Ultra-Low velocity zones near the core-mantle boundary from broadband PKP precursors
Ultra-Low velocity zones near the core-mantle boundary from broadband PKP precursors
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DOI：
10.1126/science.279.5357.1701
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发表时间：
1998-03
期刊：
影响因子：
56.9
通讯作者：
L. Wen;D. Helmberger
中科院分区：
文献类型：
--
作者：
L. Wen;D. Helmberger
利用PKP相的短周期和长周期前兆研究了西太平洋核幔边界附近的超低速带。合成地震图是用一种混合方法计算的，这种方法处理地震波通过二维复杂结构的传播。长周期的前兆是由60至80公里高的高斯形ULVZ解释的，在100至300公里的范围内，P速度下降至少7%。短周期的前兆表明，伴随着这些较大的高斯形结构存在较小规模的异常。这些精细的结构可能是由剧烈的小尺度对流或地幔底部热边界层的不稳定性引起的部分熔融区域，或者两者兼而有之。
Short- and long-period precursors of the PKP phase were used to study an ultra-low velocity zone (ULVZ) near the core-mantle boundary beneath the Western Pacific. Synthetic seismograms were computed from a hybrid method, which handles seismic wave propagation through two-dimensional complex structures. Long-period precursors were explained by Gaussian-shaped ULVZs of 60 to 80 kilometers height with P velocity drops of at least 7 percent over 100 to 300 kilometers. Short-period precursors suggest the presence of smaller scale anomalies accompanying these larger Gaussian-shaped structures. These fine structures may be areas of partial melt caused by vigorous small-scale convection or the instability of a thermal boundary layer at the mantle's base, or both.