| A multi-level fuzzy comprehensive evaluation method was adopted in this paper to establish an earthquake disaster risk evaluation model,and carries out quantitative evaluation of earthquake disaster risk of hydraulic fracturing operation areas and its adjacent 3080.25km~2 area in yibin changning shale gas development zone.Considering the comprehensive influence of geological structure,historical earthquakes and local stress accumulation in the study area,Six indicators were selected as the main evaluation factors,At the same time,three levels were established to characterize the high,medium and low earthquake risk respectively.The established model not only use a large number of original data as objective information,but also comprehensively considers expert rating as subjective judgment of experience.According to the principle of maximum membership degree,the most favorable risk evaluation was obtained in 625 grids,and then the evaluation results were optimized by weighted average and interpolation.The comprehensive evaluation map of earthquake risk was obtained by using the seismic data from 2008 to 2016 for modeling,and then the model was established by using the seismic data of 2017 for testing.The results show that most of the earthquake events in 2017 fall into the high-risk evaluation area in the comprehensive evaluation map,especially the earthquakes with a magnitude of 3 or above fall into the interpolated medium-high risk area,which indicates that the earthquake disaster evaluation model established has a certain objectivity and accuracy.The main research results are as follows:(1)The stress accumulation,historical earthquake and other induced earthquake factors were comprehensively evaluated,and their weight vector is multiplied by the membership matrix respectively.The principle of maximum membership is adopted to assess the risk of each grid and the evaluation results of single factor are labeled in625 grids.The relative single factor comprehensive evaluation map of earthquake hazard is obtained.(2)Comprehensive evaluation results of multiple factors are obtained according to the product of the weight distribution and the membership matrix in the index layer.after calculating the final score of each grid,a higher-resolution comprehensive evaluation map is obtained after interpolation by using the Kriging method.(3)In this paper,the seismic data from January 2009 to December 2016 were used for model calculation,and the corresponding seismic disaster risk assessment map was obtained.In order to verify the evaluation effect and the short-term prediction ability of seismic risk,the model was tested with the new seismic events from January to August 2017.The final results showed that the magnitude-4.3earthquake of January 18,2017 and the magnitude-4.9 earthquake of January 27,2017,which were used for the test,fell in the red region representing high risk,while the magnitude-4.2 earthquake of January 15,2017 and the magnitude-4.9 earthquake of May 4,2017 fell in the green region representing medium risk.This indicates that all medium earthquakes above magnitude 4 fall in the predicted medium-high risk zone.In addition,through statistics,it is found that 78.92%of the events in all earthquakes occurred in the high risk area,6%of the earthquakes occurred in the middle risk area,and 15.08%of the earthquakes occurred in the low risk area,which indicates that the final evaluation result has a certain objectivity and accuracy.(4)After obtaining the comprehensive evaluation map of earthquake disaster risk in the study area,the evaluation results were optimized by using grid interpolation,and the original three evaluations were converted into a number between 0 and 1,and there was a corresponding value at any latitude and longitude position in the study area.Also,1333 seismic events from January to August 2017were projected onto the comprehensive evaluation map for analysis.The results after interpolation show that 94.4%of the seismic events from January to August 2017 are located in the high risk area,and all the seismic events larger than magnitude 3 are located in the characterized high risk area.(5)In the membership classification of all factor indicators,the seismic activity rate(Z)value and the medium-high risk boundary of faults and reservoirs are relatively lack of classification basis,and the classification is highly subjective.Therefore,the sensitivity analysis of the four classification boundaries of the three factors was carried out.The Mann Whitney method and kolmogorov-smirnov method were used to evaluate the significance of the difference in the sensitivity analysis results.The results show that there is no significant difference in the evaluation results after the micro-adjustment of parameters,indicating that the original risk assessment has a certain objectivity and accuracy. |
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