Study On Wave Velocity Change Of Medium Based On Active Source Data Of Qilian Mountains

The gestation and occurrence of earthquakes are often accompanied by the change of the stress state of the underground medium,and the change of the stress state of the medium will cause the change of the seismic wave velocity.The study of the change of the wave velocity in the underground media is helpful for us to study the change of the physical properties of the underground medium,to understand the process of the earthquake,and to understand the mechanism of the earthquake.In many of the sources that use the artificial source to detect the underground medium,the large capacity airgun source has many advantages,such as high repeatability,strong energy,far detection distance,green environmental protection and so on.Based on this,the Lanzhou Institute of Seismology establishment of China's third large capacity airgun launch platform-Qilian Mountains active source air gun signal launch platform,by used in underground medium structure and change detection and monitoring in the Qilian Mountains area.In this paper,we have analyzed the characteristics of the focal point,the optimal depth of excitation and the monitoring ability of the active source air gun launcher of Qilian Mountains,on the basis of the active Qilian Mountains air gun signal transmitting platform.The calculation method based on a brief introduction to the underground medium velocity changes,from July 2015 to November 2016 Qilian Mountains active source air gun signal data were measured on the station area section of Qilian mountain received air gun signal travel time,and discuss the influence factor analysis of Qilian Mountains station active source rate change,obtain the following understanding and conclusion.1.Qilian Mountains active source air gun signal launch platform with good performance,airgun high repeatability,the best depth is 25 m,the excitation signal and the detection range and other characteristics,very suitable for the detection and monitoring of underground medium in the Qilian Mountains area.2.before the strong earthquakes in the middle of the existence of more obvious changes in travel time two.The Qilian Mountains from July 2015 to November 2016,the active air gun excited data rate change using cross-correlation detectiontechnology of area section of Qilian mountain of each station were measured,the results showed that: in 2016 2015,Qinghai Qilian Qinghai Menyuan earthquake occurred before the earthquake region stations were appeared two times relative travel time decrease(travel time reduction)that earthquake occurred at the rate change in the recovery process.A two earthquake(2016 Menyuan earthquake and Qilian earthquake in 2015,when the Pg phase obviously)and Sg seismic stations in the respective source area changes occur before and after,with synchronization and consistency when Ms5.2,Ms6.4 each phase of Qilian earthquake source area in Menyuan earthquake station changes,two times before the earthquake the minimum travel time of S wave change the rate of 13 ~ 18 ms.3.From July 2015 to October 2016 period,in addition to Qinghai and Qinghai Qilian area Menyuan underground medium velocity has obvious changes during the earthquake,the underground medium middle section of Qilian mountain area relative velocity change is relatively stable.The Menyuan earthquake source area of ZDY38 stations before the earthquake S wave average velocity relative change was 0.38%,ZDY37,S stations before the earthquake wave average relative velocity variation is0.27%,62430 stations before the earthquake S wave average velocity relative change was 0.15%,the average velocity of the S wave stations before the earthquake is about0.34% HJT.The average wave velocity of the S wave before the 63001 stations in the Qilian earthquake source area is about 0.24%,and the average wave velocity of the S wave is about before the 63005 earthquake,and the average wave velocity of the S wave is about QIL before the earthquake.The average wave velocity of each station outside the source region is between 0.001%~0.02%,and the change range is relatively stable.4.the factors that influence the variation of travel time are discussed,such as reservoir water level,solid tide and so on.The site of the Qilian Mountains active excitation source reservoir(the reservoir)water level is analyzed,the travel time caused by the change of reservoir water level maximum drop of about Ms.We conducted experiments of solid tide in September 31,2015-2015 November 5th,through calculating the P wave maximum time corresponding position and comparedwith the period of Sunan cave strain was recorded by the hole body strain,and found that the strain recorded are consistent,the maximum travel time changes of active source stations affected by the Qilian Mountains tide by about 10 ms.It is considered that the independent two earthquakes before the earthquake the focal region of each station as low value variation and the factors,which is likely due to earthquakes in the region near the fault zone of the stress state changes.