scholarly journals Deep Coseismic Slip in the Cascadia Megathrust can be Consistent with Coastal Subsidence

2021 ◽  
Author(s):  
Diego Melgar ◽  
Valerie Sahakian ◽  
Amanda Thomas
Keyword(s):  
Subduction Zone ◽  
Subduction Zones ◽  
Cascadia Subduction Zone ◽  
Large Magnitude ◽  
Coseismic Slip

At subduction zones, the down-dip limit of slip represents how deep an earthquake can rupture. For hazards it is important - it controls the intensity of shaking and the pattern of coseismic uplift and subsidence. In the Cascadia Subduction Zone, because no large magnitude events have been observed in instrumental times, the limit is inferred from geological estimates of coastal subsidence during previous earthquakes; it is typically assumed to coincide approximately with the coastline. This is at odds with geodetic coupling models, it leaves residual slip deficits unaccommodated on a large swath of the megathrust. Here we will show that ruptures can penetrate deeper into the megathrust and still produce coastal subsidence provided slip decreases with depth. We will discuss the impacts of this on expected shaking intensities

Subduction zone heterogeneity observed across the magnitude spectrum for megathrust earthquakes

2021 ◽  
Author(s):  
Susan Bilek ◽  
Emily Morton
Keyword(s):  
Spatial Heterogeneity ◽  
Subduction Zone ◽  
Stress Drop ◽  
Subduction Zones ◽  
Cascadia Subduction Zone ◽  
Ocean Bottom ◽  
Small Earthquake ◽  
Megathrust Earthquakes ◽  
Seismic Slip ◽  
Subduction Zone Earthquakes

<p>Observations from recent great subduction zone earthquakes highlight the influence of spatial geologic heterogeneity on overall rupture characteristics, such as areas of high co-seismic slip, and resulting tsunami generation.  Defining the relevant spatial heterogeneity is thus important to understanding potential hazards associated with the megathrust. The more frequent, smaller magnitude earthquakes that commonly occur in subduction zones are often used to help delineate the spatial heterogeneity.  Here we provide an overview of several subduction zones, including Costa Rica, Mexico, and Cascadia, highlighting connections between the small earthquake source characteristics and rupture behavior of larger earthquakes.  Estimates of small earthquake locations and stress drop are presented in each location, utilizing data from coastal and/or ocean bottom seismic stations.  These seismicity characteristics are then compared with other geologic and geophysical parameters, such as upper and lower plate characteristics, geodetic locking, and asperity locations from past large earthquakes.  For example, in the Cascadia subduction zone, we find clusters of small earthquakes located in regions of previous seamount subduction, with variations in earthquake stress drop reflecting potentially disrupted upper plate material deformed as a seamount passed.  Other variations in earthquake location and stress drop can be correlated with observed geodetic locking variations. </p>

scholarly journals Relationship between the high-amplitude magnetic anomalies and serpentinized  fore-arc mantle in the Cascadia subduction zone

2021 ◽  
Author(s):  
Wen-Bin Doo
Keyword(s):  
Subduction Zone ◽  
Subduction Zones ◽  
Density Ratio ◽  
Magnetic Anomalies ◽  
High Amplitude ◽  
Cascadia Subduction Zone ◽  
Low Velocity ◽  
Temperature Isotherm ◽  
Magnetization Density ◽  
Cascadia Margin

Abstract A zone of significant high-amplitude magnetic anomalies is observed without a comparable gravity high along the Cascadia margin and is spatially correlated with the low-velocity fore-arc mantle wedge, which is understood to be serpentinized fore-arc mantle and is further considered to be the main source of the high-amplitude magnetic anomalies. To test this hypothesis, the magnetization-density ratio (MDR) is estimated along the Cascadia margin to highlight the physical characteristics of serpentinization (reduced density and increased magnetization). Interestingly, high MDR values are found only in central Oregon, where slab dehydration and fore-arc mantle serpentinization (50%-60% serpentinization) are inferred in conjunction with sparse seismicity. This result may indicate either poorly serpentinized fore-arc mantle (low degree of serpentinization) or that the fore-arc mantle is deeper than the Curie temperature isotherm for magnetite in northern and southern Cascadia. I thus propose that serpentinized fore-arc mantle may not be the major contributor to the high-amplitude magnetic anomalies in these segments. This finding means that magnetic anomaly highs and serpentinized fore-arc mantle may not be completely positively related in subduction zones. On the other hand, the MDR pattern reveals the segmentation of the Cascadia subduction zone, which is consistent with several previous observations.

