scholarly journals Electric and Electromagnetic Signals Under, on, and Above the Ground Surface at the Arrival of Seismic Waves

10.5772/27619 ◽  
2012 ◽  
Author(s):  
Akihiro Takeuchi ◽  
Kan Okubo ◽  
Nobunao Takeuchi
Keyword(s):  
Seismic Waves ◽  
Ground Surface ◽  
Electromagnetic Signals

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

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.

scholarly journals An analytical expression for early electromagnetic signals generated by impulsive line-currents in conductive Earth crust, with numerical examples

2016 ◽  
Vol 59 (2) ◽  
Author(s):  
Ken'ichi Yamazaki
Keyword(s):  
Seismic Waves ◽  
Ground Surface ◽  
Space Model ◽  
Whole Space ◽  
Source Current ◽  
Em Field ◽  
Electromagnetic Signals ◽  
Analytical Expressions ◽  
The Magnetic Field ◽  
Ground Conductivity

<p>Changes in the electromagnetic (EM) field after an earthquake rupture but before the arrival of seismic waves (“early EM signals”) have sometimes been reported. Quantitative evaluations are necessary to clarify whether the observed phenomena are accounted for by known theories and to assess whether the phenomenon can be applied to earthquake early warning. Therefore, analytical expressions for the magnetic field generated by an impulsive line-current are derived for a conductive half-space model, and for a two-layer model; the somewhat simpler situation of a conductive whole-space is also considered. By analyzing the expressions obtained for the generated EM field, some expected features of the early EM signals are discussed. First, I verify that an early EM signal arrives before the seismic waves unless conductivity is relatively high. Second, I show that early EM signals are well approximated by the whole-space model when the source is near the ground surface, but not when it is at depth. Third, I show that the expected amplitudes of early EM signals are within the detection limits of commonly used EM sensors, provided that ground conductivity is not very high and that the source current is sufficiently intense. However, this does not mean that the EM signals are easily distinguishable, because detector sensitivity does not account for additive noise or false positive detections.</p>

VERTICAL VELOCITIES FROM REFLECTION SHOOTING

Geophysics ◽  
1947 ◽  
Vol 12 (2) ◽  
pp. 221-228 ◽  
Author(s):  
L. W. Gardner
Keyword(s):  
Vertical Velocity ◽  
Seismic Waves ◽  
Ground Surface ◽  
Comparison Of Results ◽  
Favorable Conditions

Reflection seismograph observations supply a means of determining the average vertical velocity of seismic waves from the ground surface to the depth of any good reflecting horizon, through measurements of “angularity corrections.” Specially grouped arrangements of shot points and detectors are illustrated and described, which minimize error in making these measurements. Reflection seismograph observations using these arrangements were made at four locations where well velocity surveys were available. Comparison of results indicates that average vertical velocities good to within 3% can be obtained by this method, under favorable conditions.

scholarly journals Seismic Ground Response Analysis Based on Multilayer Perceptron and Convolution Neural Networks

2021 ◽  
Vol 21 (1) ◽  
pp. 231-238
Author(s):  
Seokgyeong Hong ◽  
Jaehun Ahn
Keyword(s):  
Neural Networks ◽  
Seismic Response ◽  
Multilayer Perceptron ◽  
Seismic Waves ◽  
Ground Surface ◽  
Average Error ◽  
Response Analysis ◽  
Ground Response Analysis ◽  
Analysis Process ◽  
Specific Frequency

The importance of establishing a disaster prevention plan considering seismic performance is being highlighted to reduce damage to structures caused by earthquakes. Earthquake waves propagate from the bedrock to the ground surface through the soil. During the transmission process, they are amplified in a specific frequency range, and the degree of amplification depends mainly on the characteristics of the ground. Therefore, a seismic response analysis process is essential for enhancing the reliability of the seismic design. We propose a model for predicting seismic waves on the surface from seismic waves measured on the bedrock based on Multilayer Perceptron (MLP) and Convolutional Neural Networks (CNN) and validate the applicability of the proposed model with Spectral Acceleration (SA). Both the proposed models based on MLP and CNN successfully predicted the seismic response of the surface. The CNN-based model performed better than the MLP-based model, with a 10% smaller average error. We plan to implement the physical properties of the ground, such as shear wave velocity, to create a more versatile model in the future.

