Preliminary Application Of Airgun Source Signal In Hutubi,Xinjiang

With the development of seismological technology, diversified observational materials and rich data accumulation, researchers can investigate the medium change interior of the earth not only relying on natural earthquake, but also through the better use of rich noise data, doublet earthquake and active seismic sources. Indeed, the seismic wave generated by earthquake has been regareded as the most effective approach for studying the interior of the earth, where the variation of stress is estimated by the change of wave rate, since the change of which usually indicates the reflection to the stress variation of the earth inner medium. Recent year, thanks to the advantages of air gun source, such as high efficiency, environmental protection, low frequency and good reproducibility, which are very appropriate for detection-related application research in land area scale, the research related to active seismic based on air gun source in land area has been paid more and more attention.Based on the above, this thesis aims to explore the preliminary application research based on the air gun source in Hutubi, Xinjiang. Specifically, the provocation test was began in August, 2013 by using the joint receive between fixed station and flow station, and the preliminary study in early stage shows that the air gun source in Hutubi Xinjiang has the advantage of low frequency, good reproducibility and environmental protection and has accumulated rich data which provide solid foundation to the further research work. The preliminary application research has been carried out by using the cross-correlation detection technology to extract the travel time variation of both flow station and fixed station. With the help of the load-unload response ratio theory, some preliminary conclusions can be obtained and summarized as follows.(1) Based on the double earth crust model with “3400 travel timetable”, we compared the seismic phase of natural earthquake with air gun source depending on the theoretical seismic phase travel time. We observe that the P wave seismic phase of air gun source is clear, and its amplitude is larger than the S wave amplitude which is entirely different with the characteristics of the seismic phase of natural earthquake. However, when the epicentral distance reaches to a certain value, there appears similarity between natural earthquake and air gun source. For example, the Bei Tashan station has recorded relative clear seismic phase of both natural earthquake and air gun source because of the further distance to the epicenter, seismic phase characters is similar with that of natural earthquake. Specially, the difference and similarity of seismic phase between natural earthquake and air gun source are caused by two reasons, on the one hand, there has essential difference between natural earthquake and air gun source, and the energy caused from air gun is smaller than that of natural earthquake. On the other hand, the identification of seismic phase will be influenced by relevant factors like propagation path and stations.(2) Reflected wave radial which is propagated in the medium above specific interface brings rich medium information, and the seismic phase of reflected wave may have benefit to the research of medium properties anomaly variation in seismogenic zone before the earthquake. The travel time change of the seismic phase of PmP reflected wave recorded by Shi Hezi station, Shichang station and Wusu station have been selected to study the temporal variation characteristics of wave velocity changes twice before the 5 magnitude earthquake. From the time characters, the PmP travel time changes of the above three stations all appear abnormal process with low value in different degree continuing about four months and two months before 5 magnitude earthquake two times, and the relative rangeability of travel time change is about 0.1% to 0.26%. The abnormal characters of Shi Hezi station and Shichang station which are close to epicenter are more obvious than that of Wusu station which is far from the epicenter. From the spatial characteristic, the wave rate appears high velocity anomalies in different degree before about 5 magnitude earthquake, and the duration time is more consistent with time-distance graph.(3) The preliminary application research of load-unload response ratio should be tried to carry out. And the characteristics of load-unload response ratio Y can be analyzed by selecting three fixed stations and three flow stations and making the travel time as responses. For continuous loose time, there has no big earthquake in research area, and the value of load-unload response ratio Y represents fluctuating change around the value 1, compared with random sliding ratio, the value of Y is more reliable and stable. For the variation characteristics of Y in three fixed station where travel time variation is selected as responses, before twice about 5 magnitude earthquake, the value of Y shows different degree abnormal high value, whose occurrence time is consistent with time-distance curve of travel time change corresponding to three stations. Futhermore, the high value abnormal characteristics of Y in Wusu station is obviously higher than other two stations, and the load-unload response ratio Y got before 5.0 magnitude earthquake in Shawan is more obvious than the value of Y got before 4.8 magnitude earthquake in the same place. The system is in stable stage, thus the change of load-unload response ratio, and the value of Y changes around value 1. When the crust medium is on the stage of earthquake preparation, the value of response ratio increases gradually, and the earthquake occurs in the decrease process of Y, until the earthquake is end, the value of Y returns to 1 around. The area stress gets released and the level of total stress is low, and the change of value Y is stable. Because it is the first exploration about the load-unload research seeing the travel time of air gun source as responses, there still needs to do further works to search suitable seismic phase window and station for the application research on earthquake prediction.The active source in Hutubi Xinjiang is the first testing ground using man-made water, where the active detection of air gun source provide not only exact seismic wave source to the exploration of geologic structure in Tianshan orogenic belt, but also a good foundation to explore the research of realizing the medium continuous monitoring and genesis of strong earthquakes.