TY - JOUR
T1 - Array-Based Iterative Measurements of SmKS Travel Times and Their Constraints on Outermost Core Structure
AU - Wu, Wenbo
AU - Irving, Jessica C.E.
N1 - Funding Information:
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, ) and SAC (Goldstein et al., ) software packages. Waveform data have been collected using the Python toolbox ObsPy (Beyreuther et al., ). 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.).
Funding Information:
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,) and SAC (Goldstein et al.,) software packages. Waveform data have been collected using the Python toolbox ObsPy (Beyreuther et al.,). 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.).
Publisher Copyright:
© 2020. American Geophysical Union. All Rights Reserved.
PY - 2020/3/1
Y1 - 2020/3/1
N2 - 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 (Formula presented.) wave velocity, (Formula presented.), at the top of the outer core (the (Formula presented.) layer), which is lower than that in the Preliminary Reference Earth Model. However, these low (Formula presented.) models do not agree on the form of this velocity anomaly. One reason for this is the difficulty in retrieving and measuring (Formula presented.) arrival times. To address this issue, we propose a novel approach using data from seismic arrays to iteratively measure (Formula presented.) - (Formula presented.) differential travel times. This approach extracts individual (Formula presented.) signal from mixed waveforms of the (Formula presented.) series, allowing us to reliably measure differential travel times. We successfully use this method to measure (Formula presented.) time delays from earthquakes in the Fiji-Tonga and Vanuatu subduction zones. (Formula presented.) time delays are measured by waveform cross correlation between (Formula presented.) and (Formula presented.), and the cross-correlation coefficient allows us to access measurement quality. We also apply this iterative scheme to synthetic (Formula presented.) 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 (Formula presented.) estimation of uppermost outer core. After mantle structure corrections, we can still see substantial time delays of (Formula presented.), (Formula presented.), and (Formula presented.), supporting a low (Formula presented.) at the top of Earth's outer core.
AB - 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 (Formula presented.) wave velocity, (Formula presented.), at the top of the outer core (the (Formula presented.) layer), which is lower than that in the Preliminary Reference Earth Model. However, these low (Formula presented.) models do not agree on the form of this velocity anomaly. One reason for this is the difficulty in retrieving and measuring (Formula presented.) arrival times. To address this issue, we propose a novel approach using data from seismic arrays to iteratively measure (Formula presented.) - (Formula presented.) differential travel times. This approach extracts individual (Formula presented.) signal from mixed waveforms of the (Formula presented.) series, allowing us to reliably measure differential travel times. We successfully use this method to measure (Formula presented.) time delays from earthquakes in the Fiji-Tonga and Vanuatu subduction zones. (Formula presented.) time delays are measured by waveform cross correlation between (Formula presented.) and (Formula presented.), and the cross-correlation coefficient allows us to access measurement quality. We also apply this iterative scheme to synthetic (Formula presented.) 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 (Formula presented.) estimation of uppermost outer core. After mantle structure corrections, we can still see substantial time delays of (Formula presented.), (Formula presented.), and (Formula presented.), supporting a low (Formula presented.) at the top of Earth's outer core.
KW - SmKS body waves
KW - outer core
UR - http://www.scopus.com/inward/record.url?scp=85082333044&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85082333044&partnerID=8YFLogxK
U2 - 10.1029/2019JB018162
DO - 10.1029/2019JB018162
M3 - Article
AN - SCOPUS:85082333044
SN - 2169-9313
VL - 125
JO - Journal of Geophysical Research: Solid Earth
JF - Journal of Geophysical Research: Solid Earth
IS - 3
M1 - e2019JB018162
ER -