Uppermost Inner Core Heterogeneity from Differential Travel Times of PKIKP vs. PKP-Bdiff and PKP-Cdiff Phases

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• 作者：Marian Ivan ; Xiaobo He
• 关键词：Uppermost inner core ; diffracted PKP phases ; PKIKP ; inner core heterogeneity
• 刊名：Pure and Applied Geophysics
• 出版年：2017
• 出版时间：January 2017
• 年：2017
• 卷：174
• 期：1
• 页码：249-259
• 全文大小：
• 刊物类别：Earth and Environmental Science
• 刊物主题：Geophysics/Geodesy;
• 出版者：Springer International Publishing
• ISSN：1420-9136
• 卷排序：174

文摘

We evaluate the average P-wave velocity perturbations of the Earth’s uppermost inner core (IC) by analyzing two pairs of core phases: PKIKP–PKP-Bdiff (456 observations in the distance range of 138.5°–142°) and PKIKP–PKP-Cdiff (1215 observations at 155°–162°). The former is most sensitive to inner core velocities in the depth range of 350–590 km and the latter from 0 to 100 km below the inner core boundary. The differential travel-time residuals exhibit the roughly “east–west” hemispheric pattern especially beneath the Pacific Ocean. Here, the separation between the two quasi-hemispheres is near the 150°W meridian (from PKP-Bdiff observations), but possibly rotated toward a NW–SE orientation, from PKP-Cdiff. Alternately, a velocity heterogeneity could be present here, in agreement with the previously reported PKIKP vs. PKP_BC observations. Assuming the conventional definition for the IC quasi-hemispheres (i.e., the QEH between 0° and 180°E, and the QWH between 0° and 180°W), the quasi-Eastern hemisphere exhibits perturbations of (+1.17 ± 0.04) % (from PKIKP–PKP-Bdiff) and (+0.19 ± 0.01) % (from PKIKP–PKP-Cdiff). The corresponding perturbations in the quasi-Western hemisphere are of (−0.06 ± 0.06) % and (−0.19 ± 0.02) %, respectively. An anomalous IC zone beneath the Indian Ocean is not conspicuous in our PKIKP–PKP-Cdiff observations. Beneath the North Atlantic, the separation between the IC quasi-hemispheres appears to be located between 60°W and 30°W from the PKP-Bdiff observations, but it remains unresolved from the PKP-Cdiff data, due to scarce observations here.