The Technology Of Seismic Exploration In The Exploration Of Active Fault In Cities

In last few years, the detection and research of active fault in city work all over the worldquickly. Detecting the active fault location, depth effectively, can avoid the direct damage of theconstruction on ground caused by active fault. In this way, influence of the near-surface strongground movement will be reduced. So doing this job reduces earthquake damage actively andeffectively. The geophysical method of shallow seismic reflection method is commonly used in thedetection of city active fault. However, in some specific area the seismic reflection cannot actionthe properties of the Material underground effectively, and became difficult to the project. Thetomography technique of first-break refraction, using first arrival travel time information hidden inthe reflection data, can get the speed attributes underground, which is in useful to exploration ofthe active fault in city.The article discusses the technology of Seismic Exploration in each step. The paper firstintroduces the basis principle of seismic exploration. Secondly, respectively discuss thetechnology in reflection wave seismic exploration and the first arrival travel time topographicimaging through the following part——the principle, the acquisition of seismic data, the dataprocessing, data interpretation. Thirdly, illustrate the factors which influence the effect in eachstage of the exploration, interpretation of the links in the main factors and technology;For city active fault exploration, high quality seismic data acquisition is prerequisites for goodexploration result. Vibroseis of seismic, can choose different scanning parameters as area situationchanges, and get the seismic record, which both maximum suppress the interference wave anddoes not reduce the effective wave. Seismic instrument, which has the advantages of highsensitivity, large dynamic range, and the ability of real time correlation function of digital, caneffectively suppress the interference and digitize the seismic data in the collection station for thetransmission process is not introduce noise and improve the seismic acquisition technology.For the first-arrival travel-time tomography technique, it is the accurate velocity pickup andhypothesis of Speed initial model that influence the results of most. Practice has proved that in theabsence of velocity data, the selection gradient of velocity model is more reliable for better theinversion result.Joint exploration of the two methods can make full use of seismic data and improve theexploration accuracy and economic benefits. First-arrival travel-time imaging, can obtain velocitystructure in a certain depth of underground by Inversing seismic travel time. It compensates thedisadvantage of reflection seismic exploration, which cannot get good results on surface orshallow layer because of the low speed on surface. Joint exploration of the two methods greatlyimproves the accuracy of prospecting. The apply the joint exploration of the two methods in the actual project, achieved good results.When the reflected wave exploration effectiveness of first-arrival travel-time tomography ofvelocity structure can be reflected wave data to provide more accurate velocity information; Whenthe reflected wave cannot effectively react the stratification, the velocity profile and the reflectiontime section can confirm each other, complement each other and get better results; When there’s asmall fault,which the reflection profile cannot response effetely, speed structure diagram canprovide velocity transformation as an explanation of the important basis. the joint exploration ofthe two methods has obvious advantages and good application effect. It has important value topromote.