Detection of lower mantle scatterers northeast of the Marianna subduction zone using short-period array data
Detection of lower mantle scatterers northeast of the Marianna subduction zone using short-period array data
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DOI：
10.1029/97jb02565
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发表时间：
1998-03
影响因子：
--
通讯作者：
S. Kaneshima;G. Helffrich
中科院分区：
文献类型：
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作者：
S. Kaneshima;G. Helffrich
加利福尼亚州北部的华盛顿大学和南加州的一系列深部马里亚纳俯冲带地震的短周期地震台阵记录显示，在P之后有近90和105次意外的清晰到达。我们使用阵列技术测量这些震相相对于P的慢度、到达时间和到达方位，以找出它们在地幔中的发射位置。综合不同地震的慢度和方位向后偏差以及震源随深度的移出，我们发现它们最可能的起因是在距∼30 0公里的中下地幔的2 5.7°N 148.2°E 1 590公里和2 5.5°N 151.0°E 1 85 0公里的点散射点上的S-P转换。这些特征表明，在下地幔中部有弹性明显的物质，如果是俯冲板块的碎片，则与当代俯冲无关。它们可能代表了来自深部地幔或D“的上升对流物质，但它们本质上并不是纯粹的热物质。作为化学上不同的物体，它们可能代表了在地球化学上识别的同位素和微量元素组分的潜在储集层。
Short period University of Washington, northern California, and southern California seismic array records of a sequence of deep Mariana subduction zone earthquakes show unexpected clear arrivals nearly 90 and 105 s following P. We measure slowness, arrival time, and arrival azimuth of these phases relative to P using array techniques to find where they emanate in the mantle. By combining slowness and back azimuth deviations and the move-out with depth of the arrivals from different earthquakes, we find their most probable origin is through S-to-P conversion at point scatterers in the mid- to lower mantle at 25.7°N 148.2°E 1590 km and 25.5°N 151.0°E 1850 km respectively, separated by ∼300 km. These features indicate elastically distinct material in the middle of the lower mantle, which, if fragments of subducted slabs, are not related to contemporary subduction. They may represent upwelling convective material from the deep mantle or D″, but they are not purely thermal in nature. As chemically distinct bodies, they may represent potential reservoirs of the isotopic and trace element components recognized geochemically.