Effect of plate motion on plume-induced subduction initiation

2021 ◽  
Author(s):  
Marzieh Baes ◽  
Stephan Sobolev ◽  
Taras Gerya ◽  
Robert Stern ◽  
Sascha Brune
Keyword(s):  
Subduction Zone ◽  
Late Cretaceous ◽  
Subduction Zones ◽  
Plate Tectonics ◽  
Plate Motion ◽  
Cascadia Subduction Zone ◽  
Caribbean Plate ◽  
Subduction Initiation ◽  
Southern Margin ◽  
The Caribbean

<p>Subduction zones are key components of plate tectonics and plate tectonics could not begin until the first subduction zone formed. Plume-induced subduction initiation, which has been proposed as triggering the beginning of plate tectonics (Gerya et al., 2015), is one of the few scenarios that can break the lithosphere and recycle a stagnant lid without requiring any pre-existing weak zones. So far, two natural examples of plume-induced subduction initiation have been recognized. The first was found in southern and western margins of the Caribbean Plate (Whattam and Stern 2014). Initiation of the Cascadia subduction zone in Eocene times has been proposed to be the second example of plume-induced subduction initiation (Stern and Dumitru, 2019).</p><p>The focus of previous studies was to inspect plume-lithosphere interaction either for the case of stationary lithosphere (e.g., Gerya et al., 2015) or for moving lithosphere without considering the effect of lithospheric magmatic weakening above the plume head (e.g., Moore et al., 1998). In present study we investigate the response of moving oceanic lithosphere to the arrival of a rising mantle plume head including the effect of magmatic lithospheric weakening. We used 3D numerical thermo-mechanical modeling. Using I3ELVIS code, which is based on finite difference staggered grid and marker-in-cell with an efficient OpenMP multigrid solver (Gerya, 2010), we show that plate motion may affect the plume-induced subduction initiation only if a moderate size plume head (with a radius of 140 km in our experiments) impinges on a young but subductable lithosphere (with the age of 20 Myr). Outcomes indicate that lithospheric strength and plume buoyancy are key parameters in penetration of the plume and subduction initiation and that plate speed has a minor effect. We propose that eastward motion of the Farallon plate in Late Cretaceous time could play a key role in forming new subduction zones along the western and southern margin of the Caribbean plate.</p><p> </p><p>References:</p><p>Gerya, T., 2010, Introduction to Numerical Geodynamic Modelling.. Cambridge University Press.</p><p>Gerya, T.V., Stern, R.J., Baes, M., Sobolev, S.V. and Whattam, S.A., 2015. Plume-induced subduction initiation triggered Plate Tectonics on Earth. Nature, 527, 221–225.</p><p>Moore, W. B., Schubert, G. and Tackley, P., 1998, Three-dimensional simulations of plume-lithosphere interaction at the Hawaiian swell. Science, 279, 1008-1011.</p><p>Stern, R.J., and Dumitru, T.A., 2019, Eocene initiation of the Cascadia subduction zone: A second example of plume-induced subduction initiation? Geosphere, v. 15, 659-681.</p><p>Whattam, S.A. and Stern, R.J., 2014. Late Cretaceous plume-induced subduction initiation along the southern margin of the Caribbean and NW South America: The first documented example with implications for the onset of plate tectonics. Gondwana Research, 27, doi: 10.1016/j.gr.2014.07.011.</p>

An assessment of the megathrust earthquake potential of the Cascadia subduction zone

1988 ◽  
Vol 25 (6) ◽  
pp. 844-852 ◽  
Author(s):  
Garry C. Rogers
Keyword(s):  
United States ◽  
Subduction Zone ◽  
Subduction Zones ◽  
Oceanic Lithosphere ◽  
The United States ◽  
Cascadia Subduction Zone ◽  
The South ◽  
The North ◽  
The Pacific ◽  
Juan De Fuca

The active tectonic setting of the southwest coast of Canada and the Pacific northwest coast of the United states is dominated by the Cascadia subduction zone. The zone can be divided into four segments where oceanic lithosphere is converging independently with the North American plate: the Winona and the Explorer segments in the north, the larger Juan de Fuca segment that extends into both Canada and the United States, and the Gorda segment in the south. The oceanic lithosphere entering the Cascadia subduction zone in all segments is extremely young, less than 10 Ma. Of the other six zones around the Pacific where young (< 20 Ma) lithosphere is being subducted, five have had major thrust earthquakes (megathrust events) on the subduction interface in historic time. An estimation based on potential area of rupture gives maximum possible earthquake magnitudes along the Cascadia subducting margin of 8.2 for the Winona segment, 8.5 for the Explorer segment, 9.1 for the Juan de Fuca segment, and 8.3 for the South Gorda segment. Repeat times for maximum earthquakes, based on the ratios of seismic slip to total slip observed in other subduction zones, are predicted to be up to several hundred years for each segment, well beyond recorded history of the west coast, which began about 1800. Thus the lack of historical seismicity information provides a few constraints on the assessment of the seismic potential of the subduction zone.

