Location of the southern edge of the Gorda slab and evidence for an adjacent asthenospheric window: Results from seismic profiling and gravity

Beaudoin, B. C.; Hole, J. A.; Klemperer, S. L.; Tréhu, Anne M.

doi:10.1029/98jb02231

Cited by 37 publications

(54 citation statements)

References 41 publications

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“…In southern Alaska, there is seismic reflection and refraction evidence that the continental crust has indeed grown by the tectonic emplacement of oceanic crust (Fisher et al, 1989;Fuis et al, 1991;Brocher et al, 1994a). Our view of the models presented by Beaudoin et al (1998) for a seismic line across the landward projection of the Mendo cino Iracture zone is that the Gorda slab is being tectonically emplaced onto the base of North America.…”

Section: Discussionmentioning

confidence: 91%

Synthesis of Crustal Seismic Structure and Implications for the Concept of a Slab Gap beneath Coastal California

Brocher

Brink

Abramovitz

1999

International Geology Review

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Compilation of seismic transects across the central and northern California Coast Ranges provides evidence for the widespread tectonic emplacement beneath the margin of a slab of partially sub ducted oceanic lithosphere. The oceanic crust of this lithosphere can be traced landward from the former convergent margin (fossil trench), beneath the Coast Ranges, to at least as far east as the Coast Range/Great Valley boundary. Comparison of measured shear and compressional wave velocities in the middle crust beneath the Hayward fault with laboratory measurements suggests that the middle crust is a diabase (oceanic crust). Both of these observations are consistent with recent models of the high heat flow and age progression of Neogene volcanism along the Coast Ranges based on tectonic emplacement (stalling) of young, hot oceanic lithosphere beneath the margin, but appear to contra dict the major predictions of the slab-gap or asthenospheric-window model. Finally, the Neogene volcanism and major strike-slip faults in the Coast Ranges occur within the thickest regions (>14 km thick) of the forearc, suggesting that the locations of Cenozoic volcanism and faulting along the margin are structurally controlled by the forearc thickness rather than being determined by the location of a broad slab gap.

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Section: Discussionmentioning

confidence: 91%

Synthesis of Crustal Seismic Structure and Implications for the Concept of a Slab Gap beneath Coastal California

Brocher

Brink

Abramovitz

1999

International Geology Review

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“…A smoothed topographic/bathymetric surface (Figures 1 and 4) defines the top of the model, which is built in three layers. The base of the upper crustal layer is defined by seismic measurements that report a change in seismic velocity associated with silicic rocks into more mafic lower crust ( V p > 6.5 km s −1 ) (Figure 2), and a second layer is defined to lie between the upper crust and the Moho ( V p > 7.9 km s −1 ) (Figure 3) [ Prodehl , 1979; Walter and Mooney , 1982; Colburn and Mooney , 1986; Holbrook and Mooney , 1987; Howie et al , 1993; Page and Brocher , 1993; Catchings and Kohler , 1996; Fliedner and Ruppert , 1996; Holbrook et al , 1996; Parsons and McCarthy , 1996; Godfrey et al , 1997; Hauksson and Haase , 1997; Henstock et al , 1997; Beaudoin et al , 1998; Leitner et al , 1998; Hauksson , 2000; ten Brink et al , 2000; Fuis et al , 2001]. The third layer represents the upper mantle and persists to a depth of 100 km, which encompasses the ∼5‐ to 55‐km thickness of the mantle lithosphere [e.g., Melbourne and Helmberger , 2001].…”

