Coseismic electric and magnetic signals observed during 2017 Jiuzhaigou Mw 6.5 earthquake and explained by electrokinetics and magnetometer rotation

SUMMARY Very clear coseismic electric and magnetic signals accompanying seismic waves were observed during the 2017 Mw 6.5 Jiuzhaigou earthquake, which took place in western China. In order to understand the generation mechanism of these observed signals, we simulate electric and magnetic responses to this specific earthquake based on three mechanisms, namely, the electrokinetic effect, the motional induction effect and the rotation effect of the coil-type magnetometer. We conduct the simulations using a point source model and a realistic layered earth model and compare to the observed data in the frequency band 0.05–0.3 Hz. Our results show that the electrokinetic effect can explain the observed electric fields in both waveform and amplitude, but it cannot explain the magnetic signals accompanying the Rayleigh wave. The motional induction effect cannot explain either the coseismic electric or magnetic data because it predicts much weaker coseismic electric and magnetic fields than the observed data. The magnetic fields resulting from the rotation of the magnetometer agree with the observed data in the waveforms though their amplitudes are two to four times smaller than the observed data. Our simulations suggest that the electrokinetic effect is responsible for the generation of coseismic electric fields and that rotation of the coil magnetometer is likely the main cause of coseismic magnetic fields. The results improve our interpretation of the coseismic electromagnetic (EM) phenomenon and are useful for understanding other kinds of earthquake-associated EM phenomena.

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Semi-analytical solutions of seismo-electromagnetic signals arising from the motional induction in 3-D multi-layered media: part II—numerical investigations

Earth Planets and Space ◽

10.1186/s40623-021-01458-5 ◽

2021 ◽

Vol 73 (1) ◽

Author(s):

Hengxin Ren ◽

Ling Zeng ◽

Yao-Chong Sun ◽

Ken’ichi Yamazaki ◽

Qinghua Huang ◽

...

Keyword(s):

Point Source ◽

Numerical Computation ◽

Wave Velocity ◽

Excellent Agreement ◽

Seismic Waves ◽

Averaging Method ◽

Ground Surface ◽

Induction Effect ◽

Motional Induction ◽

Electromagnetic Signals

AbstractIn this paper, numerical computations are carried out to investigate the seismo-electromagnetic signals arising from the motional induction effect due to an earthquake source embedded in 3-D multi-layered media. First, our numerical computation approach that combines discrete wavenumber method, peak-trough averaging method, and point source stacking method is introduced in detail. The peak-trough averaging method helps overcome the slow convergence problem, which occurs when the source–receiver depth difference is small, allowing us to consider any focus depth. The point source stacking method is used to deal with a finite fault. Later, an excellent agreement between our method and the curvilinear grid finite-difference method for the seismic wave solutions is found, which to a certain degree verifies the validity of our method. Thereafter, numerical computation results of an air–solid two-layer model show that both a receiver below and another one above the ground surface will record electromagnetic (EM) signals showing up at the same time as seismic waves, that is, the so-called coseismic EM signals. These results suggest that the in-air coseismic magnetic signals reported previously, which were recorded by induction coils hung on trees, can be explained by the motional induction effect or maybe other seismo-electromagnetic coupling mechanisms. Further investigations of wave-field snapshots and theoretical analysis suggest that the seismic-to-EM conversion caused by the motional induction effect will give birth to evanescent EM waves when seismic waves arrive at an interface with an incident angle greater than the critical angle θc = arcsin(Vsei/Vem), where Vsei and Vem are seismic wave velocity and EM wave velocity, respectively. The computed EM signals in air are found to have an excellent agreement with the theoretically predicted amplitude decay characteristic for a single frequency and single wavenumber. The evanescent EM waves originating from a subsurface interface of conductivity contrast will contribute to the coseismic EM signals. Thus, the conductivity at depth will affect the coseismic EM signals recorded nearby the ground surface. Finally, a fault rupture spreading to the ground surface, an unexamined case in previous numerical computations of seismo-electromagnetic signals, is considered. The computation results once again indicate the motional induction effect can contribute to the coseismic EM signals.