Propagation Characteristics of Seismic Waves Taking Stratigraphic Composition into Consideration

2014 ◽  
Vol 989-994 ◽  
pp. 484-489
Author(s):  
Bin Bin Xu ◽  
Kentaro Nakai ◽  
Toshihiro Noda
Keyword(s):  
Seismic Waves ◽  
Ground Surface ◽  
Propagation Characteristics ◽  
Dense Sand ◽  
Sandy Ground ◽  
Acceleration Amplitude ◽  
Dynamic Analyses ◽  
Input Acceleration ◽  
Propagation Properties ◽  
Cam Clay

In this paper, soil-water coupled dynamic analyses are carried out to investigate the influence of stratigraphic composition on the propagation properties of the seismic waves. SYS Cam-clay model is used as the constitutive model which can describe the different state of clayey and sandy soils. Two cases are considered for the composition of ground: one is the sandy ground with diluvial sand, alluvial sand and reclaimed sand; the other one is the clayey layer at the ground surface. It is found that for the sandy ground even though there is certain amplification of the input acceleration wave during the dense sand layer the subsequent seismic waves through the loose sand layers are attenuated significantly due to the occurrence of the liquefaction. While for the clayey ground, even though there is no risk of liquefaction damages at the ground surface the acceleration amplitude is greatly amplified and there is a risk that the structure itself would fail in the strength.

Numerical Simulations of Canyon Topography Effects on Long-Span Bridge with High Piers under Incident SH Seismic Waves

2011 ◽  
Vol 378-379 ◽  
pp. 789-794
Author(s):  
Guo Liang Zhou ◽  
Xiao Jun Li ◽  
Qing Li Meng
Keyword(s):  
Oblique Incidence ◽  
Seismic Waves ◽  
Seismic Analysis ◽  
Ground Motions ◽  
Ground Surface ◽  
Analysis And Design ◽  
Long Span ◽  
Rigid Frame ◽  
Long Span Bridge ◽  
Canyon Topography

To evaluate the influences of the canyon topography on large structures, based on a rigid frame bridge across a 137-meter-deep and 600-meter-wide canyon, the seismic response of the canyon topography is analyzed under seismic SH waves with the assumptions of vertical incidence and oblique incidence to obtain the surface ground motions, which are used as the excitations for the bridge. It indicates that canyon topography has significant and complex influences on the surface ground motions. The peak ground accelerations vary greatly from the bottom of the canyon to the upper corners. And the ground surface has been characterized by larger relative displacements in the case of oblique incidence. Compared with the uniform seismic excitations, it’s hard to find out any regularity on structural seismic responses considering the canyon topography effects. The canyon topography can enlarge or minish the structural responses in terms of the different structure members, and it should be a carefully considered factor in structural seismic analysis and design.

scholarly journals Electric Signals on and under the Ground Surface Induced by Seismic Waves

2012 ◽  
Vol 2012 ◽  
pp. 1-10 ◽  
Author(s):  
Akihiro Takeuchi ◽  
Kan Okubo ◽  
Nobunao Takeuchi
Keyword(s):  
Seismic Waves ◽  
Streaming Potential ◽  
Ground Surface ◽  
Generation Model ◽  
Plate Electrode ◽  
Large Plate ◽  
Saturated Water ◽  
Water Zone ◽  
Northeastern Japan ◽  
Electric Signals

