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Array-based iterative measurements of SmKS travel times and their constraints on outermost core structure

Wu, Wenbo and Irving, Jessica C. E. (2020) Array-based iterative measurements of SmKS travel times and their constraints on outermost core structure. Journal of Geophysical Research. Solid Earth, 125 (3). Art. No. e2019JB018162. ISSN 2169-9313. https://resolver.caltech.edu/CaltechAUTHORS:20200213-132705776

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Abstract

Vigorous convection in Earth's outer core led to the suggestion that it is chemically homogeneous. However, there is increasing seismic evidence for structural complexities close to the outer core's upper and lower boundaries. Both body waves and normal mode data have been used to estimate a P wave velocity, V_p, at the top of the outer core (the E’ layer), which is lower than that in the Preliminary Reference Earth Model. However, these low V_p models do not agree on the form of this velocity anomaly. One reason for this is the difficulty in retrieving and measuring SmKS arrival times. To address this issue, we propose a novel approach using data from seismic arrays to iteratively measure SmKS-SKKS-differential travel times. This approach extracts individual SmKS signal from mixed waveforms of the SmKS series, allowing us to reliably measure differential travel times. We successfully use this method to measure SmKS time delays from earthquakes in the Fiji‐Tonga and Vanuatu subduction zones. SmKS time delays are measured by waveform cross correlation between SmKS and SKKS, and the cross‐correlation coefficient allows us to access measurement quality. We also apply this iterative scheme to synthetic SmKS seismograms to investigate the 3‐D mantle structure's effects. The mantle structure corrections are not negligible for our data, and neglecting them could bias the V_p estimation of uppermost outer core. After mantle structure corrections, we can still see substantial time delays of S3KS, S4KS, and S5KS, supporting a low V_p at the top of Earth's outer core.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1029/2019jb018162DOIArticle
ORCID:
AuthorORCID
Wu, Wenbo0000-0002-6249-8065
Irving, Jessica C. E.0000-0002-0866-8246
Additional Information:© 2020 American Geophysical Union. Received 6 JUN 2019; Accepted 11 FEB 2020; Accepted article online 12 FEB 2020. We acknowledge support from the NSF (EAR1644399 and 1736046). The authors thank J. Ristema and C. A. Moreno Chaves for their code to calculate ray theoretical times through S40RTS. The authors acknowledge the use of the GMT (Wessel & Smith, 1998) and SAC (Goldstein et al., 2003) software packages. Waveform data have been collected using the Python toolbox ObsPy (Beyreuther et al., 2010). The waveform data used in this study are from the following networks: 722 AC, AF (doi:10.7914/SN/AF), BA, BE (doi:10.7914/SN/BE), BL, BN, BS (doi:10.7914/SN/BS), BW (doi:10.7914/SN/BW), C, C1 (doi:10.7914/SN/C1), CA (doi:10.7914/SN/CA), CB (doi:10.7914/SN/CB), CH (doi:10.12686/sed/networks/ch), CM, CN (doi:10.7914/SN/CN), CR, CU (doi:10.7914/SN/CU), CX (doi:10.14470/PK615318), CZ (doi:10.7914/SN/CZ), DK, DR (doi:10.7914/SN/DR), DZ, EB, EE, EI (doi:10.7914/SN/EI), FN, FR (doi:10.15778/RESIF.FR), G (doi:10.18715/GEOSCOPE.G), GB, GE (doi:10.14470/TR560404), GR, GS (doi:10.7914/SN/GS), GT (doi:10.7914/SN/GT), GU (doi:10.7914/SN/GU), HE (doi:10.14470/UR044600), HL (doi:10.7914/SN/HL), HT (doi:10.7914/SN/HT), HU (doi:10.14470/UH028726), IB (doi:10.7914/SN/IB), II(doi:10.7914/SN/II), IM, IP, IS, IU(doi:10.7914/SN/IU), IV (doi:10.13127/SD/X0FXnH7QfY), KC (doi:10.7914/SN/KC), KN, KO (doi:10.7914/SN/KO), KP (doi:10.7914/SN/KP), KR (doi:10.7914/SN/KR), KW, KZ (doi:10.7914/SN/KZ), LD, LI (doi:10.7914/SN/LI), LX, MC, MD (doi:10.7914/SN/MD), MN (doi:10.13127/SD/fBBBtDtd6q), MX (doi:10.21766/SSNMX/SN/MX), N4 (doi:10.7914/SN/N4), NA (doi:10.21944/da7a3f‐7e3a‐3b33‐a436‐516a01b6af3f ), NE (doi:10.7914/SN/NE), NI (doi:10.7914/SN/NI), NJ (doi:10.7914/SN/NJ), NL (doi:10.21944/e970fd34‐ 23b9‐3411‐b366‐e4f72877d2c5), NM, NO, NR (doi:10.7914/SN/NR), NU (doi:10.7914/SN/NU), OE (doi:10.7914/SN/OE), OV, OX (doi:10.7914/SN/OX), PE (doi:10.7914/SN/PE), PL, PM, PR (doi:10.7914/SN/PR), PZ (doi:10.7914/SN/PZ), RD (doi:10.15778/RESIF.RD), RO (doi:10.7914/SN/RO), SI, SJ, SK (doi:10.14470/FX099882), SL (doi:10.7914/SN/SL), SP (doi:10.7914/SN/SP), SS, SV, SX (doi:10.7914/SN/SX), TA (doi:10.7914/SN/TA), TH (doi:10.7914/SN/TH), TR, TT, TU, UK, UP (doi:10.18159/SNSN), US (doi:10.7914/SN/US), VE, VI, WC, WI (doi: doi:10.18715/antilles.WI), WM (doi:10.14470/JZ581150), X5, X6 (doi:10.7914/SN/X6 2007), X7 (doi:10.15778/RESIF.X72010), XB (doi:10.7914/SN/XB 2009), XE (doi:10.7914/SN/XE 2009), XI (doi:10.7914/SN/XI 2011), XJ (doi:10.12686/sed/networks/xh), XK (doi:10.7914/SN/XK 2012), XN (doi:10.7914/SN/XN 2008), XO (doi:10.7914/SN/XO 2011), XQ (doi:10.7914/SN/XQ 2012), XT (doi:10.7914/SN/XT 2003), XV (doi:10.7914/SN/XV 2011), XW (doi:10.15778/RESIF.XW2007 and doi:10.7914/SN/XW 2009), XY (doi:10.15778/RESIF.XY2007 and doi:10.7914/SN/XY 2010), XZ (doi:10.7914/SN/XZ 2003), Y1, Y4 (doi:10.15778/RESIF.Y42004), YB (doi:10.15778/RESIF.YB2000 and doi:10.7914/SN/YB 2013), YD, YF, YG, YH (doi:10.7914/SN/YH 2012), YI (doi:10.7914/SN/YI 2003 and doi:10.15778/RESIF.YI2008), YJ, YK, YO (doi:10.7914/SN/YO 2014), YP, YQ (doi:10.7914/SN/YQ 2013), YR (doi:10.15778/RESIF.YR1999), YS (doi:10.7914/SN/YS 2009), YV, YW, YY, YZ (doi:10.7914/SN/YZ 2009), Z4 (doi:10.7914/SN/Z4 2009), Z9 (doi:10.7914/SN/Z9 2010), ZA, ZC (doi:10.7914/SN/ZC 2013), ZD (doi:10.7914/SN/ZD 2010), ZE (doi:10.7914/SN/ZE 2007), ZF, ZG (doi:10.7914/SN/ZG 2010), ZH (doi:10.15778/RESIF.ZH2003), ZL (doi:10.7914/SN/ZL 2007), ZN, ZO (doi:10.7914/SN/ZO 2010), ZP, ZR, ZS, ZT (doi:10.7914/SN/ZT 2015), ZU, ZV, ZX, ZZ (doi:10.14470/MM7557265463), 1E, 4F, 6D, 6E, 7A (doi:10.7914/SN/7A 2013), 7C (doi:10.15778/RESIF.7C2009), 7E (doi:10.14470/2R383989), and 7J, 8A, 9D (doi:10.7914/SN/9A 2012). (n.d.).
Group:Seismological Laboratory
Funders:
Funding AgencyGrant Number
NSFEAR-1644399
NSFEAR-1736046
Subject Keywords:Outer core; SmKS body waves
Issue or Number:3
Record Number:CaltechAUTHORS:20200213-132705776
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20200213-132705776
Official Citation:Wu, W., & Irving, J. C. E. ( 2020). Array‐based iterative measurements of SmKS travel times and their constraints on outermost core structure. Journal of Geophysical Research: Solid Earth, 125, e2019JB018162. https://doi.org/10.1029/2019JB018162
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:101275
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:13 Feb 2020 21:34
Last Modified:23 Mar 2020 14:57

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