Shallow Seismic Prospecting Data Acquisition and Processing Technology of Crooked-line Measurement
QIANG Zheng-yang1,2,LU Yu-xia1,2,3,CHEN Yong-ming1,2,3,MA Hai4(1.Earthquake Administration of Gansu Province(Key Laboratory of Loess Earthquake Engineering,CEA),Lanzhou, Gansu 730000,China;2.Lanzhou Institute of Seismology,CEA,Lanzhou,Gansu 730000,China; 3.Geotechnical Disaster Prevention Engineering Technology Research Center of Gansu Province,Lanzhou,Gansu 730000,China; 4.College of Marine Geoscience,Ocean University of China,Qingdao,Shandong 266100,China)
In the collection of shallow seismic prospecting data,limitations of local geological conditions prevent measurements along a straight line.To obtain high-quality seismic data,crooked-line seismic exploration can avoid obstacles and adapt to local geological conditions for shotpoint and receiver.However,due to the dispersion of offset,which influences the superposition of common reflection bin gathers and the authenticity of seismic profiles,and the shallow seismic data,acquisition and processing technology are ineffective in the crooked-line method.Therefore,it is necessary to control the quality in crooked-line seismic data acquisition and processing. During crooked-line data collection,the discrete common midpoint should be controlled within the allowable range to meet the condition of common reflection bin stacking in time and space.At some areas of large curvature,the common midpoints exceeding the range of discrete conditions should be eliminated,and the selective superposition should maintain the concurrency of each stack gathers in common bins. In the processing of shallow seismic prospecting data,the number of receivers is fewer,and the fold of data is lower than the petroleum seismic data.Therefore,time and space stack conditions of common reflection bins should be fully considered prior to the processing of shallow seismic prospecting data.Compared with regular straight-line seismic prospecting data processing,crooked-line seismic data processing is essentially the same in processing methods,processes,and parameter selection.The most fundamental difference is superposition.Crooked-line seismic data processing includes a common reflection bin stack in which several neighboring reflection points add up as a common reflection bin,while the straight-line is a common reflection point(CRP) stack.For this reason,the crooked-line's common reflection bins gathers are not strictly common reflection point gathers.Larger common reflection bins include more CRP participation in the stack,and the signal-to-noise ratio is high.Due to the average effect,however,a greater number of CRPs involved in the bin superposition results in lower resolution.Therefore,according to the geometric definition of the crooked-line method,crucial steps include selection of the common bin centerline and the common reflection bin grid during data processing in addition to and balancing the relationship between resolution and signal-to-noise ratio. By using a line measured in the Longnan mountainous area of Gansu province as an example,combined with the superposition of crooked-line common reflection bins in time and space conditions,this paper mainly analyzes the methods of control offset point dispersion range in acquisition and processing.A true and high-quality seismic section was obtained with processing by PROMAX software that showed improvement in effective wave energy,continued clarity in the events of targeted layers,suppression in all types of interference waves.These results prove that the shallow crooked-line seismic prospecting method is feasible and effective in theory and actual usage.