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    <title>Journal of Studies of Earth’s Deep Interior - Latest Publications</title>
    <description>Latest articles</description>
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    <pubDate>Sun, 05 Apr 2026 07:08:56 +0000</pubDate>
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    <author>Journal of Studies of Earth’s Deep Interior</author>
    <dc:creator>Journal of Studies of Earth’s Deep Interior</dc:creator>
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      <title>Constraints on the lower mantle electrical conductivity from length-of-day changes</title>
      <description><![CDATA[We investigate how the radial profile σ(r) of the lower mantle electrical conductivity affects the downward continuation of the time-varying magnetic field to the core surface and the resulting inverted core motions. We compare core flow predictions to the length-of-day (LOD) with geodetic records, in order to assess how plausible the considered conductivity profiles are. The core flow inverse problem, mixing the information carried by single spherical harmonic magnetic coefficients, makes it non trivial to infer the delay expected for LOD predictions. Our results indicate that the timescale characteristic of the mantle filter in the low-frequency limit yields an integral measure of σ(r) allowing us to select admissible conductivity models. Models of σ(r) inferred from magnetospheric and tidal sources over the satellite era involve mantle filter lags less than a couple of months and provide the best fit to LOD variations. Other conductivity profiles constructed based on mineralogical properties and iron partitioning inferred for deep mantle rocks (i.e., σ increasing from a few S/m at 1200 km depth up to some tens of S/m ~ 300 km above the core surface, with a more conducting D'' layer) are acceptable. A highly conducting layer of thickness O(10 km) or thinner cannot be excluded.]]></description>
      <pubDate>Thu, 06 Nov 2025 23:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jsedi.16005</link>
      <guid>https://doi.org/10.46298/jsedi.16005</guid>
      <author>Gillet, Nicolas</author>
      <author>Martinec, Zdenek</author>
      <author>Lepage, Thea</author>
      <author>Jault, Dominique</author>
      <dc:creator>Gillet, Nicolas</dc:creator>
      <dc:creator>Martinec, Zdenek</dc:creator>
      <dc:creator>Lepage, Thea</dc:creator>
      <dc:creator>Jault, Dominique</dc:creator>
      <content:encoded><![CDATA[We investigate how the radial profile σ(r) of the lower mantle electrical conductivity affects the downward continuation of the time-varying magnetic field to the core surface and the resulting inverted core motions. We compare core flow predictions to the length-of-day (LOD) with geodetic records, in order to assess how plausible the considered conductivity profiles are. The core flow inverse problem, mixing the information carried by single spherical harmonic magnetic coefficients, makes it non trivial to infer the delay expected for LOD predictions. Our results indicate that the timescale characteristic of the mantle filter in the low-frequency limit yields an integral measure of σ(r) allowing us to select admissible conductivity models. Models of σ(r) inferred from magnetospheric and tidal sources over the satellite era involve mantle filter lags less than a couple of months and provide the best fit to LOD variations. Other conductivity profiles constructed based on mineralogical properties and iron partitioning inferred for deep mantle rocks (i.e., σ increasing from a few S/m at 1200 km depth up to some tens of S/m ~ 300 km above the core surface, with a more conducting D'' layer) are acceptable. A highly conducting layer of thickness O(10 km) or thinner cannot be excluded.]]></content:encoded>
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      <title>Influence of background magnetic fields on the excitation of Magneto-Coriolis modes inside the Earth's core</title>
      <description><![CDATA[Magneto-Coriolis (QG-MC) waves are considered an important part of the rapid dynamics of the Earth's outer core.The detailed characteristics of these waves are however still under scrutiny.In this study we explore the sensitivity of the QG-MC waves to the background magnetic field over which they propagate and the frequency of a periodic perturbation that we impose.We retrieve QG-MC modes by analysing the velocity fields, where they are most easily observed.Concentrations of QG-MC waves in the magnetic field at the core surface in our model are reminiscent of recently observed geomagnetic jerks.The QG-MC waves are weakly sensitive to the details of the background magnetic field during their travel in the bulk and their frequency at the core surface remains close to that of the initial perturbation.This is a potential asset for the prediction of their evolution.Moreover, the waves in the system exhibit a complex relation with the initial perturbation: when the frequency of the initial pulsation is greater than a threshold -- depending on the Alfvén speed of the medium -- inward QG-Alfvén waves are recovered at the core mantle boundary instead of QG-MC waves, and we find that the waves evolve from QG-MC to QG-Alfvén waves depending on the input frequency.Thus, gradually increasing the input frequency in the system, we retrieve the dispersion relation for QG-MC waves with an evolution from a k_s^4 slope to a k_s^1 slope, where k_s is the cylindrical radial wavenumber, as waves transition from QG-MC to QG-Alfvén waves.We actually recover all the components of the dispersion relation from QG-MC waves at low pulsation \omega to QG-Alfvén and inertial waves at high pulsation \omega.Applying our results to the Earth's core, we expect to be able to recover QG-MC waves with confidence in the Earth core with periods between 57y and 2.8y.]]></description>
