Locating scatterers in the mantle using array analysis of PKP precursors from an earthquake doublet
Locating scatterers in the mantle using array analysis of PKP precursors from an earthquake doublet
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DOI：
10.1016/j.epsl.2006.12.002
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发表时间：
2007-03
影响因子：
5.3
通讯作者：
A. Cao;B. Romanowicz
中科院分区：
文献类型：
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作者：
A. Cao;B. Romanowicz
在耶洛奈夫地震台阵（YK）观测到的高质量成对地震的分离良好的单个PKP前兆，为研究相应散射体的位置和评估位置估计的稳定性提供了机会。基于叠加的单个前兆和PKIKP相位的波形的比较，我们能够确定这些前兆中的大多数起源于接收侧上的B焦散线上方的PKPbc（而不是PKPab）分支的散射。这使得在下地幔中的散射体的可靠位置。它们的深度范围从2890 km（CMB）到2270 km，散射角范围从45.8 °到16.0 °，表面投影范围从加拿大安大略南部到北方萨斯喀彻温省北部。这些位置与地幔层析成像模型中从慢到快的速度过渡有关，并遵循北美化石板的预期一般倾角方向。这表明，在北美洲下面的俯冲板片残留物保留了它们的成分特征。我们基本上可以把这些散射体看作是平面边界的反射，这一事实表明板片的残余碎片可能在空间上延伸，这应该用宽带数据来证实。在测得的慢度和后方位角的双峰前体的平均差异小至0.08秒/度和1.4度，分别。我们的研究表明，它可能会找到这样的散射体使用单次地震和小孔径地震台阵。
Well separated individual PKP precursors observed at the Yellowknife seismic array (YK) for a high quality doublet of earthquakes provide an opportunity to study the location of the corresponding scatterers and assess the stability of the location estimation. Based on the comparison of the waveforms of stacked individual precursors and those of PKIKP phases, we are able to determine that most of these precursors originate from scattering of the PKPbc (rather than the PKPab) branch above the B caustic on the receiver side. This allows a reliable location of the scatterers in the lower mantle. Their depths range from 2890 km (the CMB) to 2270 km, scattering angles range from 45.8° to 16.0°, and surface projections range from southern Ontario to northern Saskatchewan in Canada. These locations are associated with transitions from slow to fast velocities in mantle tomographic models and follow the expected general dip direction of fossil slabs under north America. This suggests that the subducted slab remnants under north America have retained their compositional signature. The fact that we can essentially treat these scatterers as reflections from plane boundaries suggests that the remnant fragments of slab may be spatially extended, which should be confirmed using broadband data. Average differences in measured slowness and back-azimuth of the doublet precursors are as small as 0.08 s/deg and 1.4 deg, respectively. Our study indicates that it may be possible to locate such scatterers using single earthquakes and small aperture seismic arrays.