Seismic evidence against a mantle chemical discontinuity near 660 km depth beneath Izu‐Bonin
Seismic evidence against a mantle chemical discontinuity near 660 km depth beneath Izu‐Bonin
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DOI：
10.1029/96gl03829
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发表时间：
1997-02
影响因子：
5.2
通讯作者：
J. C. Castle;K. Creager
中科院分区：
文献类型：
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作者：
J. C. Castle;K. Creager
我们分析了美国西部数百个地震仪台站记录的12次深伊豆-小笠原地震的P波尾波，以寻找近源地幔不连续引起的小振幅相位的证据。对于几乎每一个事件，尾波中的主导相位都是从深度从650到690 km的近水平不连续面进行S-到-P转换的结果。这被解释为热抑制尖晶石到钙钛矿和镁钨铁矿的相变。如果660公里的地震不连续性也与化学变化有关，那么它将被俯冲板片动态地压低。我们一直看到，有没有近水平的不连续性之间的700和1000公里的剪切波速度对比度超过1%，这一观察的地方的假设的化学不连续性分离的上地幔和下地幔的属性的限制。
We analyze P‐wave codas from 12 deep Izu‐Bonin earthquakes recorded by hundreds of Western United States seismograph stations for evidence of small‐amplitude phases caused by near‐source mantle discontinuities. For nearly every event, the dominant phase in the coda is the result of an S‐to‐P conversion from a nearly horizontal discontinuity ranging in depth from 650 to 690 km. This is interpreted as a thermally depressed spinel to perovskite and magnesiowüstite phase transition. If the 660‐km seismic discontinuity is also associated with a change in chemistry, it would be dynamically depressed by a subducting slab. We consistently see that there is no nearly horizontal discontinuity between 700 and 1000 km with shear wave velocity contrast exceeding 1%; this observation places constraints on the properties of a postulated chemical discontinuity separating the upper and lower mantles.