Ultra-shallow Seismic Data Efficient Acquisition,high Resolution Processing And Interpretation

High-resolution seismic reflection techniques are used for resolving a wide variety of engineering and environmental problems.Although instrumental developments and data processing have advanced very rapidly over the past few decades,a time consuming and costly aspect of 2D and 3D seismic surveys continues to be the acquisition of sufficiently high-fold data.The properties of geophones are important factors for high-resolution seismic exploration and have great influence on data quality.In this study we will address the problems of ultra-shallow seismic data acquisition,processing and interpretation as well.The purpose of our study is to evaluate the applicability of using different seismic geophones and processing techniques,to detect a thin burnt soil layer about 20 cm in thickness under a depth of about 2 m and determine the bottom of an artificial hill in Mojiaoshan at Liangzhu archaeological site,Southeastern China.We have collected seismic data with two kinds of geophones,normal geophones with different natural frequencies inserted into the ground and cable geophones(TD-Streamer,amphibious towed detection string)contacting the earth surface without planting,we have tried this new kind of the geophone,to increase the speed and efficiency of ultra shallow seismic surveying and thereby decrease acquisition costs also to improve the resolution compared with the normal geophone.Major advantages of this innovative approach to shallow seismic data acquisition were:have broad frequency bandwidth 20Hz to 16KHz,no need to plant geophones as the cable was equipped with takeouts for 24 geophones at 0.5 m or 1 m intervals,no need to lay out seismic cables manually just by dragging the cable the geophones work as a set which leads to increasing acquisition speed and reducing field personnel.Three stacked seismic reflection profiles have been obtained from the two kinds of geophones 60 Hz,100 Hz and cable geophone.After frequency analysis,we found out that each geophone have advantage in a specific period of frequency,we considered combining these frequencies advantages of three different kinds of geophones to broaden the effective bandwidth of the acquired data to improve the resolution.To achieve this,we designed a partial frequency match filtering method in data processing which helps to improve the resolution of seismic reflected data.The result of stacking profiles shows that match filtering is effective in detecting a thin burnt layer which distributed in the east and east south part of the studied area.Picking and identification of three reflectors has been done from the final stacked section.First reflector was the thin burnt layer,its depth ranged between 2 to 2.8 m,second reflector was the Rammed earth which picked in all the sections,its depth ranged between 5 to 7 m and increased towards the center.The last reflector is the interface between artificial and natural accumulation,its depth is between 12 to 14 m which represent the bottom of the artificial hill in Mojiaoshan.