Topography of the 410 and 660 km discontinuities beneath the Korean Peninsula and southwestern Japan using teleseismic receiver functions

Abstract

Topography of the 410 and 660 km seismic upper mantle discontinuities beneath the Korean Peninsula and southwestern Japan were determined using teleseismic receiver functions. P receiver functions were migrated from delayed times to corresponding piercing (conversion) points of P-to-S converted phases, using one-dimensional (1-D) and three-dimensional (3-D) models. Receiver functions were then stacked using Common Conversion Point (CCP) techniques, to enhance signal-to-noise ratios and thereby reduce uncertainty (noise). The 410 and 660 km discontinuities were clearly imaged, as positively valued amplitude peaks of CCP stacked receiver functions in the study area. Topographic variations were roughly consistent with the low temperature of the subducting Pacific Plate. However, the complex structure of the subducting Pacific Plate produced distinct changes of upper mantle discontinuities, which cannot be explained by temperature variations alone. Depression of the 410 km discontinuity, observed in a wide region extending from the Korean Peninsula to Kyushu Island, may be related to trench rollback history. Furthermore, the topography of the 660 km discontinuity varies significantly with latitude. At latitudes higher than 38°N, its depth remains unchanged, despite the presence of the stagnant slab, while significant depression has been observed at latitudes below 36°N. This may have been caused by differences in the angles of subduction of the Japan slab and the Izu-Bonin slab. However, heterogeneity of the water content of slabs may also have contributed to this topographical difference.

Topography of the 410 km and 660 km discontinuities beneath the Japan Sea and adjacent regions by analysis of multiple‐ScS waves

“…The largest uplift is located beneath the southwest Japan islands, mostly to the southeast of Shikoku Island. The average local elevation of the 410 in this area has been reported to be ~15–20 km [ Tonegawa et al ., ], with a maximum value of ~20 km [ Lee et al ., ] measured by broadband receiver function analysis, ~10–20 km by short‐period receiver function study [ Niu et al ., ], and ~20 km through long‐period multiple‐ ScS waveform modeling [ Tono et al ., ]. Our results here agree with previous studies in the southwest Japan islands.…”

“…Lee et al . [] investigated the undulation of the 410 beneath the Korean Peninsula and adjacent regions and detected a significantly depressed 410 centered around 37°N, 128°E with a value of ~20 km in both 1‐D and 3‐D velocity corrected models (dashed box A in Figure a). Recent work by Liu et al .…”

“…In our study, we observed a depressed 410 beneath the west Japan Sea and eastern edge of northeast China. However, with the combination of previous studies, the landward extension of the depressed 410 is of large scale with a lateral range of at least 800–1000 km [ Lee et al ., ; Liu et al ., ]. We speculate that the broadly depressed 410 beneath the west Japan Sea, part of Okhotsk Sea, and northeast China might be caused by high water content at the top of the MTZ.…”

“…The topography of the upper mantle discontinuities in the northwest Pacific region has been investigated using a variety of methods. For example, there are studies based on relatively high‐frequency receiver function techniques [ Lebedev et al ., ; Ai et al ., ; Li and Yuan , ; Niu et al ., ; Tonegawa et al ., ; Kawakatsu and Yoshioka , ; Lee et al ., ], source‐sided SdP‐converted waves [ Tibi and Wiens , ; Li et al ., ], long‐period SS precursors [ Flanagan and Shearer , ; Gu and Dziewonski , ; Gu et al ., ], and multiple‐ ScS reverberations [ Revenaugh and Jordan , ; Revenaugh and Sipkin , , ; Tono et al ., ]. Short‐period seismic studies, such as receiver function studies, have high lateral resolution and frequently are applied to study local or regional structure.…”

Large‐scale mantle discontinuity topography beneath Europe: Signature of akimotoite in subducting slabs

“…Previous studies have interpreted observations of depressed 660 in terms of increased water content in regions where subducted slabs are seen by increased shear wave velocities within the transition zone. Such strong depressions on the 660 in regions with subducting slabs have been seen beneath the Philippines [ Suetsugu et al , ], the western United States [ Cao and Levander , ], the Red Sea [ Mohamed et al , ], and Korea [ Lee et al , ]. Experiments on ringwoodite and pyrolite samples hydrated with 2 wt % water show an increased pressure of the dissociation of ringwoodite and a steeper Clapeyron slope [ Litasov et al , ; Ghosh et al , , Figure a].…”