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No basalt accumulation and segregation atop the 660-km discontinuity beneath the Sea of Okhotsk

Earth and Planetary Physics 2024年第4期8卷 621-631页

作者： BingXin Zhou XiaoBo He Marine Science and Technology College Zhejiang Ocean UniversityZhoushan Zhejiang 316022China

Recent seismic evidence shows that basalt accumulation is widespread in the mantle transition zone(MTZ),yet its ubiquity or sporadic nature remains *** investigate this phenomenon further,we characterized the velocity structure across the 660-km discontinuity that separates the upper mantle from the lower mantle beneath the Sea of Okhotsk by modeling the waveform of the S660P phase,a downgoing S wave converting into a P wave at the 660-km *** waves were excited by two regional>410-km-deep events and were recorded by stations in central *** findings showed no need to introduce velocity anomalies at the base of the MTZ to explain the S660P waveforms because the IASP91 model adequately reproduced the *** finding indicates that the basalt accumulation has not affected the bottom of the MTZ in the study ***,this discontinuity is primarily controlled by temperature or water content variations,or ***,we argue that the basalt accumulation at the base of the MTZ is sporadic,not ubiquitous,reflecting its heterogeneous distribution.

关键词： 660-km discontinuity S660P basalt segregation mantle transition zone western pacific subduction zone

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Spatial variations of the 660-km discontinuity in the western pacific subduction zones observed from CEArray triplication data

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Earthquake Science 2011年第1期24卷 77-85页

作者： Baoshan Wang Fenglin Niu Institute of Geophysics China Earthquake Administration Beijing 100081 China Department of Earth Science Rice University Houston TX 77005 USA

We examined the spatial variation of velocity structures around the 660-kin discontinuity at the western pacific subduction zones by waveform modeling of triplication data. Data from two deep earthquakes beneath Izu-Bonin and Northeast China are used. Both events were well recorded by a dense broadband seismic network in China （CEArray）. The two events are located at approximately the same distance to the CEArray, yet significant differences are observed in their records：（1） the direct arrivals traveling above the 660-km discontinuity （AB branch） are seen in a different distance extent： -29° for the NE China event, -23° for Izu-Bonin event; （2） the direct （AB） and the refracted waves at the 660-km （CD branch） cross over at 19.5° and 17° for the NE China and the Izu-Bonin event, respectively. The best fitting model for the NE China event has a broad 660-km discontinuity and a constant high velocity layer upon it; while the Izu-Bonin model differs from the standard IASP91 model only with a high velocity layer above the 660-km discontinuity. Variations in velocity models can be roughly explained by subduction geometry.

关键词： P-wave triplication 660-km discontinuity western pacific subduction zone

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