P-waveform analysis for local subduction geometry south of Puget Sound, Washington

Lapp, David B.; Owens, Thomas; Crosson, Robert S.

doi:10.1007/bf00877168

Cited by 13 publications

(4 citation statements)

References 20 publications

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“…Previous studies in the Vancouver Island region by Cassidy and Ellis [1991,1993] and in the Washington State area by Owens et al [1988] and Lapp et al [1990] have demonstrated this. This method utilizes P waves from distant earthquakes (i.e., teleseismic P-waves) that propagate at near-vertical angles of incidence through the crust beneath the recording site.…”

Section: Receiver Function Analysismentioning

confidence: 63%

The northern limit of the subducted Juan de Fuca Plate system

Cassidy¹,

Ellis²,

Karavas³

et al. 1998

J. Geophys. Res.

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Abstract. Analysis of data recorded at an array of three-component broadband seismograph stations deployed on northern Vancouver Island and the adjacent British Columbia mainland, at the northern end of the Cascadia subduction zone, provides the first constraints on the S wave velocity structure of this region and permits us to define the northern limit of the subducted Juan de Fuca plate system. During a 2-year period, more than 80 teleseisms were recorded at our five stations. The method of receiver function analysis was used to constrain the S velocity structure to upper mantle depths. Beneath the northern three stations, a relatively simple continental crust is interpreted with a well-defined Moho near 37-39 km depth. An upper crustal S velocity discontinuity at these stations is interpreted as the top of the high-velocity rocks of the Wrangellia terrane. In contrast, more complicated structure dominated by pronounced low-velocity zones dipping to the NE are interpreted beneath our southern two stations. The shallower low-velocity zone is 6-8 km thick, has an S velocity contrast of 0.6-1.1 krn/s, and lies within the continental crust. This feature is similar to a pronounced lowvelocity layer (the E zone) imaged beneath southern Vancouver Island. The deeper low-velocity zone is interpreted as the subducted oceanic crust. We interpret the pronounced change in S velocity structure that we observe as the northern limit of the subducted oceanic plate beneath Vancouver Island. This change coincides with significant changes in topography, heat flow, gravity, and geochemistry.

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Section: Receiver Function Analysismentioning

confidence: 63%

The northern limit of the subducted Juan de Fuca Plate system

Cassidy¹,

Ellis²,

Karavas³

et al. 1998

J. Geophys. Res.

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“…Rogers [1983] suggested that this may result in an arching of the subducting plate in this region. In the Puget Sound region of Washington state, both seismicity patterns [Crosson and Owens, 1987;Weaver and Baker, 1988] and the results of receiver function studies [Lapp et al, 1990;Owens et al, 1988] support this hypothesis. Rogers [1988] estimated that the Cascadia subduction zone has the potential to generate megathrust earthquakes in the M~8-9 + range.…”

Section: The Northernmentioning

confidence: 96%

S wave velocity structure of the Northern Cascadia Subduction Zone

Cassidy¹,

Ellis²

1993

J. Geophys. Res.

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Teleseismic receiver functions from an array of portable broadband seismograph stations located in southwestern British Columbia are interpreted to estimate the S wave velocity structure to upper mantle depths across the northern Cascadia subduction zone. At our westernmost station on central Vancouver Island, a prominent low‐velocity zone (ΔVs = −1 km s−1) with a high Poisson's ratio is estimated at 36–41 km depth. This feature correlates with the reflective “E” zone observed in LITHOPROBE reflection data, a region that also exhibits high electrical conductivity and has recently been interpreted as a fluid‐saturated shear zone above the subducting Juan de Fuca (JdF) plate. Analysis of data at our stations to the NE permits this zone to be mapped into the upper mantle, 54 km beneath the British Columbia mainland, and approximately 250 km from the locus of subduction. The subducting oceanic crust is imaged at 47–53 km depth dipping 15°± 5° in the direction N30°E ± 20° beneath central Vancouver Island. The dip angle increases to 22° ± 5° at a depth of 60–65 km beneath the Strait of Georgia. The results of this analysis provide the first definitive evidence for the location of the subducting plate in this region and indicate that the seismicity at depth occurs within the oceanic crust. The dip direction of N30°E at each station provides new evidence that the JdF plate is arched upward as it subducts in this region. A low‐velocity zone that coincides with the “C” reflectors beneath Vancouver Island is interpreted to extend east to the British Columbia mainland near the base of the North American crust. The top of this zone, near 20–26 km depth, lies near the lower limit of shallow seismicity. The continental Moho is estimated to be 36 km below the Strait of Georgia.

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“…[1987], and Owens [1987] and in the Pacific Northwest by Owens and Crosson [1988], Owens et al . [1988] and Lapp et al . [1990].…”

Section: Crustal Seismic Studies Using Various Techniquesmentioning

confidence: 99%