scholarly journals Indications of Ground-based Electromagnetic Observations to A Possible Lithosphere–Atmosphere–Ionosphere Electromagnetic Coupling before the 12 May 2008 Wenchuan MS 8.0 Earthquake

Atmosphere ◽  
2019 ◽  
Vol 10 (7) ◽  
pp. 355 ◽  
Author(s):  
Mei Li ◽  
Jun Lu ◽  
Xuemin Zhang ◽  
Xuhui Shen
Keyword(s):  
Electromagnetic Coupling ◽  
Conjugate Point ◽  
Low Frequency ◽  
Evolutionary Process ◽  
Ionospheric Disturbances ◽  
Electrical Field ◽  
Opposite Hemisphere ◽  
Epicentral Area ◽  
Electromagnetic Disturbances ◽  
Wenchuan Ms 8.0 Earthquake

A large number of various precursors have been reported since the Wenchuan MS 8.0 earthquake (EQ) took place on 12 May 2008 in China. In this work, previous investigations of both ground-based electromagnetic (EM) parameters and spatial ionospheric parameters were first examined. The statistical results showed that various anomalies presented different time-scale variations but tended to be characterized by a common feature – reaching their climax on 9 May, three days before the Wenchuan event, which indicates a lithosphere–atmosphere–ionosphere (LAI) electromagnetic coupling. Second, the fluctuations on 9 May based on the observational ground-based ultra low frequency (ULF) electrical field at the Gaobeidian (GBD) station and the direct current/ultra low frequency (DC–ULF) geomagnetic vertical Z field at the Chengdu (CD) station were comparably analyzed with those of ionospheric disturbances reported previously. The results showed that distinct electromagnetic changes, geomagnetic “double low-point” phenomena, and ionospheric disturbances above both sides of the Earth started in turn, respectively, but reached their climax simultaneously within dozens of hours on 9 May. This evolutionary process increases the probability that electromagnetic energy propagates from the epicentral area, via the atmosphere and ionosphere, to the equatorial plane, and through this plane finally to its magnetically conjugated area in the opposite hemisphere, causing electromagnetic disturbances on the Earth’s surface, in the atmosphere, and in the ionosphere and its conjugate point, in that order.

scholarly journals A study of atmospheric gravity waves and travelling ionospheric disturbances at equatorial latitudes

1997 ◽  
Vol 15 (8) ◽  
pp. 1048-1056 ◽  
Author(s):  
R. L. Balthazor ◽  
R. J. Moffett
Keyword(s):  
Gravity Waves ◽  
Large Scale ◽  
Ionospheric Disturbance ◽  
Magnetic Equator ◽  
Ionospheric Disturbances ◽  
Atmospheric Gravity Waves ◽  
Opposite Hemisphere ◽  
Travelling Ionospheric Disturbances ◽  
F Region ◽  
Atmospheric Gravity

Abstract. A global coupled thermosphere-ionosphere-plasmasphere model is used to simulate a family of large-scale imperfectly ducted atmospheric gravity waves (AGWs) and associated travelling ionospheric disturbances (TIDs) originating at conjugate magnetic latitudes in the north and south auroral zones and subsequently propagating meridionally to equatorial latitudes. A 'fast' dominant mode and two slower modes are identified. We find that, at the magnetic equator, all the clearly identified modes of AGW interfere constructively and pass through to the opposite hemisphere with unchanged velocity. At F-region altitudes the 'fast' AGW has the largest amplitude, and when northward propagating and southward propagating modes interfere at the equator, the TID (as parameterised by the fractional change in the electron density at the F2 peak) increases in magnitude at the equator. The amplitude of the TID at the magnetic equator is increased compared to mid-latitudes in both upper and lower F-regions with a larger increase in the upper F-region. The ionospheric disturbance at the equator persists in the upper F-region for about 1 hour and in the lower F-region for 2.5 hours after the AGWs first interfere, and it is suggested that this is due to enhancements of the TID by slower AGW modes arriving later at the magnetic equator. The complex effects of the interplays of the TIDs generated in the equatorial plasmasphere are analysed by examining neutral and ion winds predicted by the model, and are demonstrated to be consequences of the forcing of the plasmasphere along the magnetic field lines by the neutral air pressure wave.