We constructed three observation sites in northeastern Japan (Honjo, Kyowa, and Sennan) with condenser-type large plate electrodes (4 × 4 m2) as sensors supported 4 m above the ground and with pairs of reference electrodes buried vertically at 0.5 m and 2.5 m depth (with a ground velocity sensor at Sennan only). Electrical signals of an earthquake (M6.3) in northeastern Japan were detected simultaneously with seismic waves. Their waveforms were damped oscillations, with greatly differing signal amplitudes among sites. Good positive correlation was found between the amplitudes of signals detected by all electrodes. We propose a signal generation model: seismic acceleration vertically shook pore water in the topsoil, generating the vertical streaming potential between the upper unsaturated water zone and the lower saturated water zone. Maximum electric earth potential difference was observed when one electrode was in the saturated water zone, and the other was within the unsaturated water zone, but not when the electrodes were in the saturated water zone. The streaming potential formed a charge on the ground surface, generating a vertical atmospheric electric field. The large plate electrode detected electric signals related to electric potential differences between the electrode and the ground surface.

SEISMIC WAVES FROM A TRANSDUCER AT THE SURFACE OF STRATIFIED GROUND

Geophysics ◽  
1956 ◽  
Vol 21 (4) ◽  
pp. 939-959 ◽  
Author(s):  
F. F. Evison
Keyword(s):  
Surface Layer ◽  
Rayleigh Wave ◽  
Rayleigh Waves ◽  
Seismic Waves ◽  
Ground Surface ◽  
Shear Velocity ◽  
Critical Distance ◽  
Variable Frequency ◽  
Independent Estimate ◽  
Refracted Waves

Vibration impulses of variable frequency and duration have been generated by means of an electrically excited vibrator and the resulting seismic waves recorded at the ground surface along a 200‐ft traverse. The first arrivals were refractions from the water table and a deeper clay‐siltstone interface, and these checked with the results of a standard refraction survey. The amplitudes of displacement of the refracted waves varied in each case with approximately the inverse square of distance; the critical distance was marked by a discontinuity of amplitude. Two later impulsive arrivals recorded within 50 msec of the first were interpreted respectively as a transformed reflection from 85 ft depth and an ordinary compressional reflection from 200 ft depth. A dispersive Rayleigh wave gave an independent estimate of the shear velocity and thickness of the surface layer. Air‐coupled waves of frequencies 70.8 cps and 330 cps were recorded and have been related to the first‐ and third‐mode Rayleigh waves respectively.

Piezoelectricity as a mechanism on generation of electromagnetic precursors before earthquakes

2020 ◽  
Vol 224 (1) ◽  
pp. 682-700
Author(s):  
Jeen-Hwa Wang
Keyword(s):  
Electric Field ◽  
Normal Stress ◽  
Ground Surface ◽  
Strike Slip ◽  
Normal Faults ◽  
Shear Stresses ◽  
Major Mechanism ◽  
Electromagnetic Signals ◽  
Fault Gouges ◽  
As Stress

SUMMARY To produce the electromagnetic (E&M) precursors of an earthquake, the existence of electric field due to stress-induced charges on the ground surface or in shallow depths of upper crust inside the fault zone is a basic condition. Here, we consider the piezoelectric effect or the elastic–electric coupling as a major mechanism on generating such an electric field. A 1-D model based on the elastic mechanics and electromagnetic Maxwell equations is built up to formulate the relationship between electric field and slip as well as stress on a fault before an earthquake. From the model, we may estimate the low-bound values of stress and slip to yield the critical electric field, Ec, for generation of electromagnetic signals. The normal and shear stresses on the fault planes for three faulting types are constructed. The normal stress is stronger than the shear stress to result in piezoelectricity. The depth ranges for yielding an average normal stress being able to generate Ec are similar for thrust and strike-slip faults and deep for normal faults. The possibility of generating Ec is almost the same for thrust and strike-slip faults and low for normal faults. The pre-earthquake slip could be related to nucleation phases or microfractures. The possible occurrence time of E&M signals may be several 10 min to few hours before impending earthquakes. The major factor in yielding a piezoelectric field to generate the TEC anomalies before an earthquake is the existence of fault gouges composed mainly of clays. A thick gouge layer with low electric resistivity and a piezoelectric coupling coefficient ≥0.67 × 10−12 coul  nt–1 is an important condition for yielding piezoelectricity.

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