Very low frequency

About: Very low frequency is a research topic. Over the lifetime, 1540 publications have been published within this topic receiving 24233 citations. The topic is also known as: VLF.

Very low frequency earthquakes within accretionary prisms are very low stress‐drop earthquakes

Abstract: [1] We report characteristic P wave spectra and stress drops of very low frequency (VLF) earthquakes that occurred within the accretionary prism along the Nankai Trough, southwestern Japan. Although many VLF earthquakes showed no distinct phases on a raw seismogram, a few showed slightly distinct phases. The arrival times of some phases were consistent with the calculated P wave arrival times. The corner frequencies of the VLF earthquakes were calculated using the stacked P wave spectra assuming an omega-square spectrum. Stress drops were very low, i.e., in the range of 0.1–10 kPa, which corresponds to 0.1%–1% of those of ordinary earthquakes. Such extremely low stress drops of the VLF earthquakes suggest that the fault strength within the accretionary prism may have weakened due to the existence of a fluid within the thrust fault system of the accretionary prism.

A survey of ELF and VLF research on lightning-ionosphere interactions and causative discharges

Abstract: [1] Extremely low frequency (ELF) and very low frequency (VLF) observations have formed the cornerstone of measurement and interpretation of effects of lightning discharges on the overlying upper atmospheric regions, as well as near‐Earth space. ELF (0.3–3 kHz) and VLF (3–30 kHz) wave energy released by lightning discharges is often the agent of modification of the lower ionospheric medium that results in the conductivity changes and the excitation of optical emissions that constitute transient luminous events (TLEs). In addition, the resultant ionospheric changes are best (and often uniquely) observable as perturbations of subionospherically propagating VLF signals. In fact, some of the earliest evidence for direct disturbances of the lower ionosphere in association with lightning discharges was obtained in the course of the study of such VLF perturbations. Measurements of the detailed ELF and VLF waveforms of parent lightning discharges that produce TLEs and terrestrial gamma ray flashes (TGFs) have also been very fruitful, often revealing properties of such discharges that maximize ionospheric effects, such as generation of intense electromagnetic pulses (EMPs) or removal of large quantities of charge. In this paper, we provide a review of the development of ELF and VLF measurements, both from a historical point of view and from the point of view of their relationship to optical and other observations of ionospheric effects of lightning discharges.

Nonlinear interaction of outer zone electrons with VLF waves

Abstract: [1] Analytical expressions have been obtained for three different types of cyclotron-resonant interaction of a test particle with a monochromatic electromagnetic wave: diffusion, phase bunching, and phase trapping. All three lead to changes in particle energy and pitch angle. They are evaluated for VLF waves and electrons at L = 5.5, to try to account for observed electron acceleration following magnetic storms. The results are that diffusion may be too slow, while phase bunching leads to deceleration. A maximal estimate of phase trapping, considered in isolation, leads to the acceleration of at least some 0.1 MeV electrons to ∼1 MeV in about 1 minute.