Measuring the seismic velocity in the top 15 km of Earth’s inner core

Godwin, Harriet, Waszek, Lauren, and Deuss, Arwen (2018) Measuring the seismic velocity in the top 15 km of Earth’s inner core. Physics of the Earth and Planetary Interiors, 274. pp. 158-169.

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Abstract

We present seismic observations of the uppermost layer of the inner core. This was formed most recently, thus its seismic features are related to current solidification processes. Previous studies have only constrained the east-west hemispherical seismic velocity structure in the Earth’s inner core at depths greater than 15 km below the inner core boundary. The properties of shallower structure have not yet been determined, because the seismic waves PKIKP and PKiKP used for differential travel time analysis arrive close together and start to interfere. Here, we present a method to make differential travel time measurements for waves that turn in the top 15 km of the inner core, and measure the corresponding seismic velocity anomalies. We achieve this by generating synthetic seismograms to model the overlapping signals of the inner core phase PKIKP and the inner core boundary phase PKiKP. We then use a waveform comparison to attribute different parts of the signal to each phase. By measuring the same parts of the signal in both observed and synthetic data, we are able to calculate differential travel time residuals. We apply our method to data with ray paths which traverse the Pacific hemisphere boundary. We generate a velocity model for this region, finding lower velocity for deeper, more easterly ray paths. Forward modelling suggests that this region contains either a high velocity upper layer, or variation in the location of the hemisphere boundary with depth and/or latitude. Our study presents the first direct seismic observation of the uppermost 15 km of the inner core, opening new possibilities for further investigating the inner core boundary region.

Item ID: 65367
Item Type: Article (Research - C1)
ISSN: 1872-7395
Keywords: seismology, body waves, inner core
Copyright Information: © 2017 Elsevier B.V. All rights reserved.
Funders: Natural Environment Research Council Doctoral Training Partnership in Environmental Research at the University of Oxford (UO), Australian Government (AG), European Research Council (ERC), Netherlands Organization for Scientific Research (NWO), Ammodo-KNAW (AK)
Projects and Grants: UO award number NE/L002612/1, AG Discovery Early Career Research Award project number DE170100329, ERC European Union’s Horizon 2020 research and innovation programme, grant agreement No. 681535 ATUNE, NWO Vici award number 016.160.310/526, AK award in Natural Sciences
Date Deposited: 20 Dec 2020 21:15
FoR Codes: 37 EARTH SCIENCES > 3706 Geophysics > 370609 Seismology and seismic exploration @ 100%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 100%
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