The seismic and geological conditions of Eastern Sichuan structure can be summarized as"adverse terrain,limestone,and steep structures",which has always been the focus and difficulty of earthquake research.With the development of physical exploration equipment,and acquisition and processing technology,the quality of seismic data in the limestone outcrop area at the top of steep structures(referred to as the limestone area)has been greatly improved.However,the signal-to-noise ratio is still much lower than that in the sandstone outcrop areas on both sides of the structure.The question of how to view the objective seismic phenomenon of low signal-to-noise ratio data in the limestone areas,whether due to insufficient earthquake research efforts or limited by the assumption of multiple earthquake coverage,must be answered urgently.Based on the analysis of the latest high-density 3D and bundle line 3D seismic data in Eastern Sichuan,starting from the basic principles of seismic exploration,combined with the model forward modeling technology and seismic data processing interpretation,we believe that the low signal-to-noise ratio seismic data in the limestone areas objectively exists,and the fundamental reason is that the seismic geological conditions in the limestone areas do not meet the assumption of multiple coverages.Three main controlling factors affect low signal-to-noise ratio data in limestone areas:1)The surface karst landforms in the limestone area from 0 to 500 m cause seismic wave scattering,generating various complex noises that rapidly absorb and attenuate downward propagating energy,resulting in weak effective reflected energy;2)The characteristics of low signal-to-noise ratio data in limestone areas are different due to the influence of different structural geometric shapes;3)Affected by the offset between inside and outside the limestone area,the seismic image quality in the upper limestone area is divided into shallow,middle and deep zones,and the data quality becomes better from shallow to deep.The article points out that in the face of the special seismic geological conditions in high and steep limestone areas,the focus of earthquake research is to improve the signal-to-noise ratio of middle and deep seismic data.
high-steep structurelimestone areamultiple coverageassumed conditionseismic datalow signal-to-noise ratio
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