Tomography of crust and lithosphere in the western Indian Ocean from noise cross-correlations of land and ocean bottom seismometers
Tomography of crust and lithosphere in the western Indian Ocean from noise cross-correlations of land and ocean bottom seismometers
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DOI：
10.1093/gji/ggz333
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发表时间：
2019-07
影响因子：
2.8
通讯作者：
Sarah Hable;K. Sigloch;É. Stutzmann;S. Kiselev;G. Barruol
中科院分区：
文献类型：
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作者：
Sarah Hable;K. Sigloch;É. Stutzmann;S. Kiselev;G. Barruol
我们利用地震噪声互相关得到了西印度洋以下大洋地壳和最上地幔深度范围内SV波速度的三维层析模型。研究区域位于马达加斯加和印度洋三个扩张海脊之间，以留尼汪岛火山热点为中心，面积为2000×2000平方公里。我们使用了Rhum-Rum项目部署的38个海底地震仪(OBS)以及位于留尼汪岛、马达加斯加、毛里求斯、罗德里格斯和特罗梅林的10个岛屿台站的地震图。计算了1119个OBS-OBS、陆地-OBS和陆地-陆地站对的相位互相关，一个相位加权叠加算法在3-50 S的周期范围内产生了稳健的群速度测量。我们证明，对于大规模的海洋盆地层析成像，站间2000公里的OBS相关具有足够高的质量。许多OBS产生了与陆地站类似的良好的群速度测量结果。除了瑞利波以外，噪声关联还包括一种低速波型，传播距离超过1000公里，传播距离为0.81.5公里的S−1，推测为穿过海底沉积物的肖尔特波。选择了100条最高质量的群速度曲线，用于地壳和岩石圈深度的层析反演。这次反演是与一组来自地震的较长周期、瑞雷波相位和群速度测量的数据集一起进行的，这些数据集以前得到了印度洋岩石圈和软流层的三维模型。稳健的分辨率测试和在30公里以上可信的结构发现证实了利用噪声衍生的OBS相关性将地壳结构添加到海洋地幔的地震衍生层析成像中。相对于地壳参考模型CRUST1.0，我们的新剪切速度模型倾向于同时增强慢异常和快异常。它揭示了毛里求斯留尼汪岛、马达加斯加罗德里格斯海脊和中印度扩张海脊下20公里深处的缓慢异常。这些构造显然与地壳厚度增加和/或火山活动有关。留尼汪岛和毛里求斯的局部地壳增厚可能与该热点的岩浆底侵作用有关。此外，这些岛屿的特点是岩石圈增厚，这可能反映了地壳在源头熔融的枯竭、脱水的地幔区域。我们的断层扫描模型是作为电子补充提供的。
We use seismic noise cross-correlations to obtain a 3-D tomography model of SV-wave velocities beneath the western Indian Ocean, in the depth range of the oceanic crust and uppermost mantle. The study area covers 2000 × 2000 km2 between Madagascar and the three spreading ridges of the Indian Ocean, centred on the volcanic hotspot of La Réunion. We use seismograms from 38 ocean bottom seismometers (OBSs) deployed by the RHUM-RUM project and 10 island stations on La Réunion, Madagascar, Mauritius, Rodrigues, and Tromelin. Phase cross-correlations are calculated for 1119 OBS-to-OBS, land-to-OBS, and land-to-land station pairs, and a phase-weighted stacking algorithm yields robust group velocity measurements in the period range of 3–50 s. We demonstrate that OBS correlations across large interstation distances of >2000 km are of sufficiently high quality for large-scale tomography of ocean basins. Many OBSs yielded similarly good group velocity measurements as land stations. Besides Rayleigh waves, the noise correlations contain a low-velocity wave type propagating at 0.8–1.5 km s−1 over distances exceeding 1000 km, presumably Scholte waves travelling through seafloor sediments. The 100 highest-quality group velocity curves are selected for tomographic inversion at crustal and lithospheric depths. The inversion is executed jointly with a data set of longer-period, Rayleigh-wave phase and group velocity measurements from earthquakes, which had previously yielded a 3-D model of Indian Ocean lithosphere and asthenosphere. Robust resolution tests and plausible structural findings in the upper 30 km validate the use of noise-derived OBS correlations for adding crustal structure to earthquake-derived tomography of the oceanic mantle. Relative to crustal reference model CRUST1.0, our new shear-velocity model tends to enhance both slow and fast anomalies. It reveals slow anomalies at 20 km depth beneath La Réunion, Mauritius, Rodrigues Ridge, Madagascar Rise, and beneath the Central Indian spreading ridge. These structures can clearly be associated with increased crustal thickness and/or volcanic activity. Locally thickened crust beneath La Réunion and Mauritius is probably related to magmatic underplating by the hotspot. In addition, these islands are characterized by a thickened lithosphere that may reflect the depleted, dehydrated mantle regions from which the crustal melts where sourced. Our tomography model is available as electronic supplement.