Study On Monitoring Wells Effectiveness Evaluation System Based On Co-seismic Response Of Well Water Level

Seismic monitoring network of subsurface fluids plays an important role in earthquake monitoring and prediction,of which especially the effect and ability for monitoring and predicting the destructive earthquake are significant.However,there are many shortages in the construction and operation of the well pattern,such as the complex regulatory level for monitoring well,the jagged structure and quality of the monitoring Wells,low sampling rate of the observation instruments,and higher data loss rate,etc.It is seriously restricted application of the subsurface fluids in earthquake monitoring and prediction.Many questions,for instance,how to choose the monitoring wells,to determine the level of earthquake monitoring changes of influence factors,and to evaluate effectiveness of monitoring wells,need to be addressed scientifically.Therefore,it is theoretically and practically significance to develop an evaluation system of the underground fluids monitoring well effectiveness.In this paper,basing on elastic theory and the strain model,choosing the monitoring wells of the completely typical tectonic units as the research object,and using the research achievements of the well level co-seismic response,attempt to adopt improved FCE-AHP method to carry out the monitoring wells efficiency quantified evaluation system research at the first time.It can be used to screening and evaluation of existing seismic subsurface fluids monitoring wells,providing a reference basis for the construction of underground fluid monitoring wells which are under construction or plan,and also has reference value to the similar phenomenon analysis in the similar block tectonic units.The main achievements of this thesis are listed as following:(1)Study on monitoring wells effectiveness evaluation method.By means of comparative analysis the expert evaluation method,multiple objective decision making method and other seven kinds of mainly comprehensive evaluation methods at present,the paper holds that the improved FCE-AHP is the most accord evaluation method with the characteristics of monitoring wells effectiveness evaluation index.Using the analytic hierarchy process(AHP)and the variation coefficient method to calculate the combination weights,and introducing the membership function to determine the fuzzy relationship matrix.The correction of the traditional method from these two aspects avoids the subjective randomness of evaluation,and also makes the evaluation result is more reasonable.(2)Study on monitoring wells effectiveness evaluation system.Stressing thewell-aquifer system as the main body of the evaluation,the process of co-seismic and precursors were analyzed for the well-aquifer system.According to the basic principles and evaluation basis of monitoring wells effectiveness evaluation,establish the monitoring wells effectiveness evaluation system based on the level co-seismic response.From three aspects of the observation background,instruments and supporting facilities and data quality,summarize the impact factors and the evaluation reference of monitoring wells effectiveness evaluation in a comprehensive way,including 29 aspects.On this basis,the evaluation index has been carried on the preliminary screening,and then select 20 quantifiable indicators which are typical and representative.Finally,establish the steps of the multi-objective monitoring wells effectiveness comprehensive evaluation,and give the selection process of the monitoring wells efficiency evaluation index.(3)Study on co-seismic response law of well water level in the typical tectonic units.Choosing north China block region as the typical area,161 underground fluids monitoring wells in this area being selected as the research object,distant-strong earthquake as the trigger condition at first,using statistics method to explore level co-seismic response law of large scale planar in the north China block region.Then the response regularity of wells is discussed near the different scale activity fault zone.As a result of minute value sampling data,the statistical result has certain limitation.(4)Analysis on mechanism factor of co-seismic water level changing in the North China block region.Regression analysis in SPSS is used to determine in the relationship between the levels changing,well seismic distance and earthquake magnitude.The level changing spectrum analysis is achieved by using matlab.It could reveal the response spectrum of the monitoring leve.Meanwhile,extract the tidal factor,amplitude ratio and phase difference by using Baytap-G program,and then analysis well-aquifer permeability variation which is caused by earthquake,and the space analysis of response sensitivity in different parts of the plot area.The co-seismic water levels fluctuations are very complicated,which can be fully reflected by the analysis results of influencing factors.Meanwhile,using a single index couldn't reveal the true response capacity of the monitoring wells for stress and strain.The research results above provided the reference basis for monitoring wells efficiency evaluation index selection in the North China block region.(5)Study on monitoring wells efficiency comprehensive evaluation in the North China block region.Combined the background information missing condition of the monitoring wells,calculating the index weight,and choosing co-seismic response rate,co-seismic response amplitude,tidal factor,distance between active fault zones and wells,distance between the interference sources and wells,observation well depth,the diameter of wells and permeability coefficient as the comprehensive evaluation index for the monitoring wells efficiency in the typical area,these eight parameters are the best caliper for reflecting the monitoring wells efficiency.The improved FCE-AHP method is used to evaluate 74 observation wells with co-seismic response which were reformed during the period of fifteen.The results show that the overall efficiency of the monitoring wells of seismic subsurface fluid in the north China block region is low.The high quality wells are very poor,and the numbers of the medium wells are the most.Therefore,aiming at the earthquake monitoring and prediction,the optimization and perfection of seismic monitoring network for underground fluid is very necessary.Due to the monitoring wells efficiency evaluation being still in exploring stage,the evaluation process of this article exist many problems,which leaded to the evaluation results have some error,such as lack of background information,more interference factors during index parameter calculation,etc.Please point out the inadequacies.