Modeling the ratios of SKKS and SKS amplitudes with ultra‐low velocity zones at the core‐mantle boundary
Modeling the ratios of SKKS and SKS amplitudes with ultra‐low velocity zones at the core‐mantle boundary
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DOI：
10.1029/2009gl040030
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发表时间：
2009-10
影响因子：
5.2
通讯作者：
Yang Zhang;J. Ritsema;M. Thorne
中科院分区：
文献类型：
--
作者：
Yang Zhang;J. Ritsema;M. Thorne
在105-115°之间，SKS波形由于SPdKS的形成而变得复杂，SPdKS是一种具有沿核幔边界沿着的P衍射段的波。虽然以前的研究主要集中在SPdKS从SKS中移出，但我们分析了SKS振幅的伴随降低。长周期SKKS/SKS振幅比呈现相干的全局模式。SKKS/SKS在北美和南美的汤加-斐济深地震记录中相对较大，但在南美地震的欧洲记录和印度尼西亚地震的北美记录中类似PREM。SKKS/SKS的建模表明，超低速带（ULVZ），即地幔底部厚度约为10-20 km且剪切速度降低20- 30%的层，需要解释高SKKS/SKS比率和SPdKS的早期移出。
Between 105–115° degrees, the SKS waveform is complicated by the formation of SPdKS, a wave that has segments of P diffraction along the core mantle boundary. While previous studies have primarily focused on the move‐out of SPdKS from SKS, we analyze the concomitant reduction of the SKS amplitude. Long‐period SKKS/SKS amplitude ratios present a coherent global pattern. SKKS/SKS is relatively large in North and South American recordings of deep Tonga‐Fiji earthquakes but PREM‐like in European recordings of earthquakes in South America and North American recordings of earthquakes in Indonesia. Modeling of SKKS/SKS indicate that Ultra‐Low Velocity Zones (ULVZs), layers at the base of the mantle with a thickness of about 10–20 km and a shear velocity reduction between 20–30%, are required to explain high SKKS/SKS ratios and the early move‐out of SPdKS.