Application of The Radar Technology in Forecast of Earthquake

电子科技大学 格拉斯哥学院 2017级 唐浩 同组同学：靳佳木，黄云峰
Radar, short for radio detection and ranging, means “radio detection and ranging,” which involves detecting targets and detecting their spatial position by radio. Therefore, radar is also called “radio positioning”. Radar is an electronic device that USES electromagnetic waves to detect targets. Radar emits electromagnetic wave to irradiate the target and receive its echo, so as to obtain the distance, distance change rate (radial velocity), azimuth, height and other information from the target to the electromagnetic wave transmitting point. The advantage of radar is that day and night can detect distant targets, and is not blocked by fog, cloud and rain, with all-weather, all-day characteristics, and has a certain penetration ability. Therefore, according to this feature of radar, we can use radar detection technology to achieve real-time monitoring of underground geological movement, so as to better predict the occurrence of earthquakes, so that people can better protect themselves and property security.

We know that an earthquake wave is a wave from an earthquake source that travels through the earth’s interior. Seismic waves, like other wave states, have three characteristic parameters: one is the wave speed, one is the wavelength, and the other is the period or frequency. In more cases, although a particular wave is not of a single frequency, there is one or more dominant frequencies that play a major role in the spectrum. For light waves, different dominant frequencies determine different colors, for sound waves, different dominant frequencies determine different tones, and for mechanical waves, different dominant frequencies correspond to different geological structures and movements. Therefore, we can make use of high frequency electromagnetic wave radar detection instrument to send in the form of wide-band short pulse, its working process was put in the ground by the transmitting antenna is sent into the high-frequency electromagnetic pulse wave, underground strata system structure layer can according to their characteristics such as dielectric constant to distinguish, electromagnetic when electromagnetic properties of the structure of the adjacent layer material is not at the same time, in its influence on the interface between RF signal transmission, transmission and reflection. Part of the electromagnetic energy is reflected back by the interface, and part of the energy will continue to penetrate the interface and enter the next layer of dielectric material. In the process of electromagnetic wave propagation in the strati-graphic system, transmission and reflection will occur at the interface between layers whenever different structural layers are encountered. The dielectric material has a loss effect on electromagnetic signal. So the transmitted radar signal gets weaker and weaker. The electromagnetic wave reflected from various surfaces is received by the receiver in the antenna and recorded by the host computer. Sampling technology is used to convert the electromagnetic wave into digital signal for processing. From the profile of the test results, t is obtained as the two-way travel time when the transmitter is reflected from the underground interface back to the receiving antenna. When the wave velocity of the local medium material is known, the position and depth of the target body can be obtained according to the measured accurate t value. In this way, each measuring point can be detected rapidly and continuously, and the GPR profile image can be obtained by data processing according to the waveform and intensity characteristics of the reflected wave group. Through the detection of multiple survey lines, the plane distribution of the target body of the site can be known. By analyzing the time-frequency characteristics, amplitude characteristics and phase characteristics of electromagnetic wave reflection signal (i.e., echo signal), we can get the formation characteristic information – dielectric constant, layer thickness and cavity, etc., and at the same time, we can get the characteristic dominant frequency of different movements of the same geology.

Besides that, the dominant form of seismic waves at different depths will also change:

1. For the earthquake “just under the feet” and the earthquake within a range of 100 km, it can be clearly seen that the longitudinal wave in front and the crossing wave behind and its tail wave are in front of each other. Since the distance between the source and the observer is relatively close, the high-frequency components of the seismic wave have not been attenuated. It is these high frequencies that cause damage to common buildings on the ground.
2. For earthquakes within the range of 100 ~ 1000 km, apart from the p-wave, s-wave and its tail wave, a special type of seismic wave – the first wave can be seen. The first wave appears mainly because the speed of waves under the crust is higher than the speed of waves in the crust, so the waves walking under the crust instead of walking in the crust than the waves in the “first arrival”. In addition, reflected and transformed waves from the lower crust and from the discontinuities within the crust are often seen. In some cases, you can also see surface waves that are not particularly well developed.
3. For earthquakes at a distance of 1000 km, seismic waves can be divided into two categories. Surface waves traveling along the earth’s surface have wide space to “run”, while body waves can penetrate deeper into the earth’s interior. Since the geometric attenuation of body wave is “three-dimensional” and the geometric attenuation of surface wave is “planar”, the attenuation of surface wave is naturally much slower than that of body wave. Only because the distance between the source and the seismic station is relatively large, so most of the high-frequency components attenuated, at this time the seismic wave to the long period.

Therefore，for this kind of different depth advantage frequency characteristics, we can reasonably use radar detection technology, real-time monitoring the different geological frequency under the earth’s surface, and how the frequency change, then through the analysis of data and integration, combined with the reference data and the wavelength and frequency, make the possibility of earthquake to be reasonably determined and predicted.