Links between sediment consolidation and Cascadia megathrust slip behaviour

Han, S.; Bangs, N. L.; Carbotte, S. M.; Saffer, D. M.; Gibson, J. C.

doi:10.1038/s41561-017-0007-2

Cited by 67 publications

(146 citation statements)

References 56 publications

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“…Sediment porosity above the plate interface decreases landward by a factor of >3 (from ~30% to <10%) over the 20 km nearest the trench (Figure 5h). A synthetic seismic P wave velocity ( V p ) cross section, constructed using an empirically derived V p ‐porosity relationship that describes marine sediments from several subduction margins (Hoffman & Tobin, 2004) (Figure S3), suggests more than a twofold increase in V p over the same region (Figure 5j), consistent with seismic imaging at multiple margins that documents rapidly increasing V p as a function of distance into the subduction zone, associated with rapid early compaction of porous sediments (e.g., Barnes et al, 2018; Han et al, 2017; Li et al, 2018; Tobin & Saffer, 2009). Patterns of fluid flow, excess pore pressure, and sediment porosity are strongly modulated by the upper plate fault structure that evolves in our model.…”

Section: Resultssupporting

confidence: 62%

“…Nonetheless, the compiled observations and our modeling suggest that, to first order, incoming sediment thickness is one primary control on the state of fluid overpressure at the regional scale (Li et al, 2018; Saffer & Bekins, 2006). The highly variable sediment thickness among global subduction zones ( Scholl et al, 2015) or along strike of individual margins (e.g., Dean et al, 2010 [Sumatra]; Han et al, 2017 [Cascadia]; Barnes et al, 2018 [Hikurangi]; Li et al, 2018 [Alaska]) may hence impact a range of forearc characteristics such as the deformation style of the frontal wedge and shallow megathrust slip behavior, through its modulation of basal fluid pressure, megathrust shear strength, and the degree of sediment consolidation (Ellis et al, 2019; Han et al, 2017; Hüpers et al, 2017; Tobin & Saffer, 2009).…”

Section: Discussionmentioning

confidence: 99%

“…Field and laboratory observations have also documented variations in other parameters, including plate convergence rate (DeMets et al, 2010), slab dip angle (Hayes et al, 2018), and subduction décollement strength (Ikari, 2019; Ikari & Kopf, 2017). Detailed regional studies suggest that some of these subduction zone parameters can even vary substantially over short distances along strike at a single margin, possibly leading to contrasting forearc features including megathrust locking state and slip behavior, wedge morphology and faulting style, and sediment consolidation state (e.g., [Sumatra] Dean et al, 2010; [Cascadia] Han et al, 2017; [Alaska] Li et al, 2018; [Hikurangi] Wallace et al, 2009).…”

Section: Methodsmentioning

confidence: 99%

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Coupled Evolution of Deformation, Pore Fluid Pressure, and Fluid Flow in Shallow Subduction Forearcs

2020

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Deformation and fluid flow in subduction zone forearcs are dynamically coupled, but our quantitative understanding of their coupling is incomplete. In this work, we investigate the hydrological and mechanical coupling in shallow forearcs, using a Lagrangian‐Eulerian finite element model that incorporates constitutive and transport properties of sediments and faults constrained by laboratory and field measurements. Wide‐ranging observations show that sediment thickness and composition, plate convergence rate, basement strength and roughness, and subducting slab dip angle vary between subduction zones. We therefore systematically study their effects on forearc stress and pore fluid pressure states, consolidation and dewatering patterns, and margin morphology. Our models, with the incorporation of a simple description of permeability enhancement along fault damage zones, yield a range of fault permeability (10−13–10−17 m2) consistent with previous estimates and describe the important role of upper plate splay faults in causing heterogeneous dewatering and consolidation patterns and in modulating effective normal stress on the plate interface. Spatial variations in tectonic loading and sediment consolidation can also be caused by subducting basement roughness such as a horst‐and‐graben structure. For typically observed relief and spacing, our models predict locally enhanced porosity reduction by up to 50% at the downdip edge of the horsts and anomalously high sediment porosity above the geometrical highs. At the margin scale, our results demonstrate that sediment permeability and thickness are dominant controls on fluid overpressure, sediment compaction, and megathrust strength. Rough and frictionally strong megathrusts produce similar effects in driving high wedge tapers.

