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首页> 外文期刊>Physics of the Earth and Planetary Interiors: A Journal Devoted to Obsevational and Experimerntal Studies of the Chemistry and Physics of Planetary Interiors and Their Theoretical Interpretation >Distinct velocity variations around the base of the upper mantle beneath northeast Asia
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Distinct velocity variations around the base of the upper mantle beneath northeast Asia

机译：东北亚下方上地幔底部周围明显的速度变化

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Both the global and regional P wave tomographic Studies have revealed significant deep Structural heterogeneities in subduction zone regions. In particular, low-velocity anomalies have been observed beneath the descending high-velocity slabs in a number of subduction zones. The limited resolution at large depths and possible trade-off between the high and low velocities, however, make it difficult to Substantiate this feature and evaluate the vertical extent of the low-velocity Structure. From broadband waveform modeling of triplicated phases near the 660-km discontinuity for three deep events, we constrained both the P and SH wave velocity Structures around the base of the upper mantle in northeast Asia. For the two events beneath the Southern Kurile, the rays traveled through the lowermost transition zone and uppermost lower mantle under the descending Pacific slab. Out preferred models consistently Suggest normal-to-lower P and significantly low SH velocities above and below the 660-km discontinuity extending to about 760-km depth compared with the global IASP91 model, corroborating previous observations for a slow structure underneath the slab. In contrast, both high P and SH velocity anomalies are shown in our preferred models for the Japan subduction zone region, likely reflecting the Structural feature of a slab stagnant above the 660-km discontinuity. The velocity JUMPS across the 660-km discontinuity were found to be on average 4.5% and 7% for P and S waves under the South Kurile, and 3% and 6% under the Japan subduction zone. The respective velocity contrasts in the two regions are consistent with mineralogical models for colder slab interior and hotter under-slab areas. Based on mineral physics data, the depth-averaged similar to 1.5% P and similar to 2.5% SH velocity differences in the depth range of 560-760 km between the two regions Could be primarily explained by a 350-450 K temperature variation, although the presence of about 0.5-1 wt.% water might also contribute to the Subtle velocity variations near the base of the transition zone in the Southern Kurile. From our modeling results, we speculate that the Slow Structure in the Southern Kurile may be Correlated to the low-velocity zone observed previously around the 410-km discontinuity Under Northern Honshu. If this is the case, both may be associated with a thermal anormaly rooted in the lower mantle beneath the subduction zone in northeast Asia.
机译：全球和区域P波层析成像研究都显示出俯冲带区域存在明显的深层结构异质性。特别是，在许多俯冲带中，在下降的高速板下方观察到了低速异常。然而，在大深度上有限的分辨率以及高速和低速之间可能的取舍，使得难以证实该特征并难以评估低速结构的垂直范围。通过对三个深部事件在660 km不连续附近的三重相位的宽带波形建模，我们限制了东北亚上地幔底部周围的P波和SH波速度结构。对于南部千岛山脉下方的两个事件，光线穿过下降的太平洋板块下方的最低过渡区和最高地幔。与全球IASP91模型相比，首选模型始终建议在660 km不连续点之上和之下的P正常到较低的P和SH速度低，延伸到大约760 km的深度，这证实了以前对板下面缓慢结构的观察。相反，我们在日本俯冲带地区的首选模型中同时显示了高P和SH速度异常，这很可能反映了在660公里不连续面上方停滞的平板的结构特征。在南千岛下，沿P和S波的660 km不连续处的速度JUMPS平均为4.5％和7％，在日本俯冲带下为3％和6％。这两个区域的速度对比与较冷的板坯内部和较热的板坯下部区域的矿物学模型一致。根据矿物物理数据，两个区域之间在560-760 km深度范围内的平均深度相似于1.5％P和相似于2.5％SH速度差可以主要由350-450 K温度变化来解释大约0.5-1 wt。％的水的存在也可能导致南千岛南部过渡区底部附近的微妙速度变化。根据我们的模拟结果，我们推测南部千岛地区的慢速构造可能与先前在本州北部410公里间断处附近观测到的低速带有关。如果是这种情况，两者都可能与根源于东北亚俯冲带下方下地幔的热异常有关。

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