Research On Monitoring Capacity Of Seismological Network In Fujian Province

Seismic network is the foundation and core technology platform for earthquake prevention and disaster reduction work,providing basic data for monitoring earthquakes and carrying out earth research,and is also a useful tool for monitoring non natural earthquakes,such as mine earthquake,fire and explosion accident,underground nuclear explosion test and so on.Scientific assessment of the monitoring capability of the seismic network has become a basic and key research content.At present,many methods have been put forward at home and abroad.The calculation results are still deviant from the actual monitoring,and most of the previous studies only focus on monitoring the lower limit of the magnitude,but neglecting the response of the network to large earthquakes.When a large earthquake occurs,the amplitude saturation of the near field vibration meter will lead to the underestimation of the magnitude of the earthquake,so it is very important to study the upper limit of the network monitoring capability.This paper combines the common methods of noise level based in China and the PMC method commonly used internationally in recent years,and obtains the comprehensive analysis method to evaluate the monitoring ability of Fujian seismological network.In order to analyze the performance of the network more comprehensively,this paper also conducts a study on the monitoring of the large earthquake by the seismic network.The main research work is as follows:1.The MODE line method is used to calculate the noise level of each Seismological Station in Fujian during the larger noise period.Next we estimate the ability of the station to record seismic information,and then use the formula of near earthquake magnitude to get the complete magnitude at the grid point by dividing the grid.After the relevant interpolation calculation,the monitoring capability of Fujian seismic network based on station background noise is finally gathered.It is proved that there is a large difference between the actual magnitude and the area with complete magnitude below 0.6.2.Based on the earthquake catalogue in recent years in Fujian Province,the probability of monitoring each station for different earthquakes is calculated.Then meshes and calculates the probability of earthquake occurrence at every point of the grid.Taking the minimum magnitude of monitoring probability up to 99% as the complete magnitude,the monitoring ability of Fujian seismic network based on PMC is obtained.It is proved that the method is more accurate in the south area of the province with dense and uniform seismic distribution,and the difference between the calculated results in the north and other regions with sparse seismic distribution is large from that of the reality.3.After further analysis and comparison of the above two methods,a new method to calculate the monitoring ability of seismic network is put forward in this paper.According to the earthquake distribution in Fujian Province in recent years,PMC method is used to calculate the area with dense seismic distribution and no cluster,and other areas with sparse distribution of earthquake distribution will have large error by PMC method,so the noise method is still used to calculate the seismic distribution.This method is called the comprehensive analysis method in this paper.And the calculation results are more consistent with the actual situation than the first two methods.4.According to the response sensitivity of each station and the number of data collector allocated,the maximum ground speed recorded at each station can be calculated.By using the calculation formula of near earthquake magnitude,the minimum magnitude distribution of the seismic station network in Fujian Province when the limit of the station appears at the station,and the response of the station at the frequent earthquake area are obtained.The results show that when there is a magnitude 5.5 earthquake in the province,there will be a limitation of the station.When more than 7 earthquakes occur in areas such as the southern part of the province,more than 80% stations in the province will be limited,so that the magnitude calculation is no longer accurate,unless using peripheral stations or even stations outside the province.