Strong seismic scatterers near the core–mantle boundary north of the Pacific Anomaly

Abstract

a b s t r a c tTomographic images have shown that there are clear high-velocity heterogeneities to the north of the Pacific Anomaly near the core-mantle boundary (CMB), but the detailed structure and origin of these heterogeneities are poorly known. In this study, we analyze PKP precursors from earthquakes in the Aleutian Islands and Kamchatka Peninsula recorded by seismic arrays in Antarctica, and find that these heterogeneities extend $400 km above the CMB and are distributed between 30°and 45°N in latitude. The scatterers show the largest P-wave velocity perturbation of 1.0-1.2% in the center (160-180°E) and $0.5% to the west and east (140-160°E, 180-200°E). ScS-S differential travel-time residuals reveal similar features. We suggest that these seismic scatterers are the remnants of ancient subducted slab material. The lateral variations may be caused either by different slabs, or by variations in slab composition resulting from their segregation process.

Ultra-low velocity zone heterogeneities at the core–mantle boundary from diffracted PKKPab waves

“…These strong lateral heterogeneities are much larger than those calculated from global tomographic models and imply significantly complex structures at the CMB that have long been known to exist [see Garnero (2000); Lay and Garnero (2011) for a review], even on the small-scale level (Ma et al 2016;Sun et al 2016). The explanations for these heterogeneities, however, are still inconclusive.…”

“…To resolve this problem, one way is to compare with other phases that sample similar regions, at least in one side, such as PcP, ScP, SPdKS and PKP (e.g., Idehara 2011; Jensen et al 2013;Ma et al 2016). In most cases, this may be difficult to do because of limited earthquake and station distributions.…”

Seismic Evidence for a Paleoslab in the D" Layer Residing Adjacent to the Southeastern Edge of the Perm Anomaly

“…Seismic pairs like S-ScS (e.g., He & Wen, 2011) and SKS-SKKS (e.g., Zhang et al, 2009) that have similar path in the upper mantle are not only useful to characterize the seismic anisotropy (e.g., He & Long, 2011;Long, 2009;Restivo & Helffrich, 2006;Wookey et al, 2005) but also useful to constrain the structural heterogeneity (e.g., Ma et al, 2016;Rao & Kumar, 2014) in the lowermost mantle by analyzing their differential traveltimes. In this paper, we analyzed differential traveltime residuals of SmKS relative to the IASP91 model (Kennett & Engdahl, 1991) sampling the southeastern edge of the Perm Anomaly.…”

“…Some hot spots and large igneous provinces are perhaps originated from the edges of the LLSVPs (e.g., Burke et al, ; Steinberger & Torsvik, ; Thorne et al, ; Torsvik et al, ). Subducted slabs appear to be located adjacent to the edges of the Pacific LLSVP (e.g., Idehara et al, ; Ma et al, ). Seismic anisotropy—a consequence of strain‐induced lattice‐preferred orientation of mineral in the lowermost mantle (e.g., Wentzcovitch et al, ; a detailed description about seismic anisotropy in the D" layer can be referred to a review paper by Romanowicz & Wenk, )—has also been detected in the D" layer adjacent to the edges of the LLSVPs (e.g., Cottaar & Romanowicz, ; Ford et al, ; Lynner & Long, ; Wang & Wen, ), although different mechanisms, such as the shape preferred orientation of elastically distinct materials (Kendall & Silver, ), cannot be fully ruled out; it has been primarily attributed to the dynamic interaction between the LLSVPs and subducted slabs (e.g., Tackley, ; Tan et al, , ).…”

“…Some hot spots and large igneous provinces are perhaps originated from the edges of the LLSVPs (e.g., Burke et al, 2008;Steinberger & Torsvik, 2012;Thorne et al, 2004;Torsvik et al, 2006). Subducted slabs appear to be located adjacent to the edges of the Pacific LLSVP (e.g., Idehara et al, 2013;Ma et al, 2016). Seismic anisotropy-a consequence of strain-induced lattice-preferred orientation of min-…”