◽  
And Migration ◽  
Episodic Tremor

Great earthquakes on Canada’s west coast: a review This article is one of a series of papers published in this Special Issue on the theme Lithoprobe — parameters, processes, and the evolution of a continent. Geological Survey of Canada Contribution 20090196.

2010 ◽  
Vol 47 (5) ◽  
pp. 801-820 ◽  
Author(s):  
Roy D. Hyndman ◽  
Garry C. Rogers
Keyword(s):  
Elastic Strain ◽  
Coastal Region ◽  
Vancouver Island ◽  
Cascadia Subduction Zone ◽  
Slow Slip ◽  
Coastal Cities ◽  
Great Earthquakes ◽  
Multidisciplinary Data ◽  
Episodic Tremor And Slip ◽  
Episodic Tremor

The first Lithoprobe transect in 1984 across Vancouver Island had primary objectives to define the structure associated with subduction and constraints on the potential for great thrust earthquakes. The Lithoprobe results and the comprehensive multidisciplinary data collection and analyses that followed provide compelling evidence for past great earthquakes along the Cascadia subduction zone from Vancouver Island to northernmost California, and for present elastic strain build up toward future great events. There is evidence of sudden coastal subsidence up to 2 m and of deep-sea turbidite deposits indicating strong shaking from huge earthquakes at irregular intervals averaging about 500 years, the last in 1700. Precision geodetic measurements define the present buckling of the coastal region, diagnostic of elastic strain accumulation on a locked thrust fault. The landward extent of rupture and, therefore, shaking at coastal cities is constrained by (i) the pattern of elastic strain buildup, (ii) the estimated temperatures on the fault, (iii) the updip limit of episodic tremor and slip (ETS), (iv) the downdip change in reflection character of the thrust, and (v) the magnitude of coastal subsidence in the most recent, 1700, and previous great events. The major earthquakes are very large, M9, rupturing most of the Cascadia margin, but mainly offshore, limiting somewhat the shaking at inland cities but producing large tsunamis. The ETS that occurs at intervals of just over a year appears to involve slow slip on the subduction thrust downdip of the rupture zone that increases stress on the locked zone and may indicate time varying potential for great events.

scholarly journals What’s down there? The structures, materials and environment of deep-seated slow slip and tremor

2021 ◽  
Vol 379 (2193) ◽  
pp. 20200218 ◽  
Author(s):  
Whitney M. Behr ◽  
Roland Bürgmann
Keyword(s):  
Subduction Zones ◽  
Source Region ◽  
Fluid Pressure ◽  
Plate Boundary ◽  
Seismogenic Zone ◽  
Slow Slip ◽  
Earthquake Dynamics ◽  
Plate Interface ◽  
Viscous Shear ◽  
Geophysical Imaging

Deep-seated slow slip and tremor (SST), including slow slip events, episodic tremor and slip, and low-frequency earthquakes, occur downdip of the seismogenic zone of numerous subduction megathrusts and plate boundary strike-slip faults. These events represent a fascinating and perplexing mode of fault failure that has greatly broadened our view of earthquake dynamics. In this contribution, we review constraints on SST deformation processes from both geophysical observations of active subduction zones and geological observations of exhumed field analogues. We first provide an overview of what has been learned about the environment, kinematics and dynamics of SST from geodetic and seismologic data. We then describe the materials, deformation mechanisms, and metamorphic and fluid pressure conditions that characterize exhumed rocks from SST source depths. Both the geophysical and geological records strongly suggest the importance of a fluid-rich and high fluid pressure habitat for the SST source region. Additionally, transient deformation features preserved in the rock record, involving combined frictional-viscous shear in regions of mixed lithology and near-lithostatic fluid pressures, may scale with the tremor component of SST. While several open questions remain, it is clear that improved constraints on the materials, environment, structure, and conditions of the plate interface from geophysical imaging and geologic observations will enhance model representations of the boundary conditions and geometry of the SST deformation process. This article is part of a discussion meeting issue ‘Understanding earthquakes using the geological record’.

Episodic tremor and slow slip potentially linked to permeability contrasts at the Moho

2012 ◽  
Vol 5 (10) ◽  
pp. 731-734 ◽  
Author(s):  
Ikuo Katayama ◽  
Tatsuya Terada ◽  
Keishi Okazaki ◽  
Wataru Tanikawa
Keyword(s):  
Slow Slip ◽  
Episodic Tremor
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