Seismic anisotropy of the lithosphere/asthenosphere system beneath the Rwenzori region of the Albertine Rift
Seismic anisotropy of the lithosphere/asthenosphere system beneath the Rwenzori region of the Albertine Rift
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阿尔伯丁裂谷鲁文佐里地区岩石圈/软流圈系统的地震各向异性
DOI：
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发表时间：
2016
影响因子：
2.3
通讯作者：
G. Rümpker
中科院分区：
文献类型：
--
作者：
B. Homuth;U. Löbl;A. Batte;K. Link;C. Kasereka;G. Rümpker
本文利用当地地震和大地震的剪切波分裂测量结果研究了东非裂谷系鲁文佐里地区上地幔的地震各向异性。在大多数台站，从单个地震中获得的剪切波分裂参数只表现出与后方位角的微小变化。因此，我们采用SKS波形的联合反演来推导假设的单层参数。相应的快极化一般是裂缝平行的，平均延迟时间约为1 s。地壳内局部事件的剪切相的特点是平均延迟时间为0.04秒。局部地幔地震的延迟时间在0.2秒的范围内。这一观测结果表明，裂谷下方地震各向异性的主要源区位于地幔内。我们使用有限频率波形模拟测试不同的模型的岩石圈/软流圈系统的裂谷内的各向异性。结果表明，裂谷平行的快速极化是一致的水平横向各向同性（HTI各向异性）所造成的裂谷平行岩浆侵入体或透镜体位于岩石圈地幔，因为它会被预期在大陆裂谷的早期阶段。此外，在研究区域的南部观察到的快速极化的短尺度空间变化可以解释的效果，由于沉积盆地的各向同性速度低，结合在上地幔各向异性织物的方向的转变。一个均匀的各向异性层与大规模的软流圈地幔流是不太一致的观测分裂参数。
Shear-wave splitting measurements from local and teleseismic earthquakes are used to investigate the seismic anisotropy in the upper mantle beneath the Rwenzori region of the East African Rift system. At most stations, shear-wave splitting parameters obtained from individual earthquakes exhibit only minor variations with backazimuth. We therefore employ a joint inversion of SKS waveforms to derive hypothetical one-layer parameters. The corresponding fast polarizations are generally rift parallel and the average delay time is about 1 s. Shear phases from local events within the crust are characterized by an average delay time of 0.04 s. Delay times from local mantle earthquakes are in the range of 0.2 s. This observation suggests that the dominant source region for seismic anisotropy beneath the rift is located within the mantle. We use finite-frequency waveform modeling to test different models of anisotropy within the lithosphere/asthenosphere system of the rift. The results show that the rift-parallel fast polarizations are consistent with horizontal transverse isotropy (HTI anisotropy) caused by rift-parallel magmatic intrusions or lenses located within the lithospheric mantle—as it would be expected during the early stages of continental rifting. Furthermore, the short-scale spatial variations in the fast polarizations observed in the southern part of the study area can be explained by effects due to sedimentary basins of low isotropic velocity in combination with a shift in the orientation of anisotropic fabrics in the upper mantle. A uniform anisotropic layer in relation to large-scale asthenospheric mantle flow is less consistent with the observed splitting parameters.
影响因子：
5.3
作者：
I. Wölbern;U. Löbl;G. Rümpker
通讯作者：
I. Wölbern;U. Löbl;G. Rümpker