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Calculation of Internal Electric Fields Induced in Each Body Part of Human Models by ELF and Intermediate Frequency Uniform Magnetic Fields

IEEJ Transactions on Fundamentals and Materials ◽

10.1541/ieejfms.140.580 ◽

2020 ◽

Vol 140 (12) ◽

pp. 580-585

Author(s):

Yoichi Sekiba ◽

Kenichi Yamazaki

Keyword(s):

Magnetic Fields ◽

Electric Fields ◽

Body Part ◽

Intermediate Frequency ◽

Human Models

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Millimeter (MM) wave and microwave frequency radiation produce deeply penetrating effects: the biology and the physics

Reviews on Environmental Health ◽

10.1515/reveh-2020-0165 ◽

2021 ◽

Vol 0 (0) ◽

Author(s):

Martin L. Pall

Keyword(s):

Magnetic Fields ◽

Electric Fields ◽

Cardiac Activity ◽

Maximum Level ◽

Voltage Sensor ◽

The Body ◽

Time Varying ◽

The Brain ◽

Mm Waves

Abstract Millimeter wave (MM-wave) electromagnetic fields (EMFs) are predicted to not produce penetrating effects in the body. The electric but not magnetic part of MM-EMFs are almost completely absorbed within the outer 1 mm of the body. Rodents are reported to have penetrating MM-wave impacts on the brain, the myocardium, liver, kidney and bone marrow. MM-waves produce electromagnetic sensitivity-like changes in rodent, frog and skate tissues. In humans, MM-waves have penetrating effects including impacts on the brain, producing EEG changes and other neurological/neuropsychiatric changes, increases in apparent electromagnetic hypersensitivity and produce changes on ulcers and cardiac activity. This review focuses on several issues required to understand penetrating effects of MM-waves and microwaves: 1. Electronically generated EMFs are coherent, producing much higher electrical and magnetic forces then do natural incoherent EMFs. 2. The fixed relationship between electrical and magnetic fields found in EMFs in a vacuum or highly permeable medium such as air, predicted by Maxwell’s equations, breaks down in other materials. Specifically, MM-wave electrical fields are almost completely absorbed in the outer 1 mm of the body due to the high dielectric constant of biological aqueous phases. However, the magnetic fields are very highly penetrating. 3. Time-varying magnetic fields have central roles in producing highly penetrating effects. The primary mechanism of EMF action is voltage-gated calcium channel (VGCC) activation with the EMFs acting via their forces on the voltage sensor, rather than by depolarization of the plasma membrane. Two distinct mechanisms, an indirect and a direct mechanism, are consistent with and predicted by the physics, to explain penetrating MM-wave VGCC activation via the voltage sensor. Time-varying coherent magnetic fields, as predicted by the Maxwell–Faraday version of Faraday’s law of induction, can put forces on ions dissolved in aqueous phases deep within the body, regenerating coherent electric fields which activate the VGCC voltage sensor. In addition, time-varying magnetic fields can directly put forces on the 20 charges in the VGCC voltage sensor. There are three very important findings here which are rarely recognized in the EMF scientific literature: coherence of electronically generated EMFs; the key role of time-varying magnetic fields in generating highly penetrating effects; the key role of both modulating and pure EMF pulses in greatly increasing very short term high level time-variation of magnetic and electric fields. It is probable that genuine safety guidelines must keep nanosecond timescale-variation of coherent electric and magnetic fields below some maximum level in order to produce genuine safety. These findings have important implications with regard to 5G radiation.

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Quark pair creation in color electric fields and effects of magnetic fields

Annals of Physics ◽

10.1016/j.aop.2010.03.012 ◽

2010 ◽

Vol 325 (9) ◽

pp. 2018-2040 ◽

Cited By ~ 20

Author(s):

Noato Tanji

Keyword(s):

Magnetic Fields ◽

Electric Fields ◽

Pair Creation

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A Case for Magneto Hydro Dynamics (MHD)

10.1115/imece2001/mems-23884 ◽

2001 ◽

Author(s):

Haim H. Bau

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Magnetic Flux ◽

Lorentz Force ◽

Electric Fields ◽

Biological Fluids ◽

Fluid Volume ◽

Chaotic Advection ◽

Complex Flows ◽

Electric Currents

Abstract In this paper, I review some of our work on the use of magneto hydrodynamics (MHD) for pumping, controlling, and stirring fluids in microdevices. In many applications, one operates with liquids that are at least slightly conductive such as biological fluids. By patterning electrodes inside flow conduits and subjecting these electrodes to potential differences, one can induce electric currents in the liquid. In the presence of a magnetic field, a Lorentz force is generated in a direction that is perpendicular to both the magnetic and electric fields. Since one has a great amount of freedom in patterning the electrodes, one can induce forces in various directions so as to generate complex flows including “guided” flows in virtual, wall-less channels. The magnetic flux generators can be either embedded in the device or be external. Despite their unfavorable scaling (the magnitude of the forces is proportional to the fluid volume), MHD offers many advantages such as the flexibility of applying forces in any desired direction and the ability to adjust the magnitude of the forces by adjusting either the electric and/or magnetic fields. We provide examples of (i) MHD pumps; (ii) controlled networks of conduits in which each conduit is equipped with a MHD actuator and by controlling the voltage applied to each actuator, one can direct the liquid to flow in any desired way without a need for valves; and (iii) MHD stirrers including stirrers that exhibit chaotic advection.

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