Abstract
Abstract High-resolution receiver function (RF) images of the upper mantle structure beneath the Japan Islands are obtained by RF analysis of the P-wave coda portions of 389 teleseismic events observed at 138 high-density broadband stations. We construct RFs through frequency-domain division using a water level of 0.01 and Gaussian low-pass filters of 1.0, 0.5, 0.3, and 0.1 Hz, and produce depth-migrated RFs using the one-dimensional IASP91 velocity model. The RF images clearly resolve the subducting Pacific Plate to a depth of 200 km, and reveal a local 30 km elevation of the 410 km discontinuity within the subducting plate. The 660 km discontinuity is also found to exhibit a broad 50 km depression under the influence of the stagnating slab. From analysis of the frequency dependence of the RFs, the thickness of the 410 km discontinuity is inferred to vary on a relatively local scale, whereas the 660 km transition is sharp throughout the Japan Islands.
Highlights
It is widely accepted that seismic velocity discontinuities exist globally at depths of approximately 410 and 660 km in the upper mantle
The interpreted PAC and 410 and 660 km discontinuities are indicated by black lines in the figure, corresponding to positive receiver function (RF) amplitudes
The 410 km discontinuity was found to exhibit a local elevation of 30 km within the cold subducting PAC, while the 660 km discontinuity was revealed to undergo a gradual depression (a) 0
Summary
It is widely accepted that seismic velocity discontinuities exist globally at depths of approximately 410 and 660 km in the upper mantle. These discontinuities exhibit global and local undulations due to both thermal anomalies in the mantle and the Clapeyron slope associated with mineral phase change. Previous seismic reflection and refraction studies have revealed the global variations in the depth and thickness of the upper mantle discontinuities. Recent studies have revealed more details about the depth variations of the upper mantle discontinuities (e.g., Flanagan and Shearer, 1998; Gu and Dziewonski, 1998; Gu et al, 2003). In local-scale surveys focusing on the Japan subduction zone, Castle and Creager (1997) suggested that the 660 km discontinuity is depressed by about
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