Inner core structure behind the PKP core phase triplication

Blom, Nienke A., Deuss, Arwen, Paulssen, Hanneke, and Waszek, Lauren (2015) Inner core structure behind the PKP core phase triplication. Geophysical Journal International, 201 (3). pp. 1657-1665.

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Abstract

The structure of the Earth's inner core is not well known between depths of ∼100–200 km beneath the inner core boundary. This is a result of the PKP core phase triplication and the existence of strong precursors to PKP phases, which hinder the measurement of inner core compressional PKIKP waves at epicentral distances between roughly 143 and 148°. Consequently, interpretation of the detailed structure of deeper regions also remains difficult. To overcome these issues we stack seismograms in slowness and time, separating the PKP and PKIKP phases which arrive simultaneously but with different slowness. We apply this method to study the inner core's Western hemisphere beneath South and Central America using paths travelling in the quasi-polar direction between 140 and 150° epicentral distance, which enables us to measure PKiKP–PKIKP differential traveltimes up to greater epicentral distance than has previously been done. The resulting PKiKP–PKIKP differential traveltime residuals increase with epicentral distance, which indicates a marked increase in seismic velocity for polar paths at depths greater than 100 km compared to reference model AK135. Assuming a homogeneous outer core, these findings can be explained by either (i) inner core heterogeneity due to an increase in isotropic velocity or (ii) increase in anisotropy over the studied depth range. Although this study only samples a small region of the inner core and the current data cannot distinguish between the two alternatives, we prefer the latter interpretation in the light of previous work.

Item ID: 65370
Item Type: Article (Research - C1)
ISSN: 1365-246X
Keywords: Core, outer core and inner core; Body waves; Seismic anisotropy
Copyright Information: © The Authors 2015. Published by Oxford University Press on behalf of The Royal Astronomical Society.
Funders: European Commission (EC), Netherlands Organisation for Scientific Research (NWO), European Research Council (ERC), Leverhulme Trust (LT), Homerton College (HC)
Projects and Grants: EC Erasmus placement scholarship, NWO VIDI grant no. 864.11.008, ERC European Community’s Seventh Framework Programme (FP7/2007–2013)/ERC grant 204995., LT Phillip Leverhulme Prize, HC Research Fellowship
Date Deposited: 06 Jan 2021 23:56
FoR Codes: 04 EARTH SCIENCES > 0404 Geophysics > 040407 Seismology and Seismic Exploration @ 100%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 100%
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