نوع مقاله : مقاله پژوهشی
1 دانشآموخته کارشناسی ارشد، گروه زلزلهشناسی، مؤسسه ژئوفیزیک، دانشگاه تهران، تهران، ایران
2 استادیار، گروه فیزیک فضا، مؤسسه ژئوفیزیک، دانشگاه تهران، تهران، ایران
3 دانشآموخته کارشناسی ارشد، گروه فیزیک زمین، مؤسسه ژئوفیزیک، دانشگاه تهران، تهران، ایران
عنوان مقاله [English]
For a long time, two very important issues have been raised for humans in relation to the phenomenon of earthquakes: 1) Predicting the exact time of an earthquake, 2) Controlling the conditions caused by an earthquake. In many advanced societies, valuable work has been done on the second, which has reduced the loss of life and property, but the actions taken on the first have brought us closer to our goal. These measures include studying the tectonic activity of the Earth's crustal plates, investigating changes in wave velocity (P, S) in an area, installing sensors on the ocean floor, monitoring active faults by satellite and using Doppler shift frequency in satellites, studying the behavior of some animals and etc. The mentioned study has laso pointed out that some of them were able to inform us even 15 minutes before the earthquake.
But we are looking for a way that, in addition to being efficient, accurate and comprehensive, can cover a wider area and give us more time before the main earthquake occurs. The study of changes in the characteristics of VLF / LF waves such as signal amplitude, phase signal, temporal and spatial transmissions of the signal along the transmitter-transmitter are cases that have been followed more seriously by Hayakawa et al. since 1995. Since most of the studies have been with the help of VLF wave propagation and less LF waves have been used for investigation and pre-marking, so we want to analyze the first VLF / LF signals arrived at Tehran station in 2019 and also match them with daily density change diagrams. Electrons in terms of time obtained during the signal propagation path from the experimental IRI model associated with each month of the year. The proposed approach in this paper allows us to examine the ability of the IRI model in explaining the temporal evolution of the received signal. Here is a comprehensive way to advance IRI estimates of the current state of the ion sphere. This technique is proven to not only validate the experimental observations of recorded LF and VLF signals at the Tehran station, but also to propose a new approach for improving the estimate of the current state of the ionosphere using the IRI model. More observations could lead to a better estimation of averaged ionospheric densities along the signal propagation path at the morning and evening termination time.
By examining the changes in amplitude and phase of the signal, we examine the amount of charge density and the condition of the lower layer of the sphere ion (layer D) along the propagation path of the waves. We are looking for signs to reach a premonition for other earthquakes that will occur in the future. This approach could be used as an indicator of pre-seimic activities produced through the well-known Lithosphere-Atmosphere -Ionosphere coupling (LAIC) process. Such a methodology could lead to a solid approach for earthquake prediction in Iran using the physics-based analogy. Therefore, this study investigated a new technique for ionosphere remote sensing as well as a new approach for earthquake prediction in Iran.