Evidence for a metastable olivine wedge inside the subducted Mariana slab
Evidence for a metastable olivine wedge inside the subducted Mariana slab
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DOI：
10.1016/j.epsl.2007.03.035
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发表时间：
2007-06
影响因子：
5.3
通讯作者：
S. Kaneshima;T. Okamoto;H. Takenaka
中科院分区：
文献类型：
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作者：
S. Kaneshima;T. Okamoto;H. Takenaka
在马里亚纳州北部俯冲太平洋板块最深震源附近发现了一种异常的地震速度结构。我们观察到一小群深部地震的P波尾波的异常后期，以及属于该群的几对地震之间的异常差分P波慢度。我们用一个5%的低速楔子来解释这些观测结果，这个楔子在590公里的深度有近25公里宽，在630公里处被截断。楔体被两个陡峭的(60°-70°)过渡层所包围，厚度约4公里。板块内部高度局部化的地震异常代表了镶嵌在干燥环木岩(α)中的亚稳橄榄石(γ)的楔形。深地震只发生在亚稳定楔形体的一个边界上，其中一些发生在楔形体之外。根据地震活动相对楔形的空间图像，讨论了深部地震的发生机制。
An anomalous seismic velocity structure is revealed inside the subducted Pacific plate at northern Mariana near the deepest earthquake foci. We observe anomalous later phases in the P wave coda for a small cluster of deep earthquakes and an anomalous differential P wave slowness between a few pairs of the earthquakes belonging to the cluster. We interpret these observations with a 5% low velocity wedge which is nearly 25 km wide at the depth of 590 km and is truncated at 630 km. The wedge is bounded by two steeply dipping (60°–70°) transition layers with the thickness of about 4 km. The highly localized seismic anomaly inside the slab represents a wedge of metastable olivine (α) embedded in dry ringwoodite (γ). Deep earthquakes occur across only one of the boundaries of the metastable wedge, with some of them outside the wedge. The mechanism of deep earthquakes is discussed based on the spatial pattern of seismicity relative to the wedge.