      <pubDate>Thu, 23 Oct 2025 20:27:58 +0000</pubDate>
      <link>https://doi.org/10.46298/jsedi.15652</link>
      <guid>https://doi.org/10.46298/jsedi.15652</guid>
      <author>Barrois, Olivier</author>
      <author>Aubert, Julien</author>
      <dc:creator>Barrois, Olivier</dc:creator>
      <dc:creator>Aubert, Julien</dc:creator>
      <content:encoded><![CDATA[Magneto-Coriolis (QG-MC) waves are considered an important part of the rapid dynamics of the Earth's outer core.The detailed characteristics of these waves are however still under scrutiny.In this study we explore the sensitivity of the QG-MC waves to the background magnetic field over which they propagate and the frequency of a periodic perturbation that we impose.We retrieve QG-MC modes by analysing the velocity fields, where they are most easily observed.Concentrations of QG-MC waves in the magnetic field at the core surface in our model are reminiscent of recently observed geomagnetic jerks.The QG-MC waves are weakly sensitive to the details of the background magnetic field during their travel in the bulk and their frequency at the core surface remains close to that of the initial perturbation.This is a potential asset for the prediction of their evolution.Moreover, the waves in the system exhibit a complex relation with the initial perturbation: when the frequency of the initial pulsation is greater than a threshold -- depending on the Alfvén speed of the medium -- inward QG-Alfvén waves are recovered at the core mantle boundary instead of QG-MC waves, and we find that the waves evolve from QG-MC to QG-Alfvén waves depending on the input frequency.Thus, gradually increasing the input frequency in the system, we retrieve the dispersion relation for QG-MC waves with an evolution from a k_s^4 slope to a k_s^1 slope, where k_s is the cylindrical radial wavenumber, as waves transition from QG-MC to QG-Alfvén waves.We actually recover all the components of the dispersion relation from QG-MC waves at low pulsation \omega to QG-Alfvén and inertial waves at high pulsation \omega.Applying our results to the Earth's core, we expect to be able to recover QG-MC waves with confidence in the Earth core with periods between 57y and 2.8y.]]></content:encoded>
      <slash:comments>0</slash:comments>
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      <title>Evidence of a ULVZ near Vanuatu from Sdiff postcursors</title>
      <description><![CDATA[Thin anomalous structures known as ultra-low velocity zones (ULVZs) have been found on the core-mantle boundary (CMB) and have extreme velocity reductions. These features are detected due to their effect on seismic waves that travel through them, typically producing precursors or postcursors. In this study we use postcursors to shear core-diffracted waves (Sdiff+) that sample the CMB near Vanuatu to detect and characterise the properties of a ULVZ. We identified a total of 19 earthquakes originating from the South Pacific Rise region detected by stations across East Asia — particularly Japan — showing Sdiff+ signals. Of these events, six with the highest quality Sdiff+ signals are included in a Bayesian inversion of travel times using the 2D Wavefront Tracker we previously developed. A subset of events was selected for further analysis by modelling using 3D full waveform synthetics for a range of parameters. The comparison of the real data with the synthetic waveforms suggests that a ULVZ is located to the southeast of Vanuatu at 172.2±0.9 °E and 22.9±1.1 °S and its broad-scale structure can be approximated as a cylinder with a height of 20±5 km, radius 240±50 km, and shear wave velocity reduction of 30±5%. These parameters are comparable to other ULVZs previously detected and modelled with Sdiff and Sdiff+. There are appreciable uncertainties in the location along the NW-SE direction due to the distribution of earthquakes and seismic arrays, as well as trade-offs between the height, size and velocity reduction of the ULVZ. Other studies using SPdKS, ScP and PcP have reported detections of ULVZs in the proximate region, some of which are consistent with the well-fitting parameter space of the ULVZ in this study. The Vanuatu ULVZ lies within the southwest edge of the Pacific large low velocity province. There is potentially a mantle plume rooted by this ULVZ that has diverted towards the hotspots on the eastern Australian plate around the Tonga slab, although most tomographic models do not show a continuous plume here. ]]></description>
      <pubDate>Thu, 16 Oct 2025 12:07:38 +0000</pubDate>
      <link>https://doi.org/10.46298/jsedi.15883</link>
      <guid>https://doi.org/10.46298/jsedi.15883</guid>
      <author>Martin, Carl</author>
      <author>Harmsma, Lobke</author>
      <author>Atkins, James</author>
      <author>Deuss, Arwen</author>
      <author>Cottaar, Sanne</author>
      <dc:creator>Martin, Carl</dc:creator>
      <dc:creator>Harmsma, Lobke</dc:creator>
      <dc:creator>Atkins, James</dc:creator>
      <dc:creator>Deuss, Arwen</dc:creator>
      <dc:creator>Cottaar, Sanne</dc:creator>
