Characteristics of P and SH Waves in Shallow Seismic Reflection Surveys in the Putai Area


A 100 meter long shallow seismic line was conducted at Putai to analyze the characteristics of P and SH waves. Vertical hammer-impact was the source for P waves and transverse hammer-impact was used to generate SH waves. From walkaway noise tests, the near-offset of O wave survey was chosen at 40 m and 10 m for SH wave survey to prevent interference from surface, direct and air waves. Since the velocities of SH waves in shallow structures are considerably low, the recording time was lengthened to cover interested targets. In the P and SH final stacked results, SH wave profiles have higher revolution than those of P waves. The shallowest events detected by SH waves were 10 m in depth, which is shallower than 40 m ones of P waves, and consistent matching of reflectors indicates good correlation between P and SH wave profiles from 100 m to 230 m deep. Finally, the interval velocities of P and SH waves in the same layers were derived from processing stacking velocities, and then used to calculate Poisson¡¦s ratios for that layers. In this experiment, the calculated Poisson¡¦s ratios from 40 m to 250 m deep ranged from 0.49 to 0.46, which indicates wet and soft rocks in the shallow layers of this survey line.

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