Section: Model Features and Strategymentioning

confidence: 99%

Tectonic stressing in California modeled from GPS observations

Parsons

2006

J. Geophys. Res.

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[1] What happens in the crust as a result of geodetically observed secular motions? In this paper we find out by distorting a finite element model of California using GPS-derived displacements. A complex model was constructed using spatially varying crustal thickness, geothermal gradient, topography, and creeping faults. GPS velocity observations were interpolated and extrapolated across the model and boundary condition areas, and the model was loaded according to 5-year displacements. Results map highest differential stressing rates in a 200-km-wide band along the Pacific-North American plate boundary, coinciding with regions of greatest seismic energy release. Away from the plate boundary, GPS-derived crustal strain reduces modeled differential stress in some places, suggesting that some crustal motions are related to topographic collapse. Calculated stressing rates can be resolved onto fault planes: useful for addressing fault interactions and necessary for calculating earthquake advances or delays. As an example, I examine seismic quiescence on the Garlock fault despite a calculated minimum 0.1-0.4 MPa static stress increase from the 1857 M$7.8 Fort Tejon earthquake. Results from finite element modeling show very low to negative secular Coulomb stress growth on the Garlock fault, suggesting that the stress state may have been too low for large earthquake triggering. Thus the Garlock fault may only be stressed by San Andreas fault slip, a loading pattern that could explain its erratic rupture history.

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“…On‐land seismic reflection and refraction data collected in 1993 and 1994 were used to determine crustal structure in both the subduction (north of MTJ) and transform (south of MTJ) regimes (Trehu et al . 1995; Beaudoin et al 1996; Beaudoin et al 1998; Levander et al . 1998).…”

Section: Previous Studies—the Mendocino Triple Junction Seismic Expmentioning

confidence: 99%

“…While the initial slab window models (e.g. Lachenbruch & Sass 1980; Zandt & Furlong 1982) assumed a crustal thickness of 20–30 km, observations from recent seismic studies suggest a more pronounced crustal thickness variation in the Coast Ranges, with a systematic change from ∼15 km near the coast and north of the triple junction to a maximum thickness of ∼40 km adjacent to the slab edge 200 km further southeast, before thinning again to ∼20 km over the subsequent 150 km south of the triple junction (Verdonck & Zandt 1994; Beaudoin et al 1996; Beaudoin et al 1998; Furlong & Schwartz 2004). These studies imply rapid crustal thinning (a factor of 2 decrease in thickness) over a very short distance (150 km laterally), which should be resolvable as variations in structure on the Moho throughout the Coast Ranges.…”

Section: Introductionmentioning

confidence: 99%

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Abrupt changes in crustal structure beneath the Coast Ranges of northern California - developing new techniques in receiver function analysis

Hayes¹,

Furlong²

2007

Geophysical Journal International

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S U M M A R YNew approaches to receiver function analyses at a suite of broad-band stations in the Coast Ranges of northern California identify rapid changes in crustal thickness accompanied by melt accumulation in the lower crust. These processes are associated with the northward migration of the Mendocino triple junction through the area over the past ∼8 Myr. By simultaneously solving for crustal thickness, Poisson's ratio and Moho strike and dip, we facilitate the application of receiver function analyses in areas of crustal complexity where data sets are sparse. We also introduce a straightforward approach to calculating the Vp/Vs velocity ratio of the seismogenic zone, which is used here to aid in the interpretation of results from the receiver function analysis. Results are consistent with triple junction related crustal modifications occurring in the plate motion direction in a narrow swath of crust between the Máacama and Bartlett Springs Faults. Crustal thicknesses decrease from over 35 km thick in Round Valley, south of the current triple junction location, to 20 km thick just 100 km further south, near Clear Lake. Major crustal thinning is localized to a narrow area of the crust around Redwood Valley, where the Moho dips approximately 17 • to the northeast. This thinning may also be restricted to the lower crust rather than being evenly distributed throughout the crustal column. Coincident with these changes, melts are inferred in the lower crust from low velocity zones and elevated values of Poisson's ratio (σ ≥ 0.32) at two seismic stations. These melts occur in the same area as melt bodies suggested in other seismological studies. Together these results provide the first detailed description of the crustal modifications-and the spatial extent of that deformation-associated with the passage of the Mendocino triple junction.

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Location of the southern edge of the Gorda slab and evidence for an adjacent asthenospheric window: Results from seismic profiling and gravity

Cited by 37 publications

References 41 publications

Synthesis of Crustal Seismic Structure and Implications for the Concept of a Slab Gap beneath Coastal California

Synthesis of Crustal Seismic Structure and Implications for the Concept of a Slab Gap beneath Coastal California

Tectonic stressing in California modeled from GPS observations

Abrupt changes in crustal structure beneath the Coast Ranges of northern California - developing new techniques in receiver function analysis

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