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<p>Long-running geomagnetic observatories accumulate abundant data to probe Earth’s mantle conductivity and constrain mantle hydration, temperature, and partial melting. We analyze time series of 163 mid-latitude geomagnetic observatories from 1997 to 2021. The Sq source is built using a spherical harmonic (SH) term set with horizontal magnetic fields at frequencies of 1–6 cpd (cycle per day). Once SH coefficients on magnetically quiet equinoctial days are obtained, transfer functions (TFs) with the radial magnetic field are estimated. The linear equation system is solved with the iterative reweighted least-squares (IRLS) regression. 1D mantle conductivity beneath Alice Springs observatory (code: ASP) and European ones is inverted using the L-BFGS algorithm, and real-time ground magnetic fields are subsequently calculated. Referring to the database on mantle mineral water content from Yoshino et al., we find that upper mantle conductivity beneath ASP and Kyiv observatory (code: KIV) is lower than the global average, and water content <i>C</i><sub><i>w</i></sub> in the mantle transition zone (MTZ) at ASP is approximately 0.1 wt.%. Upper mantle conductivity in central and eastern Europe with <i>C</i><sub><i>w</i></sub> &lt; 0.1 wt.% is lower than the surrounding horizontal values. Upper mantle and upper MTZ conductivity with <i>C</i><sub><i>w</i></sub> ∈ [0.1, 0.3] wt.% increase in southern Europe, and the increased water content suggests that the Mediterranean subducted slab is dehydrated before reaching the lower MTZ. As the depth increases, the lower MTZ conductivity lateral variation decreases, and water content increases to 1 wt.%.</p>

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Study on electrical conductivity of Europe’s upper mantle and transition zone using geomagnetic diurnal variations

  • 期刊论文

  • 发表日期：

    2026年5月19日

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  • Daolin Yang,
  • Shan Xu,
  • Chaojian Chen,
  • Xiangyun Hu

摘要

Long-running geomagnetic observatories accumulate abundant data to probe Earth’s mantle conductivity and constrain mantle hydration, temperature, and partial melting. We analyze time series of 163 mid-latitude geomagnetic observatories from 1997 to 2021. The Sq source is built using a spherical harmonic (SH) term set with horizontal magnetic fields at frequencies of 1–6 cpd (cycle per day). Once SH coefficients on magnetically quiet equinoctial days are obtained, transfer functions (TFs) with the radial magnetic field are estimated. The linear equation system is solved with the iterative reweighted least-squares (IRLS) regression. 1D mantle conductivity beneath Alice Springs observatory (code: ASP) and European ones is inverted using the L-BFGS algorithm, and real-time ground magnetic fields are subsequently calculated. Referring to the database on mantle mineral water content from Yoshino et al., we find that upper mantle conductivity beneath ASP and Kyiv observatory (code: KIV) is lower than the global average, and water content Cw in the mantle transition zone (MTZ) at ASP is approximately 0.1 wt.%. Upper mantle conductivity in central and eastern Europe with Cw < 0.1 wt.% is lower than the surrounding horizontal values. Upper mantle and upper MTZ conductivity with Cw ∈ [0.1, 0.3] wt.% increase in southern Europe, and the increased water content suggests that the Mediterranean subducted slab is dehydrated before reaching the lower MTZ. As the depth increases, the lower MTZ conductivity lateral variation decreases, and water content increases to 1 wt.%.