Effects of Electrical Characters on Electrical Fatigue Behavior in PLZT Ferroelectric Ceramics

2007 ◽  
Vol 280-283 ◽  
pp. 159-162 ◽  
Author(s):  
Zhi Wu Chen ◽  
Zhen Ya Lu ◽  
Xu Ming Chen ◽  
Ying Zhang ◽  
Xuan Cheng
Keyword(s):  
Domain Switching ◽  
Fatigue Behavior ◽  
Low Frequency ◽  
Quantitative Information ◽  
Sine Wave ◽  
Sem Analysis ◽  
Fatigue Tests ◽  
Ferroelectric Ceramics ◽  
Electrical Field ◽  
Field Magnitude

Electrical fatigue tests have been conducted on PLZT ferroelectric ceramics. It was found that the higher the applied electrical field magnitude, the faster the Pr decreases; the samples under the same electrical field magnitude but with square wave have higher fatigue rate than that of sine wave. It was observed that at low frequency of applied field (50Hz and 500Hz), the polarization decreased very quickly and dropped below 70% of the original value within 106.2 switching cycles, however, when fatigue test were conducted at high frequencies of 100kHz and 300kHz, the polarization did not change significantly even after 109 cycles. The SEM analysis indicated that the facture mode was mainly of trans-granular for the virgin non-fatigued sample, while of inter-granular for the fatigue sample. The quantitative information on the 90° domain switching was measured in situ using X-ray diffraction. The effects of electrical characters on electrical fatigue behavior were explained according to the mechanism of electrical fatigue in PLZT ferroelectric ceramics.

Low-frequency rhythms in the thalamus of intact-cortex and decorticated cats

1996 ◽  
Vol 76 (6) ◽  
pp. 4152-4168 ◽  
Author(s):  
I. Timofeev ◽  
M. Steriade
Keyword(s):  
Right Hemisphere ◽  
Low Frequency ◽  
Slow Oscillation ◽  
Intracellular Recordings ◽  
Thalamic Nuclei ◽  
Opposite Hemisphere ◽  
Close Time ◽  
Intact Cortex ◽  
Corticothalamic Feedback ◽  
Delta Oscillation

1. The patterns and synchronization of low-frequency, sleeplike rhythms (slow, spindle and delta oscillations) were compared in the intact-cortex and decorticated hemispheres of cats under ketamine-xylazine anesthesia. Intracellular recordings were performed in intact and decorticated hemispheres from 58 rostrolateral thalamic reticular (RE) neurons and from 164 thalamocortical (TC) neurons in the ventrolateral (VL) nucleus. In the decorticated hemisphere, dual intracellular recordings were performed from five RE-VL cell couples and from 12 TC cell couples within the VL nucleus. In addition, field potentials were simultaneously recorded from the neocortex (electroencephalogram) and ipsilateral thalamus [electrothalamogram (EThG)] of the intact (right) hemisphere, while EThG was recorded from the VL nucleus of the decorticated (left) hemisphere. 2. The slow oscillation (< 1 Hz) was absent in all 72 VL cells and in 23 of 25 RE cells from the decorticated hemisphere, as well as in the EThG recorded from the VL nucleus in the decorticated hemisphere, whereas it was simultaneously present in the cortex and thalamus of the intact hemisphere. The remaining two RE neurons (8%) in the decorticated hemisphere oscillated in close time relation with the slow oscillation in the cortex and thalamus of the opposite hemisphere; averaged activities showed that the onset of depolarization in RE cell followed 12 ms after the sharp depth-negative (depolarizing) component in the contralateral cortex. We view this result as the electrophysiological correlate of a disynaptic excitatory pathway consisting of crossed cortical projections, first relayed in contralateral dorsal thalamic nuclei. 3. The patterns of thalamic spindles (7–14 Hz) differed between the two hemispheres. Whereas the decorticated hemisphere displayed prolonged, waxing and waning spindles, the spindles in the intact-cortex hemisphere were short and exclusively waning and followed the depth-negative component of cortical slow oscillation. This result indicates that the synchronized corticothalamic drive associated with the slow oscillation fully entrains thalamic circuits from the onset of spindles, thus preventing further waxing. Similar differences between waxing and waning and waning spindles were obtained by stimulating with different intensities the thalamus in the decorticated hemisphere. 4. Simultaneous intracellular recordings from two VL cells or from RE and VL cells showed nearly simultaneous spindle sequences in the decorticated hemisphere. 5. The hyperpolarization-activated intrinsic delta oscillation (1–4 Hz) of TC cells was asynchronous in the decorticated hemisphere. 6. These results strengthen the idea that the slow oscillation is cortical in origin; demonstrate a full, short-range, intrathalamic synchrony of spindles in the absence of cortex; and indicate that the pattern of spindles, a sleep rhythm that is conventionally regarded as purely thalamic, is shaped by the corticothalamic feedback.

