【摘要】 为了深入了解日本东北俯冲带的地震构造及火山活动,利用布设在日本列岛上密集地震台网所记录到的高质量浅震及深震到时数据,反演求得了该区域地壳及上地幔的三维P波和S波速度结构。为了最大程度地利用地震数据提取模型空间中更为精细的速度结构信息,采用不规则网格模型采进行地震层析成像反演。所得的高分辨率成像结果清晰地显示,2008年岩手地震(M 7.2)位于高低速异常的转换区,而且震源区的地壳介质非均匀性极强。在震源区的下地壳及上地幔顶部存在着明显的低速异常,可能代表了岛弧岩浆和流体在该深度处的储集。研究结果表明,2008年岩手地震的产生受到了来自上地幔楔的岩浆和流体的影响,且这些岩浆和流体与俯冲太平洋板块的脱水作用有着密切的联系。更多还原

【Abstract】 To better understand the seismotectonics and arc magmatism in the Northeast Japan subduction zone,we studied high-resolution 3-D P-and S-wave velocity structures of the crust and upper mantle under this region using a large number of high-quality arrival-time data from the local shallow and intermediate-depth earthquakes recorded by the high-sensitivity seismic network installed on the Japan Islands.We adopt an irregular-grid parameterization to conduct the tomographic inversion in order to extract more useful information from the data used.Our results show that the mainshock of the 2008 Iwate-Miyagi earthquake (M 7.2) was located in a boundary zone where seismic velocity changed dramatically,indicating that the crustal medium in the source area is very heterogeneous.A pronounced low-velocity anomaly is revealed in the lower crust and uppermost mantle under the mainshock hypocenter,which may reflect the arc magma and fluids ascending from the upper-mantle wedge released by the dehydration process of the subducting Pacific slab.The fluids and arc magma may have influenced the nucleation and rupture process of the large crustal earthquakes.更多还原