      <content:encoded><![CDATA[Thin anomalous structures known as ultra-low velocity zones (ULVZs) have been found on the core-mantle boundary (CMB) and have extreme velocity reductions. These features are detected due to their effect on seismic waves that travel through them, typically producing precursors or postcursors. In this study we use postcursors to shear core-diffracted waves (Sdiff+) that sample the CMB near Vanuatu to detect and characterise the properties of a ULVZ. We identified a total of 19 earthquakes originating from the South Pacific Rise region detected by stations across East Asia — particularly Japan — showing Sdiff+ signals. Of these events, six with the highest quality Sdiff+ signals are included in a Bayesian inversion of travel times using the 2D Wavefront Tracker we previously developed. A subset of events was selected for further analysis by modelling using 3D full waveform synthetics for a range of parameters. The comparison of the real data with the synthetic waveforms suggests that a ULVZ is located to the southeast of Vanuatu at 172.2±0.9 °E and 22.9±1.1 °S and its broad-scale structure can be approximated as a cylinder with a height of 20±5 km, radius 240±50 km, and shear wave velocity reduction of 30±5%. These parameters are comparable to other ULVZs previously detected and modelled with Sdiff and Sdiff+. There are appreciable uncertainties in the location along the NW-SE direction due to the distribution of earthquakes and seismic arrays, as well as trade-offs between the height, size and velocity reduction of the ULVZ. Other studies using SPdKS, ScP and PcP have reported detections of ULVZs in the proximate region, some of which are consistent with the well-fitting parameter space of the ULVZ in this study. The Vanuatu ULVZ lies within the southwest edge of the Pacific large low velocity province. There is potentially a mantle plume rooted by this ULVZ that has diverted towards the hotspots on the eastern Australian plate around the Tonga slab, although most tomographic models do not show a continuous plume here. ]]></content:encoded>
      <slash:comments>0</slash:comments>
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    <item>
      <title>The mantle-inner core gravitational mode of oscillation in a strong magnetic field regime</title>
      <description><![CDATA[The mantle-inner core gravitational (MICG) mode is the free mode axial oscillation between the mantle and inner core sustained by the gravitational torque between their degree 2 order 2 density structures. As part of this mode, the tangent cylinder (TC) is entrained to move jointly with the inner core, and the oscillations of the TC launch Alfvén waves propagating in the region outside the TC. Here, we investigate how the MICG is altered by the strength of the internal magnetic field in the core which controls the travelling speed of Alfvén waves. We show that the MICG mode remains a distinct normal mode of oscillation of the core-mantle system only when Alfvén waves are attenuated before they traverse the width of the fluid core. For an internal magnetic field strength of a few mT, as we expect in Earth's core, Alfvén waves can readily traverse the width of the core, and the MICG mode is absorbed into the spectrum of torsional oscillation (TO) modes. The MICG period retains a dynamical influence, acting as a point of resonance for TO modes, and marking the transition from a TO mode that is weakly impacted by gravitational coupling to one in which the motion of the TC (including the inner core) is strongly restricted. Our results imply that the observed 6-year periodic signal in the length of day cannot be interpreted as the signature of the MICG mode and must instead be caused by TO modes, or more generally, by the propagation of Alfvén waves.]]></description>
      <pubDate>Thu, 25 Sep 2025 22:00:00 +0000</pubDate>
      <link>https://doi.org/10.46298/jsedi.15735</link>
      <guid>https://doi.org/10.46298/jsedi.15735</guid>
      <author>Dumberry, Mathieu</author>
      <dc:creator>Dumberry, Mathieu</dc:creator>
      <content:encoded><![CDATA[The mantle-inner core gravitational (MICG) mode is the free mode axial oscillation between the mantle and inner core sustained by the gravitational torque between their degree 2 order 2 density structures. As part of this mode, the tangent cylinder (TC) is entrained to move jointly with the inner core, and the oscillations of the TC launch Alfvén waves propagating in the region outside the TC. Here, we investigate how the MICG is altered by the strength of the internal magnetic field in the core which controls the travelling speed of Alfvén waves. We show that the MICG mode remains a distinct normal mode of oscillation of the core-mantle system only when Alfvén waves are attenuated before they traverse the width of the fluid core. For an internal magnetic field strength of a few mT, as we expect in Earth's core, Alfvén waves can readily traverse the width of the core, and the MICG mode is absorbed into the spectrum of torsional oscillation (TO) modes. The MICG period retains a dynamical influence, acting as a point of resonance for TO modes, and marking the transition from a TO mode that is weakly impacted by gravitational coupling to one in which the motion of the TC (including the inner core) is strongly restricted. Our results imply that the observed 6-year periodic signal in the length of day cannot be interpreted as the signature of the MICG mode and must instead be caused by TO modes, or more generally, by the propagation of Alfvén waves.]]></content:encoded>
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