Models of downdip frictional coupling for the Cascadia Megathrust

Stanley, Dal; Villaseñor, Antonio

doi:10.1029/1999gl005441

Cited by 8 publications

(12 citation statements)

References 16 publications

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“…A seismicity cross‐section taken normal to the Cascadia subduction zone (Fig. 12) uses relocations from Stanley & Villasenor (2000) of microseismicity based on observations from the regional Pacific Northwest Seismic Network. The Nisqually earthquake occurred within and near a subtle change in dip of the Wadati–Benioff zone defined by the prior seismicity.…”

Section: Deeper Earthquakes With Average Apparent Stressmentioning

confidence: 99%

“…The hypocentre is also situated just before a downdip gap in seismicity occurs in the Wadati–Benioff zone. The proximity of the East Pacific rise spreading centre and the shallow dip make this subduction zone a warm‐slab environment (Stanley & Villasenor 2000). The τ a for this event was 0.51 MPa, average for this population.…”

Section: Deeper Earthquakes With Average Apparent Stressmentioning

confidence: 99%

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Apparent stress, fault maturity and seismic hazard for normal-fault earthquakes at subduction zones

Choy¹,

Kirby²

2004

Geophysical Journal International

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S U M M A R YThe behavior of apparent stress for normal-fault earthquakes at subduction zones is derived by examining the apparent stress (τ a = µE S /M 0 , where E S is radiated energy and M 0 is seismic moment) of all globally distributed shallow (depth, h < 70 km) earthquakes with normal-fault mechanisms that occurred in or near subduction zones between 1987 and 2001 for which E S and M 0 are available. Accurately determined hypocentres from the Engdahl-HilstBuland (EHB) catalogue establish the fine detail of the Wadati-Benioff zone. In many cases, we can relate trends in apparent stress to specific features within the subduction zone and compare these with trends for interplate-thrust earthquakes in the same subduction zones. There are two depth ranges over which τ a for normal-fault earthquakes shows maxima. The highest and most anomalous values of τ a are found in the deeper depth range from 35 to 70 km. The high-τ a events (up to 5 MPa) are characteristically intraslab and in proximity to zones of intense deformation such as a sharp slab bend or where opposing slabs collide. High-τ a events in the region of the shallower maximum (hypocentres between 10-35 km and τ a > 1 MPa) are also generally intraslab, but occur where the lithosphere has just begun subduction beneath the overriding plate. They usually occur in cold slabs near trenches where the direction of plate motion across the trench is oblique to the trench axis, or where there are local contortions or geometrical complexities of the plate boundary. Lower τ a (<1 MPa) is associated with events occurring at the outer rise (OR) complex (between the OR and the trench axis), as well as with intracrustal events occurring just landward of the trench. The average apparent stress of intraslab-normal-fault earthquakes is considerably higher than the average apparent stress of interplate-thrust-fault earthquakes. In turn, the average τ a of strike-slip earthquakes in intraoceanic environments is considerably higher than that of intraslab-normal-fault earthquakes. The variation of average τ a with focal mechanism and tectonic regime suggests that the level of τ a is related to fault maturity. Lower stress drops are needed to rupture mature faults such as those found at plate interfaces that have been smoothed by large cumulative displacements (from hundreds to thousands of kilometres). In contrast, immature faults, such as those on which intraslab-normal-fault earthquakes generally occur, are found in cold and intact lithosphere in which total fault displacement has been much less (from hundreds of metres to a few kilometres). Also, faults on which high τ a oceanic strike-slip earthquakes occur are predominantly intraplate or at evolving ends of transforms. At subduction zones, earthquakes occurring on immature faults are likely to be more hazardous as they tend to generate higher amounts of radiated energy per unit of moment than earthquakes occurring on mature faults. We have identified earthquake pairs in which an interplate-thrust and an intraslab-normal e...

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Section: Deeper Earthquakes With Average Apparent Stressmentioning

confidence: 99%

Section: Deeper Earthquakes With Average Apparent Stressmentioning

confidence: 99%

Apparent stress, fault maturity and seismic hazard for normal-fault earthquakes at subduction zones

Choy¹,

Kirby²

2004

Geophysical Journal International

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“…In this paper we present combined seismic and gravity analyses around the Strait of Juan de Fuca, a 100‐km long and 20–25 km wide west‐northwest oriented topographic depression, which separates Vancouver Island from the Olympic Peninsula. The analyses are aimed at (1) resolving the velocity structure and thickness of sedimentary basins [ Fisher et al , 1999] and the Eocene oceanic Crescent‐Siletz terrane, which may be thicker than previously recognized and is thought to be composed of strong crustal blocks of oceanic origin that play an important role in crustal deformation [ Tréhu et al , 1994; Stanley and Villaseñor , 2000; Ramachandran , 2001]; (2) constraining the nature of lower crust high‐velocity zones [ Spence et al , 1985; Drew and Clowes , 1990] and a large reflector band called E that has been interpreted to be a present or former decollement [ Yorath et al , 1985; Calvert , 1996; Green et al , 1986; Clowes et al , 1987; Hyndman , 1988; Calvert and Clowes , 1990; Hyndman et al , 1990]; and (3) determining the geometry of the downgoing oceanic crust and mantle [ Calvert , 1996] by comparing our results with local microearthquakes. This study using wide‐angle data will then test previous interpretations of Crescent‐Siletz terrane thickness, of the E reflection and of the geometry of the Moho reflections on the Multichannel Seismic (MCS) data.…”

