Variations of Atmospheric ELF/VLF Radio Noise Due to Seismogenic Modifications in Tropospheric Conductivity

We suggest a possible explanation of the influence of pre-seismic activity on the registration rate of natural ELF(extremely low frequency)/VLF(very low frequency) pulses and the changes of their characteristics. The main idea is as follows. The distribution of the electric field around a thundercloud depends on the conductivity profile of the atmosphere. Quasi-static electric fields of a thundercloud decrease in those tropospheric regions where an increase of air conductivity is generated by pre-seismic activities due to emanation of radioactive gas and water into the lower atmosphere. The electric field becomes reduced in the lower troposphere, and the probability decreases of the cloud-to-ground (CG) strokes in such “contaminated” areas. Simultaneously, the electric field grows inside and above the thunderclouds, and hence, we anticipate a growth in the number of horizontal and tilted inter-cloud (or intra-cloud) (both termed as IC discharges) strokes. Spatial orientation of lightning strokes reduces vertical projection of their individual amplitudes, while the rate (median number strokes per a unit time) of discharges grows. We demonstrate that channel tilt of strokes modifies the spectral content of ELF/VLF radio noise and changes the rate of detected pulses during the earthquake preparation phase.

Electrical properties of dry polycrystalline olivine mixed with various chromite contents: Implications for the high conductivity anomalies in subduction zones

Chromite,a crucial high-conductivity mineral phase of peridotite in ophiolite suites,has a significant effect on the electrical structure of subduction zones.The electrical conductivities of sintered polycrystalline olivine containing various volume percents of chromite(0,4,7,10,13,16,18,21,23,100 vol.%)were measured using a complex impedance spectroscopic technique in the frequency range of 10^(−1)-10^(6) Hz under the conditions of 1.0-3.0 GPa and 873-1223 K.The relationship between the conductivities of the chromite-bearing olivine aggregates and temperatures conformed to the Arrhenius equation.The positive effect of pressure on the conductivities of the olivine-chromite systems was much weaker than that of temperature.The chromite content had an important effect on the conductivities of the olivine-chromite systems,and the bulk conductivities increased with increasing volume fraction of chromite to a certain extent.The inclusion of 16 vol.%chromites dramatically enhanced the bulk conductivity,implying that the percolation threshold of interconnectivity of chromite in the olivine-chromite systems is-16 vol.%.The fitted activation enthalpies for pure polycrystalline olivine,polycrystalline olivine with isolated chromite,polycrystalline olivine with interconnected chromites,and pure polycrystalline chromite were 1.25,0.78-0.87,0.48-0.54,and 0.47 eV,respectively.Based on the chemical compositions and activation enthalpies,small polaron conduction was proposed to be the dominant conduction mechanism for polycrystalline olivine with various chromite contents.Furthermore,the conductivities of polycrystalline olivine with interconnected chromite(10-1.5-100.5 S/m)provides a reasonable explanation for the high conductivity anomalies in subduction-related tectonic environments.

Research on earthquake prediction from geomagnetic pulsation

This paper has presented a research on the method of using digitized data of geomagnetic pulsation observation to predict earthquakes and the research results.According to the theory of inductive magnetic effect,the observation of geomagnetic pulsation events can detect the preseismic conductivity and structure anomalies of subsurface media more effectively than the conventional geomagnetic observations,especially the short-impending anomalies before earthquakes.Our research results have also indicated that the geomagnetic pulsation transfer function has obvious short-impending anomalies and typical anomaly forms before earthquakes.Using the proposed method,satisfactory prediction results have been obtained.