Study On Active Source Character And Weak Signal Detection In Reginal Scale Deep Exploration

Seismic waves can spread through the Earth's interior, and it's the most effective means to explore Earth's interior information. The 4D map of regional structure of deep earth provides important information for earthquake prediction and understanding the continental geodynamics. Suitable seismic source and advanced recording and processing systems are necessary to produce the 4D map. Although natural earthquakes can release huge amounts of energy, the epicenters of natural earthquakes are not accurate enough to be used regional scale exploration. Artificial seismic signal is inspired by the artificial source; it is highly controllable and repeatable. These characteristics are the main difference between artificial source and natural seismic. Seismic radar built using artificial seismic source can help people observe underground state and structure initiatively; it has major significance for detecting underground structures and changes, understanding the mechanism of disasters, and studying physical forecast of earthquake. Energy of artificial source is very low. How to improve the detection ability and detection range of artificial source is very important scientific question.As active seismic source has low energy, its detecting ability is limited. We study the problem in active seismic source exploration from source character and signal detection. Explosion is the most common source for seismic exploration on the land. Traditionally, explosives are used as the seismic sources for exploring deep structure. However, explosives are expensive and have a large negative effect on the environment, so it is difficult to use them. Small explosive can be used as the seismic source for deep structure exploration if the source and receiver conditions are good enough.The airgun is the most important seismic source in marine exploration. We study energy spectrum, detection range, repeatability, and other features of high-capacity airgun firing in the reservoir. Energy of single airgun is equivalent to 1.4-1.6kg of explosives. Signal of high-capacity airgun include abundant low-frequency energy, single-shot signal can transmit to 120km. Airgun source is eco-friendly, economic, high controllable and high repeatable seismic source. It is a very useful source for regional studies. Interface can change the signal from airgun. In deep exploration, seismic waves should have enough transmission capacity to meet the requirements of the deep exploration, and help people get more information on the reflector.People use large-capacity airgun or airgun array in deep exploration. In this paper, We study simulating airgun wavelet signal, and making some amendments for high-capacity airgun. Through our study, we find that bubble pulse has more low-frequency components than pressure pulse. In deep structure exploration we should increase bubble pulse to increase low-frequency energy output. That's the key point for airgun design and parameter selection. We analyze the influence of work parameter such as airgun volume, work pressure and set depth to airgun signal. Airgun wavelet signal and its spectrum analysis from numerical simulation showed that numerical simulation can help us design airgun array to meet the actual needs. It is an important method for actual exploration.Improving the SNR of seismic records and extracting effective seismic signal is the basic work for seismic data process. Adaptive noise suppression method can effectively suppress noise, and the methods can overcome the shortcomings of the whole filter. Mutual information method can clearly mark out the tested signal and help us analyze and process seismic data automatically.Make full use of controllability and repeatability of the artificial source, based on modern information theory and approach, we study how to use seismic signal process to guide the design, inspiring mood, and signal observation of artificial source to improve detection ability and distance of active source. This is the cross field of seismology and modern information science.We combine inspiring method and signal detection, and use the following inspiring method, inspiring small shot in big shot area, a number of small shot excitation, as well as coding inspiring methods. We analyze the data-processing methods for the three shooting mode, including cross-correlation, N-th root weighted stack, phase weighted stack, as well as coding technology.