Imaging the next Cascadia earthquake: Optimal design for a seafloor GNSS-A network

2021 ◽  
Author(s):  
Eileen L Evans ◽  
Sarah E Minson ◽  
C David Chadwell
Keyword(s):  
Subduction Zone ◽  
Pacific Northwest ◽  
Subduction Zones ◽  
The United States ◽  
Global Navigation Satellite Systems ◽  
Cascadia Subduction Zone ◽  
Satellite Systems ◽  
Concept Of Information ◽  
Outstanding Question ◽  
Global Navigation Satellite

Summary The Cascadia subduction zone in the Pacific Northwest of the United States of America is capable of producing magnitude ∼9 earthquakes, likely often accompanied by tsunamis. An outstanding question in this region, as in most subduction zones, is the degree and spatial extent of strain accumulation, which will eventually release as an earthquake, on the subduction megathrust. Geodetic observations, including those from Global Navigation Satellite Systems (GNSS), may be used to image the strain actively accumulating on a fault before an earthquake ultimately occurs. Technology combining GNSS and underwater acoustic ranging (GNSS-A) is now capable of making centimeter-level horizontal geodetic observations on the seafloor. GNSS-A enables previously inaccessible observations to better image seismogenic portions of the Cascadia subduction zone. Because seafloor geodetic instruments, and the time and logistics associated with observations, can be cost-prohibitive, it is important to identify where deploying seafloor geodetic instruments will provide information that cannot be obtained through a similar investment in onshore geodetic networks. Here we leverage the concept of information entropy to 1) quantify the relative information provided by expanding GNSS observation networks offshore Oregon and Washington and 2) identify optimal locations for a network of seafloor geodetic instruments. The information gained by new observations, and their optimal locations, depends on the expected uncertainties on the seafloor velocity observations, modeling assumptions, and the modeling objectives.

scholarly journals Seismic evidence for megathrust fault-valve behavior during episodic tremor and slip

2020 ◽  
Vol 6 (4) ◽  
pp. eaay5174 ◽  
Author(s):  
Jeremy M. Gosselin ◽  
Pascal Audet ◽  
Clément Estève ◽  
Morgan McLellan ◽  
Stephen G. Mosher ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Subduction Zones ◽  
Seismic Velocity ◽  
Fluid Pressure ◽  
Pore Fluid ◽  
Cascadia Subduction Zone ◽  
Low Velocity ◽  
Seismic Scattering ◽  
Fault Valve ◽  
Episodic Tremor

Fault slip behavior during episodic tremor and slow slip (ETS) events, which occur at the deep extension of subduction zone megathrust faults, is believed to be related to cyclic fluid processes that necessitate fluctuations in pore-fluid pressures. In most subduction zones, a layer of anomalously low seismic wave velocities [low-velocity layer (LVL)] is observed in the vicinity of ETS and suggests high pore-fluid pressures that weaken the megathrust. Using repeated seismic scattering observations in the Cascadia subduction zone, we observe a change in the seismic velocity associated with the LVL after ETS events, which we interpret as a response to fluctuations in pore-fluid pressure. These results provide direct evidence of megathrust fault-valve processes during ETS.

scholarly journals New constraints on coseismic slip during southern Cascadia subduction zone earthquakes over the past 4600 years implied by tsunami deposits and marine turbidites

2017 ◽  
Vol 88 (1) ◽  
pp. 285-313 ◽  
Author(s):  
George R. Priest ◽  
Robert C. Witter ◽  
Yinglong J. Zhang ◽  
Chris Goldfinger ◽  
Kelin Wang ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Cascadia Subduction Zone ◽  
Tsunami Deposits ◽  
Coseismic Slip ◽  
The Past ◽  
Subduction Zone Earthquakes

scholarly journals Cascadia megathrust earthquake rupture model constrained by geodetic fault locking

2021 ◽  
Vol 379 (2196) ◽  
pp. 20200135 ◽  
Author(s):  
Duo Li ◽  
Yajing Liu
Keyword(s):  
Subduction Zone ◽  
Subduction Zones ◽  
Seismogenic Zone ◽  
Cascadia Subduction Zone ◽  
Earthquake Rupture ◽  
Megathrust Earthquake ◽  
Fracture Dynamics ◽  
Coastal Marine ◽  
Rate And State Friction ◽  
Fault Locking

Paleo-earthquakes along the Cascadia subduction zone inferred from offshore sediments and Japan coastal tsunami deposits approximated to M9+ and ruptured the entire margin. However, due to the lack of modern megathrust earthquake records and general quiescence of subduction fault seismicity, the potential megathrust rupture scenario and influence of downdip limit of the seismogenic zone are still obscure. In this study, we present a numerical simulation of Cascadia subduction zone earthquake sequences in the laboratory-derived rate-and-state friction framework to investigate the potential influence of the geodetic fault locking on the megathrust sequences. We consider the rate-state friction stability parameter constrained by geodetic fault locking models derived from decadal GPS records, tidal gauge and levelling-derived uplift rate data along the Cascadia margin. We incorporate historical coseismic subsidence inferred from coastal marine sediments to validate our coseismic rupture scenarios. Earthquake rupture pattern is strongly controlled by the downdip width of the seismogenic, velocity-weakening zone and by the earthquake nucleation zone size. In our model, along-strike heterogeneous characteristic slip distance is required to generate margin-wide ruptures that result in reasonable agreement between the synthetic and observed coastal subsidence for the AD 1700 Cascadia Mw∼9.0 megathrust rupture. Our results suggest the geodetically inferred fault locking model can provide a useful constraint on earthquake rupture scenarios in subduction zones. This article is part of the theme issue ‘Fracture dynamics of solid materials: from particles to the globe’.

Sign in / Sign up

Export Citation Format

Share Document