scholarly journals Selective strolls: fixation and extinction in diploids are slower for weakly selected mutations than for neutral ones

2015 ◽  
Author(s):  
fabrizio mafessoni ◽  
Michael Lachmann
Keyword(s):  
Genetic Diversity ◽  
Natural Selection ◽  
Low Frequency ◽  
Evolutionary Process ◽  
Deleterious Mutations ◽  
Finite Populations ◽  
Slightly Deleterious Mutations ◽  
Getting Lost ◽  
Genetic Signatures ◽  
Diploid Populations

In finite populations, an allele disappears or reaches fixation due to two main forces, selection and drift. Selection is generally thought to accelerate the process: a selected mutation will reach fixation faster than a neutral one, and a disadvantageous one will quickly disappear from the population. We show that even in simple diploid populations, this is often not true. Dominance and recessivity unexpectedly slow down the evolutionary process for weakly selected alleles. In particular, slightly advantageous dominant and mildly deleterious recessive mu- tations reach fixation more slowly than neutral ones. This phenomenon determines genetic signatures opposite to those expected under strong selection, such as increased instead of decreased genetic diversity around the selected site. Furthermore, we characterize a new phenomenon: mildly deleterious recessive alleles, thought to represent the vast majority of newly arising mutations, survive in a population longer than neutral ones, before getting lost. Hence, natural selection is less effective than previously thought in getting rid rapidly of slightly negative mutations, contributing their observed persistence in present populations. Consequently, low frequency slightly deleterious mutations are on average older than neutral ones.

Seismic shaking scenarios for city of Zagreb, Croatia

2021 ◽  
Author(s):  
Helena Latečki ◽  
Josip Stipčević ◽  
Irene Molinari
Keyword(s):  
Goodness Of Fit ◽  
Synthetic Data ◽  
Low Frequency ◽  
Peak Ground Velocity ◽  
Hybrid Technique ◽  
Epicentral Area ◽  
Area Of Interest ◽  
Dense Grid ◽  
Broadband Seismograms ◽  
Zagreb Area

&lt;p&gt;In order to assess the seismic shaking levels, following the strong Zagreb March 22nd 2020 earthquake, we compute broadband seismograms using a hybrid technique. In a hybrid technique, low frequency (LF, f &lt; 1 Hz) and high frequency (HF, f = 1&amp;#8211;10 Hz) seismograms are obtained separately and then merged into a single time series. The LF part of seismogram is computed using a deterministic approach while for the HF part, we adopt the semi-stochastic method following the work of Graves and Pitarka (2010). For the purposes of the simulation, we also assemble the 3D velocity and density model of the crust for the city of Zagreb and its surrounding region. The model consists of a detailed description of the main geologic structures that are observed in the upper crust and is embedded within a greater regional EPCrust crustal model (Molinari and Morelli, 2011). To test and evaluate its performance, we apply the hybrid technique to the Zagreb March 22nd 2020 Mw = 5.3 event and four smaller (3.0 &lt; Mw &lt; 5.0) events. We compare the measured seismograms with the synthetic data and validate our results by assessing the goodness of fit for the peak ground velocity values and the shaking duration. Furthermore, since the 1880 Mw = 6.2 historic earthquake significantly contributes to the hazard assessment for the wider Zagreb area, we compute synthetic seismograms for this event at two different hypocenter locations. We calculate broadband waveforms on a dense grid of points and from these we plot the shakemaps to determine if the main expected ground-motion features are well-represented by our approach. Lastly, due to the events that occured in the Petrinja epicentral area at the end of 2020, we decided to extend our 3D model to cover the area of interest. We will present the preliminary results of the simulation for the December 29th 2020 Mw = 6.4 strong earthquake, as well as our plans for further research.&lt;/p&gt;

