MTS studies on the upper mantle conductivity in China

1987 ◽  
Vol 125 (2-3) ◽  
pp. 465-482 ◽  
Author(s):  
Liu Guodong
Keyword(s):  
Upper Mantle ◽  
Mantle Conductivity

Inversion of the satellite observations of the tidally induced magnetic field in terms of 3-D upper-mantle electrical conductivity: Method and synthetic tests

2021 ◽  
Author(s):  
Libor Šachl ◽  
Jakub Velímský ◽  
Javier Fullea
Keyword(s):  
Magnetic Field ◽  
Electrical Conductivity ◽  
Upper Mantle ◽  
Spherical Harmonic ◽  
Model Space ◽  
Conductivity Method ◽  
Satellite Gravity ◽  
Compositional Model ◽  
Mantle Conductivity ◽  
The Impact

<p><span><span>We have developed and tested a new frequency-domain, spherical harmonic-finite element approach to the inverse problem of global electromagnetic (EM) induction. It is based on the quasi-Newton minimization of data misfit and regularization, and uses the adjoint approach for fast calculation of misfit gradients in the model space. Thus, it allows for an effective inversion of satellite-observed magnetic field induced by tidally driven flows in the Earth's oceans in terms of 3-D structure of the electrical conductivity in the upper mantle.</span></span><span><span> Before proceeding to the inversion of Swarm-derived models of tidal magnetic signatures, we have performed a series of </span></span><span><span>parametric studies</span></span><span><span>, using a 3-D conductivity model WINTERC-e as a testbed.</span></span></p><p><span>The WINTERC-e model has been derived using state-of-the-art laboratory conductivity measurements of mantle minerals, and thermal and compositional model of the lithosphere and upper mantle WINTERC-grav. The latter model is based on the inversion of global surface waveforms, satellite gravity and gradiometry measurements, surface elevation, and heat flow data </span><span><span>in a thermodynamically self-consistent framework. </span></span><span><span>Therefore, the WINTERC-e model, independent of any EM data, represents an ideal target for synthetic tests of the 3-D EM inversion.</span></span><span> </span></p><p><span><span>We tested the impact of </span></span><span><span>the </span></span><span><span>satellite </span></span><span><span>altitude</span></span><span><span>, </span></span><span><span>the truncation degree of the </span></span><span><span>spherical-harmonic </span></span><span><span>expansion of the tidal signals, the random</span></span><span><span> noise in data</span></span><span><span>,</span></span><span> </span><span><span>and </span></span><span><span>of the </span></span><span><span>sub-</span></span><span><span>continental conductivity</span></span><span> </span><span><span>on the </span></span><span><span>ability to recover the sub-oceanic upper-mantle conductivity structure.</span></span><span><span> We </span></span><span><span>demonstrate </span></span><span><span>that </span></span><span><span>with </span></span><span><span>suitable regularization </span></span><span><span>we</span></span><span> </span><span><span>can successfully reconstruct the 3D upper-mantle conductivity below world oceans.</span></span></p>

scholarly journals Upper mantle conductivity structure of the back-arc region beneath northeastern China

2001 ◽  
Vol 28 (19) ◽  
pp. 3773-3776 ◽  
Author(s):  
Masahiro Ichiki ◽  
Makoto Uyeshima ◽  
Hisashi Utada ◽  
Zhao Guoze ◽  
Tang Ji ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Northeastern China ◽  
Conductivity Structure ◽  
Mantle Conductivity ◽  
Back Arc

A review of electromagnetic investigations in the Kapuskasing uplift and surrounding regions: electrical properties of key rocks

1994 ◽  
Vol 31 (7) ◽  
pp. 1042-1051 ◽  
Author(s):  
Marianne Mareschal ◽  
Ron D. Kurtz ◽  
Richard C. Bailey
Keyword(s):  
Grain Boundaries ◽  
Upper Mantle ◽  
Field Measurements ◽  
Surface Expression ◽  
High Grade ◽  
Near Surface ◽  
Solid Films ◽  
Conductivity Structure ◽  
Mantle Conductivity ◽  
Detachment Zone

Electromagnetic investigations of the Kapuskasing uplift show that the gross electrical conductivity structure of the present crust is subhorizontal (contrary to the lithology as defined by seismic experiments), with increasing conductivity with depth, a feature common to most continental crusts. The current upper crust of the Chapleau block includes zones of reduced resistivity; the near-surface expression of the Ivanhoe Lake cataclastic zone (< 1 km in depth and 600 m in width), with resistivities of a few hundred ohm metres, is typical of fluid infilling weathered rocks. At least two other zones are less resistive (ρ < 12 kΩ∙m) than the typical upper-crustal Chapleau block (> 40 kΩ∙m), these include a subhorizontal layer at ~ 5 km and a subhorizontal to dipping layer at ~ 2 km. The deeper layer is interpreted as imaging deep fluids (porosities > 0.5%) postdating the uplift. The shallower feature, possibly related to the seismically detected detachment zone dipping at ~ 15° could be imaging conductors such as recent fluids or remnants of solid films precipitated at grain boundaries by more ancient fluids.Auger spectrometry of high-grade rocks exposed near the extrapolated surface expression of the shallower conductor reveals that fragments of graphite films (3–30 nm thick) are commonly found at grain boundaries, whereas traces of sulphur and chlorine are relatively rare. The electrical resistivity of these rocks was measured in laboratory and is lower than normally observed for similar high-grade rocks from other parts of the Canadian shield (5–25 kΩ∙m as opposed to 30–100 kΩ∙m).The Kapuskasing Uplift has opened a new area of research on upper-mantle conductivity structure from surface electromagnetic field measurements, an endeavour believed impossible until now.

Sea Bottom EM Field of M2 Tidal to Probe Upper Mantle Conductivity

2013 ◽  
Vol 683 ◽  
pp. 828-831
Author(s):  
Yan Xu ◽  
Jun Xu ◽  
Wen Hu Zhang
Keyword(s):  
Upper Mantle ◽  
Period Range ◽  
Partial Melt ◽  
The Earth ◽  
Ionospheric Source ◽  
Sea Bottom ◽  
Mantle Conductivity ◽  
Em Field ◽  
Recent Laboratory

Recent laboratory experiments demonstrate that electrical conductivity of upper mantle (UM) minerals is greatly increased by small amounts of water or by partial melt. Determination of deep conductivity using electromagnetic (EM) methods can thus provide constraints on the presence of volatiles and melting processes in UM. Probing conductivity at UM depths requires EM data with periods of a few to one cycle per day. This is a challenging period range for EM studies due to the spatially complex ionospheric source that dominates at these periods. The idea of exploiting tidal signals for EM studies of the Earth is not new, but so far it was used only for interpretation of inland and transoceanic electric field data due to M2. Emphasis in this work is made on a discussion of sea bottom magnetic field of the same origin.

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