Shear-wave polarization anisotropy and subduction-induced flow in the mantle wedge of northeastern Japan
Shear-wave polarization anisotropy and subduction-induced flow in the mantle wedge of northeastern Japan
复制标题
DOI：
10.1016/j.epsl.2004.06.011
复制
发表时间：
2004-09-15
影响因子：
5.3
通讯作者：
Hasegawa, A
中科院分区：
文献类型：
--
作者：
Nakajima, J;Hasegawa, A
研究了日本东北部中部地区的剪切波偏振各向异性。分析了77个台站记录的293个中深源地震的S震相，得到了1286个分裂参数。所得到的结果表明，在整个电弧分裂参数的系统变化。在研究区西侧的台站获得的超前剪切波偏振方向（快方向）接近东西向，与太平洋板块和北美/鄂霍次克板块之间的相对板块运动方向近平行。相反，在研究区域东侧的站点获得的快速方向近似为N-S方向。西侧的车站比东侧的车站有更大的平均延迟时间。这些变化表明，各向异性的性质是相当不同的东西两侧。橄榄石变形的实验研究和板块驱动流动的数值模拟预测，橄榄石的晶格择优取向导致的快速方向近平行于日本东北部地幔楔的条件下的流动方向。因此，我们推断，由流动引起的应变所产生的橄榄石的晶格优选取向是最有可能的候选各向异性，产生分裂与E-W快方向。在东侧的各向异性的三个可能的原因被认为是：在地幔楔中的富水橄榄石的变形，沟平行流动的地幔楔由于沿走向倾角的变化在板和各向异性的地壳和板。然而，我们无法确定哪些原因是主要原因。东侧各向异性的成因有待进一步系统研究。(C)2004 Elsevier B. V.保留所有权利。
Shear-wave polarization anisotropy in the central part of northeastern (NE) Japan was investigated. We analyzed S phases of 293 intermediate-depth earthquakes recorded at 77 stations and obtained 1286 splitting parameters. The obtained results show the systematic variation in splitting parameters across the arc. The leading shear-wave polarization directions (fast direction) obtained at stations in the western side of the study area are oriented nearly E-W, which is sub-parallel to the direction of relative plate motion between the Pacific plate and the North American/Okhotsk plate. In contrast, fast directions obtained at stations in the eastern side of the study area are oriented approximately N-S. Stations in the western side have a larger average delay time compared to those in the eastern side. These variations suggest that the nature of anisotropy is quite different between the eastern and the western sides. Both experimental studies on the deformation of olivine and numerical simulations of plate-driven flow predict that the lattice-preferred orientation of olivine causes the fast direction sub-parallel to the flow direction for the conditions in the mantle wedge of NE Japan. We thus infer that the lattice-preferred orientation of olivine generated by flow-induced strain is the most likely candidate for anisotropy that produces splitting with E-W fast direction. Three possible causes of anisotropy in the eastern side are considered: deformation of water-rich olivine in the mantle wedge, trench-parallel flow in the mantle wedge due to along-strike dip variations in the slab and anisotropy in the crust and the slab. We could not, however, determine which causes are dominant. Further systematic study is required to reveal the cause of anisotropy in the eastern side. (C) 2004 Elsevier B.V. All rights reserved.