scholarly journals Traveling ionospheric disturbances triggered by the 2009 North Korean underground nuclear explosion

2015 ◽  
Vol 33 (1) ◽  
pp. 137-142 ◽  
Author(s):  
X. Zhang ◽  
L. Tang
Keyword(s):  
Acoustic Waves ◽  
High Frequency ◽  
Ionospheric Disturbance ◽  
Low Frequency ◽  
Ionospheric Disturbances ◽  
Underground Nuclear Explosion ◽  
Dual Frequency ◽  
International Gnss Service ◽  
Acoustic Gravity Waves ◽  
Traveling Ionospheric Disturbances

Abstract. Underground nuclear explosions (UNEs) can induce acoustic-gravity waves, which disturb the ionosphere and initiate traveling ionospheric disturbances (TIDs). In this paper, we employ a multi-step and multi-order numerical difference method with dual-frequency GPS data to detect ionospheric disturbances triggered by the North Korean UNE on 25 May 2009. Several International GNSS Service (IGS) stations with different distances (400 to 1200 km) from the epicenter were chosen for the experiment. The results show that there are two types of disturbances in the ionospheric disturbance series: high-frequency TIDs with periods of approximately 1 to 2 min and low-frequency waves with period spectrums of 2 to 5 min. The observed TIDs are situated around the epicenter of the UNE, and show similar features, indicating the origin of the observed disturbances is the UNE event. According to the amplitudes, periods and average propagation velocities, the high-frequency and low-frequency TIDs can be attributed to the acoustic waves in the lower ionosphere and higher ionosphere, respectively.

EM COUPLING, ITS INTRINSIC VALUE, ITS REMOVAL AND THE CULTURAL COUPLING PROBLEM

Geophysics ◽  
1975 ◽  
Vol 40 (5) ◽  
pp. 831-850 ◽  
Author(s):  
Jeffrey C. Wynn ◽  
Kenneth L. Zonge
Keyword(s):  
Electromagnetic Induction ◽  
Electromagnetic Coupling ◽  
Intrinsic Value ◽  
Low Frequency ◽  
Induced Polarization ◽  
Electrode Polarization ◽  
Electrically Conductive ◽  
Coupling Problem ◽  
Complex Resistivity ◽  
Deep Sounding

The induced polarization method of geophysical prospecting has been in use for more than 25 years with varying degrees of success. Until recently, its two principle drawbacks were (1) the inability to distinguish between anomalous rock responses and, (2) inability to distinguish between these rock responses and inductive coupling. The first problem was solved by K. L. Zonge in 1972. Solutions to the coupling problem go back to 1932, and have been expanded and elaborated upon by successive authors since then. In most of these papers, electromagnetic coupling was separated into two functions, here designated as P, a purely inductive term, and Q, a grounding or purely resistive term. This paper extends this work into a study of the reflective coupling contribution and the effects of anisotropy. Two immediate results are: (a) the development of an ultra‐low‐frequency deep sounding technique for highly conductive overburden environments, and (b) a successful iterative technique for the removal of coupling from complex resistivity field data. A study was made of the effect of electrically conductive pipelines on induced polarization and complex resistivity data. It appears that the so‐called “pipeline effect” is a composite of several effects, including current focusing nonlinearities, electromagnetic induction, and complex electrode polarization. The pipeline effect is generally predictable, while the effect of a fence or an irregular conductive inhomogeneity is not as simple.

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