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Section: Resultssupporting

confidence: 62%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Coupled Evolution of Deformation, Pore Fluid Pressure, and Fluid Flow in Shallow Subduction Forearcs

2020

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“…In the northern region (north of 46°N), only 33 earthquakes were detected during the OBS deployment period. Overconsolidated sediments are observed near the deformation front and in the outer wedge, with sediments ≤600 m thick being subducted (Adam et al, 2004;Booth-Rea et al, 2008;Han et al, 2017). This regionally subdued rate of interplate seismicity is consistent with a pervasively locked megathrust north of 46°N, as indicated by land-based geodetic observations (Burgette et al, 2009;McCaffrey et al, 2013;Schmalzle et al, 2014).…”

Section: Discussionmentioning

confidence: 66%

“…The earthquakes detected near these clusters in our catalog are distributed over a depth range of 10 km in both the upper plate and lower plate. With less subducted sediments (≤400 m thick) (Booth-Rea et al, 2008;Han et al, 2017;MacKay, 1995) and extensive subduction bending deformation in the oceanic crust, the plate interface in this region may be rougher in comparison to the 43°N-45°N region and has conditions favorable for the generation of small earthquakes. Between Figure 6.…”

Section: Discussionmentioning

confidence: 99%

Catalog of Offshore Seismicity in Cascadia: Insights Into the Regional Distribution of Microseismicity and its Relation to Subduction Processes

et al. 2018

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We present a catalog of offshore seismicity generated from Cascadia Initiative (CI) ocean‐bottom seismometer data. Earthquakes were detected within the CI data using a short‐time‐average/long‐time‐average trigger and located using 1‐D velocity models developed from seismic reflection/refraction surveys. The catalog, which contains 271 earthquakes with magnitude 0.4–4.0 along the coasts of Vancouver Island, Washington, Oregon, and Northern California, spans all 4 years of the ocean bottom seismometer deployment and shows distinct along‐strike variations in seismicity consistent with structural observations from recent active source seismic reflection/refraction studies. Seismicity is sparse off Vancouver Island and Washington (49°N–46°N) but increases off northern and central Oregon, corresponding to a roughened, more deformed subducting slab. Widespread earthquakes are observed at near‐interface depths between 46°N and 45°N, though an increase in underthrust sediment thickness between 45°N and 43°N likely restricts seismicity to scattered asperities on the plate interface. South of 43°N, where both the overriding and subducting plates are severely deformed approaching the Mendocino triple junction, seismicity is abundant. We locate an additional 440 events in the Juan de Fuca plate seaward of the deformation front. The higher seismicity south of 46°N is consistent with more extensive intraplate deformation. Along with the complex stress field induced by the Mendocino triple junction, our observations imply that the smoothness and degree of hydration of the incoming plate, which are linked to the amount of underthrust sediment and extent of intraplate deformation, are major contributing factors to the distribution of microseismicity in the Cascadia subduction zone.

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Along‐Trench Structural Variations of the Subducting Juan de Fuca Plate From Multichannel Seismic Reflection Imaging

et al. 2018

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To characterize the along‐strike structural variations of the Juan de Fuca (JdF) Plate as it enters the Cascadia subduction zone, we present prestack time migrated multichannel seismic reflection images of the JdF Plate along a 400‐km‐long trench‐parallel transect extending from 44.3°N to 47.8°N. Beneath the 1.8–3.0‐km‐thick sediment cover, our data reveal basement topographic anomalies associated with a 1.2‐km‐high seamount and in the vicinity of propagator wakes (390–540‐m relief). Weak Moho reflections are imaged beneath the propagator wakes and coincide with reduced Vp in the lower crust and/or uppermost mantle. The inferred locations of propagator wakes in the downgoing plate collocate with some of the boundaries of episodic tremor and slip events. We propose that the structural and hydration heterogeneities associated with these features could lead to anomalous plate interface properties and contribute to episodic tremor and slip segmentation. Intracrustal reflections with apparent dips (20°–30°) consistent with subduction bending normal faults change near 45.8°N, from northward dipping reflections confined to the middle crust in the north to antithetic reflections through the crust in the south, coinciding with a Vp reduction in the lower crust. These observations indicate more extensive faulting deformation and associated hydration of the JdF Plate south of 45.8°N, which likely results from variations of slab dip and resistance to subduction across 46°N. Basement offsets and abrupt depth/amplitude changes in Moho reflections are imaged beneath the four major WNW trending strike‐slip faults that cross the Cascadia deformation front, providing strong evidence of a lower plate origin for these faults.

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Links between sediment consolidation and Cascadia megathrust slip behaviour

Cited by 67 publications

References 56 publications

Coupled Evolution of Deformation, Pore Fluid Pressure, and Fluid Flow in Shallow Subduction Forearcs

Coupled Evolution of Deformation, Pore Fluid Pressure, and Fluid Flow in Shallow Subduction Forearcs

Catalog of Offshore Seismicity in Cascadia: Insights Into the Regional Distribution of Microseismicity and its Relation to Subduction Processes

Along‐Trench Structural Variations of the Subducting Juan de Fuca Plate From Multichannel Seismic Reflection Imaging

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