Study Of Seismic Wave Travel Time Variation In Qilian Mountains Area Using Active Source

The measurement of seismic wave travel time variation is very important to the research of the structure and physical properties of the earth and the understanding of the seismogenic and earthquake mechanism,it also has important scientific significance for earthquake monitoring.Air gun active source detection is an innovative method for the research of crust medium and its wave travel time variation because of it has highly repeatable source,precise travel time obtaining and environmentally friendly triggering.Qilian Mountains active source system of Gansu Province is located in the hinterland of the Qilian Mountains on the northern of Qinghai-Tibet Plateau.The observational network of Qilian Mountains active source system covers the Qilian Mountains seismic belt almostly,therefore,it is important to study the seismic wave travel time variation for understanding the deep tectonic activity and the seismic risk in the Qilian Mountains area using Qilian Mountains active source.In this paper,we analyze and study the method of the active source data processing,including data conversion and database management,data reliability and consistency analysis,seismic wave travel time variation obtainning.Based on the processing of the data of Qilian Mountains active source,the main results and conclusions are as follows:1.A sharing database is established to ensure data reliability.ArchiveAirGunData software(Wang WeiTao et al.)is used to integrate the data of original database of Qilian Mountains active source while the message of time,latitude and longitude is checking also.Therefore,the problem of the offset of the waveforms caused by instrument breaking,and data retrieval error caused by the replacement of the instrument is solved.The sharing database is convenient for data retrieval and interception.2.The data integration software(ReftekData2Evt)has been developed,which meets the needs of rapid seismic phase analysis and improves the efficiency of data utilization.Using this software,the original waveform data of multiple stations can be quickly integrated into EVT data format which is convenient to analyze seismic wave phase with MSDP software.3.It is verified that the variation of seismic wave travel time obtained by different data is consistent.Through the correlation analysis of the waveform data of different instruments,the contrast of the noise power spectrum density function,and the seismic wave phase arrival time analysis of different sampling rate data,it is proved that the accuracy of the travel time variation obtained by different instruments and different sampling rates are both consistent.This conclusion paves the way for the study of spatio-temporal evolution and attenuation characteristics of Qilian Mountains area.4.According to the data processing,the seismic wave travel time of the ZDY38 station and HuaJian station which is near the seismogenic area of Men Yuan Ms6.4 earthquake in January 21,2016 changed abnormally before and after the earthquake,this maybe reflects the change of the physical property in the source area before and after the earthquake.5.The PGA logarithm value of P wave of Qilian Mountains active source and the logarithm of the epicentral distance can satisfy the linear distribution.The linearity of the ground motion attenuation analyzed by the data of stations distribution along the fault is better,and the amplitude of the signal is relatively large.The results of this paper have a certain reference for the construction and development of the active source in China,especially in data processing of the active source.