Determination of the absolute depths of the mantle transition zone discontinuities beneath China: Effect of stagnant slabs on transition zone discontinuities

Abstract

Broadband seismic waveform data are stacked to investigate the mantle discontinuities beneath a station. A polarized filter is devised to remove pseudo-signals in the stacked traces, which might be otherwise misinterpreted as a discontinuity. The depth of a mantle discontinuity determined in previous studies depends on the reference model. We suggest the use of data sets which have a range of epicentral distances to the investigated station. The observed travel time of the P-to-S converted phases as a function of epicentral distance can be used to constrain the proper reference model. When the technique is applied to real data, we can determine the absolute depth of a discontinuity with an accuracy of approximately ±10 km. The method is applied to the broadband data of the CDSN stations. There is no significant depression observed for any of the stations except BJI, implying that the lateral scale of the trough in the '660-km' discontinuity under northeast China is smaller than suggested in previous SS precursors studies. Beneath station BJI, the '410-km' and '660-km' discontinuities are elevated 10 km and depressed 30 km, respectively, resulting in an extremely thick transition zone. This may be attributed to the cold pacific plate that exists in the transition zone of the same region. Meanwhile, at station MDJ, where the subducted pacific plate is also found in the mantle transition zone, a multiple-discontinuity structure is observed rather than a depressed '660-km' discontinuity. At station SSE, there is no depression of the '660-km' discontinuity, suggesting that there is no significant difference of temperature at depths around 660 km between SSE and the average mantle.

Mapping the upper mantle discontinuities beneath China with teleseismic receiver functions

“…This result is consistent with previous results of receiver function analyses (Niu and Kawakatsu, 1998;Li and Yuan, 2003) and correlates well with the hypothesis of a stagnant Pacific slab and Philippine Sea slab suggested by tomography (Fukao et al, 2001;Zhao and Lei, 2004;Huang and Zhao, 2006). The depths of '660' beneath TNC and KSH exceed 680 km, but these depressions are very local, and more dense data are needed to verify the results.…”

“…In the other regions, the variation in the thickness of the transition zone may only reflect local features because of the sparse station coverage; consequently, this topic is beyond the scope of our study. Niu and Kawakatsu (1998) analyzed broadband seismic waveforms of 11 stations belonging to CDSN with a polarized filter to determine the absolute depths of the mantle transition zone discontinuities beneath China. Our results are basically consistent with theirs, with the exception of those for station BJI, and the P410s and P660s of our ORF are very clear (Fig.…”

“…on the depth of the mantle discontinuities beneath China (Niu and Kawakatsu, 1998;Yang and Zhou, 2001), on the lithospheric and upper mantle structure of southern Tibet (Yuan et al, 1997), and on a complex structure of the upper mantle discontinuities beneath northeastern China (Niu and Kawakatsu, 1996;Lebedev et al, 2002;Ai et al, 2003). Although important results have been obtained from such studies, resolution of the topography of upper mantle discontinuities can be improved by making use recent observation data.…”

Receiver function study of the crustal structure of Northeast China: Seismic evidence for a mantle upwelling beneath the eastern flank of the Songliao Basin and the Changbaishan region

“…In this case, significant P wave energy can be seen in receiver functions, which may interfere with the P-to-S converted phase at the Moho and hence affect the measurements. We thus further rotated the vertical and radial components to the P-and SV-components to avoid the interference and to enhance conversion energy (Niu and Kawakatsu, 1998). We employed the "water-level" deconvolution technique (Clayton and Wiggins, 1976) to generate receiver functions:…”

Imaging the mantle transition zone beneath eastern and central China with CEArray receiver functions

“…We further projected the two components to the principal directions (longitudinal and in-plane transverse) computed from the covariance matrix. The receiver functions were then computed from the data projected into this coordinate system (hereafter referred as to P-and SVcomponent) (Vinnik, 1977;Niu and Kawakatsu, 1998;Niu et al, 2005).…”