Section: Introductionmentioning

confidence: 99%

Crustal structure beneath the Strait of Juan de Fuca and southern Vancouver Island from seismic and gravity analyses

et al. 2003

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[1] Wide-angle and vertical incidence seismic data from Seismic Hazards Investigations in Puget Sound (SHIPS), gravity modeling, and seismicity are used to derive twodimensional crustal models beneath the Strait of Juan de Fuca. The Eocene volcanic Crescent-Siletz terrane is significantly thicker than previously recognized and extends from near the surface to depths of 22 km or greater. For the northern strait, a weak midcrustal reflector, dipping east from 12-to 22-km depth, is inferred from wide-angle reflections. A stronger deeper reflector, dipping eastward from 23-to 36-km depth, is associated with the top of ''reflector band E,'' a zone of high reflectivity on coincident Multichannel Seismic (MCS) data, interpreted as a shear zone. A high-velocity zone (7.60 ± 0.2 km s À1 ) between these reflectors is interpreted as a localized slice of mantle accreted with the overlying Crescent-Siletz terrane. For the southern strait, no deep high-velocity layer is observed and the E-band reflectivity is weaker than to the north. A strong deep reflector, interpreted as the oceanic Moho dips eastward from 35 to 42 km. Seismicity within the subducting slab occurs mainly above the inferred oceanic Moho. Gravity modeling, constrained by the wide-angle seismic models and seismicity, is consistent with the inferred large thickness of Crescent-Siletz and high-density rocks (3030 kg m À3 ) in the lower crust.

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“…3) because topography is not included in model V1.6. The surface of the continental crust below MSL was controlled by a smoothed continental shoreline and numerous published active and passive source seismic results along the continental margin (for example, Trehu and others, 1994;Clowes and others, 1997;Flueh and others, 1998;Fuis, 1998;Gulick and others 1998;Fleming and Trehu, 1999;Parsons and others, 1999;Stanley and Villaseñor, 2000;Bostock and others, 2002;and Ramachandran and others, 2006).…”

Section: Continental Crustmentioning

confidence: 99%

“…3 and 5). Parameter V P is derived from results of Parsons and others (1999) and numerous active-source marine seismic surveys (Trehu and others, 1994;Clowes and others, 1997;Flueh and others, 1998;Fuis, 1998;Gulick and others, 1998;Fleming and Trehu, 1999;Parsons and others, 1999;Stanley and Villaseñor, 2000;Bostock and others, 2002). Parameter V P varies primarily as a function of depth.…”

Section: Oceanic Sedimentmentioning

confidence: 99%

P- and S-wave velocity models incorporating the Cascadia subduction zone for 3D earthquake ground motion simulations, Version 1.6—Update for Open-File Report 2007–1348

Stephenson¹,

Reitman²,

Angster³

2017

Open-File Report

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For more information on the USGS-the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment-visit https://www.usgs.gov or call 1-888-ASK-USGS.For an overview of USGS information products, including maps, imagery, and publications, visit https://store.usgs.gov.Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. Suggested citation:Stephenson, W.J., Reitman, N.G., and Angster, S.J., 2017, P-and S-wave velocity models incorporating the Cascadia subduction zone for 3D earthquake ground motion simulations, version 1. AcknowledgmentsThe V P and V S property volumes of model V1.6 were greatly improved by feedback from end-users including Art Frankel (U.S. Geological Survey [USGS]), Andy Delorey (Los Alamos National Laboratory), and John Vidale (University of Washington). We thank Jack Odum and Robert Williams (USGS) for their technical reviews, which greatly improved this manuscript. Special thanks to Jordan Bretthauer (USGS) for assistance in developing figure 1 of this report. Discussions with numerous collaborators and other interested parties seeking components of the model for their research helped prompt us to formally complete this updated documentation. This research was supported by funding from the USGS Earthquake Hazards Program. IntroductionIn support of earthquake hazards studies and ground motion simulations in the Pacific Northwest, threedimensional (3D) P-and S-wave velocity (V P and V S , respectively) models incorporating the Cascadia subduction zone were previously developed for the region encompassed from about 40.2°N. to 50°N. latitude, and from about 122°W. to 129°W. longitude ( fig. 1). This report describes updates to the Cascadia velocity property volumes of model version 1.3 ([V1.3]; Stephenson, 2007), herein called model version 1.6 (V1.6). As in model V1.3, the updated V1.6 model volume includes depths from 0 kilometers (km) (mean sea level) to 60 km, and it is intended to be a reference for researchers who have used, or are planning to use, this model in their earth science investigations. To this end, it is intended that the V P and V S property volumes of model V1.6 will be considered a template for a community velocity model of the Cascadia region as additional results become available. With the recent and ongoing development of the National Crustal Model (NCM; Boyd and Shah, 2016), we envision any future versions of this model will be directly integrated with that effort. BackgroundThe Cascadia subduction zone stretches for over 1,000 km, from the Mendocino Triple Junction off the northern California coast northward to Vancouver Island, Canada ( fig. 2). The primary reasons for developing these model volumes are (1) for simulat...

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Models of downdip frictional coupling for the Cascadia Megathrust

Cited by 8 publications

References 16 publications

Apparent stress, fault maturity and seismic hazard for normal-fault earthquakes at subduction zones

Apparent stress, fault maturity and seismic hazard for normal-fault earthquakes at subduction zones

Crustal structure beneath the Strait of Juan de Fuca and southern Vancouver Island from seismic and gravity analyses

P- and S-wave velocity models incorporating the Cascadia subduction zone for 3D earthquake ground motion simulations, Version 1.6—Update for Open-File Report 2007–1348

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