Estimate of the Rigidity of Eclogite in the Lower Mantle From Waveform Modeling of Broadband S -to- P Wave Conversions: RIGIDITY OF ECLOGITE FROM SP CONVERSIONS
Estimate of the Rigidity of Eclogite in the Lower Mantle From Waveform Modeling of Broadband S -to- P Wave Conversions: RIGIDITY OF ECLOGITE FROM SP CONVERSIONS
复制标题
根据宽带 S 波到 P 波转换的波形建模估计下地幔中榴辉岩的刚性：SP 转换中的榴辉岩的刚性
DOI：
10.1002/2017gl075463
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发表时间：
2017
影响因子：
5.2
通讯作者：
Thorne, Michael S.
中科院分区：
文献类型：
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作者：
Haugland, Samuel M.;Ritsema, Jeroen;Kaneshima, Satoshi;Thorne, Michael S.
2007年7月21日巴西西部地震（Mw=6.0，深度= 633 km）的宽带USArray记录包括在pwave到达后约40秒、75秒和100秒的高振幅信号。它们与南美洲西北部地幔的波对波转换是一致的。根据倾斜叠加和相似分析，100 s处的信号为asS1750P，振幅最大，形成于1750 km深度。利用轴对称、有限差分合成的波形模型表明，s1750p3是由10 km厚的非均质层产生的，可能是下地幔中洋中脊玄武岩的俯冲碎片。s1750pi的负极性是一个强有力的观测结果，限制了剪切速度异常δ v的非均质性为负。s1750p的振幅表明δ vsi在−1.6% ~−12.4%之间。由于记录的ds1750p振幅的大变异性和s1750p波形建模的简化，δ vsi的不确定性很大。我们对δ vsi估计的下限与Tsuchiya（2011）的从头计算一致，他估计下地幔压力下的δ vsi在0到- 2%之间，这是由于后闪辉石相变的剪切软化。
Broadband USArray recordings of the 21 July 2007 western Brazil earthquake (Mw=6.0; depth = 633 km) include high‐amplitude signals about 40 s, 75 s, and 100 s after thePwave arrival. They are consistent withSwave toPwave conversions in the mantle beneath northwestern South America. The signal at 100 s, denoted asS1750P, has the highest amplitude and is formed at 1,750 km depth based on slant‐stacking and semblance analysis. Waveform modeling using axisymmetric, finite difference synthetics indicates thatS1750Pis generated by a 10 km thick heterogeneity, presumably a fragment of subducted mid‐ocean ridge basalt in the lower mantle. The negative polarity ofS1750Pis a robust observation and constrains the shear velocity anomalyδVSof the heterogeneity to be negative. The amplitude ofS1750Pindicates thatδVSis in the range from −1.6% to −12.4%. The large uncertainty inδVSis due to the large variability in the recordedS1750Pamplitude and simplifications in the modeling ofS1750Pwaveforms. The lower end of our estimate forδVSis consistent with ab initio calculations by Tsuchiya (2011), who estimated thatδVSof eclogite at lower mantle pressure is between 0 and −2% due to shear softening from the poststishovite phase transition.