Seismic Phase Identification And Application Of The Seismic Data Acquired With The Controlled Accurate Seismic Source (CASS)

Seismic wave is regarded as a bright light to illuminate the interior of the earth.Almost all the earth's interior information,such as the physical structure,composition,state and evolution process,come from the study of seismic wave.Seismic wave is the main means to research the earth's interior.It has become an effective technical way to detect the underground structure and state actively and accurately,by using the artificial source to send seismic waves to the underground and construct a technical platform for studying the earth's interior.However,the excitation energy of artificial source is low.How to extract the accurate arrival times information of effective signal from weak signal is a key step in the using active source data to study the underground structure,also directly affects the reliability of the research results.According to the way of signal excitation,the artificial source can be divided into two types:the pulse seismic source and the continuous seismic source.While the pulse source generates an instantaneous signal with high energy,the continuous seismic source transmits the excitation signal with known time-frequency relationship to the underground for a long time and small energy.The continuous seismic source is widely used in land seismic exploration because of its advantages of environmental protection,controllable excitation and high repeatability.Several important seismological experiments have been completed in the detection of underground medium structure.It is the key and foundation to accurately extract travel times and identify the seismic phase signals from vibrator.The signals continuously excited by these artificial sources are usually variable-frequency harmonic signals.The frequencies changing with time are settable and known,which is helpful to separate seismic phase signals by filtering method,so as to improve the extraction ability of near seismic phases information.In this paper,we mainly study the identification and extraction technology of seismic phase information for the detecting data acquired with the continuous source generating sweep signal of variable-frequency and sine wave output.The research route is as follows:First,based on the extensive investigation and summary of the basic data processing methods of continuous source,we introduce the global seismic phase scanning algorithms?GSPSA?based on narrow band time-varying filtering technology.Second,we carry out the work of phase recognition,phase extraction and seismic phase verification by the GSPSA based on the detection experiment?2010?data of the controlled accurate seismic source?CASS?with 40 tons output force in Xinfengjiang reservoir area.At last,based on the simulation,the theoretical analysis of seismic phase reliability is carried out,and the applicability of this method to the variable-frequency sinusoidal sweep signal processing is further improved.Based on the above work,we implement a method of fine phase recognition for the sweep signal with harmonic output.According to processing results from the experimental data and comparative verification,the following understandings are listed as following:firstly,the GSPSA combined with time-varying narrow-band filtering technology can effectively extract effective phase information from the CASS detection records.Compared with the traditional correlation detection method,the GSPSA method can improve the resolution of the arrival times and the ability of seismic phases separation.Secondly,the phases information of Pg,Pm P,Sg and Sm S within the distance of more than200km can be effectively identified through the GSPSA method.Thirdly,for the far-field records with low signal-to-noise ratio?SNR?,the method makes it possible to separate the seismic phases with similar arrival times and overlapping,which is one of the important characteristics of between the continuous seismic source and the blasting seismic source.In order to evaluate the reliability of seismic phase information extraction,the statistical relationship between SNR of the records and the peak energy ratio of correlation wavelet,as well as the function of the time-varying narrow-band filtering and stacking technique,is studied by means of simulation calculation in this paper.The theoretical analysis can be used as a reference for the credibility and determination of seismic phases obtained by the narrow-band filtering technology and phase global scanning method.By defining the peak energy ratio of correlation wavelet?PERCW?and simulation calculation,we obtain the following main understandings:firstly,the statistical relationship between the dispersion of cross-correlation peak energy ratio and signal-to-noise ratio can be used as a method to evaluate the signal-to-noise ratio of actual observation data,and thus determine the arrival time of scanning curve obtained from experimental data processing in the same phase theory.Secondly,when the filter parameterdf₀is less than the product of frequency change rate of swept signal f_k and arrival time delay D,the two phases with similar arrival times and a certain SNR can be separated by the GSPSA method based on time-varying narrow-band filtering technology.Thirdly,it can improve the separation ability of seismic phase to increase the frequency change rate of sweep signal f_kwhen the excitation energy and excitation conditions are unchanged.Lastly,through the theoretical analysis of the reliability of seismic phase extraction,combined with the comparison of the actual observation data and the blasting data,we can determine that the identified seismic phases information of Pg,Pm P,Sg,Sm S obtained from Xinfengjiang observation data within a distance of more than 200 km is credible.The research in this paper shows that the global phase scanning method based on time-varying narrow-band filtering technology has universal applicability for extracting seismic phase information of the variable-frequency sweep signal.The time-varying narrow-band filtering technology can compress the correlation wavelet and improve the resolution of seismic phase identification,with the ability to identify the near phase of travel time,which is advantage to obtain more abundant seismic phases information and of great significance for the application of vibrator seismic source in the fine exploration and research of underground structure.