Research On Ultra-Shallow Seismic Exploration For Urban Active Faults In Urumqi City

The ultra-shallow range of depth about 200m below the ground surface is exactly the blind area of every kind of deep and shallow seismic exploration ,but it palys a important part in the research of active structure. To study canonical acquisition and processing technique of ultra-shallow seismic data for detecting urban active faults in Urumqi is provided with great typicality and applied value, and can support vital reference for detecting urban active faults in Urumqi and other areas of all the country in detecting environment similar to Urumqi in the future.This paper tries to start from the point of view of detecting urban active faults, applies related theories and methods of geology and geophysics, probes into the precondition to acquire efficient ultra-shallow seismic results in complicated geological background, studies typical seismic profiles of main active faults in Urumqi, strives to make some development in data acquisition technique,data processing and interpretation methods of ultra-shallow seismic exploration for urban active faults.Through the study,this paper gets the cognitions and conclusions below:1. By analyzing seismic data of Urumqi city, it is found that to select proper surveillance layout is one of the keys to acquire authentic exploration results in ultra-shallow P-wave reflection exploration. First, the least and most offsets should be selected properly, according to the expanding spread experiment and the principles to select surveillance layout parameters. In ultra-shallow seismic exploration, it is so hard to distinguish between reflection wave and disturbance wave in the traces near to the source, so they can be distinguished only in the condition of certain offset. At the same time, the most offset can be not too long, since the target depth is very shallow, if spread length is too long , the refraction wave will be recorded in most traces. So the short spread and small geophone group interval are needed to be applied to make data acquisition. According to the condition that the depth of Quaternary deposits is very shallow in research area, to apply 6-12 stacking folds can satisfy the requirement to get the exploration results with high-resolution and high-SNR . Otherwise, if the resolution of ultra-shallow seismic data is expected to improve, the small shot interval should be applied.