Study On Accurate Measurement Method Of Seismicity Parameters Under Encrypted Observation

In this paper,we have studied three key problems in seismic monitoring and prediction for specific target areas and accurate determination of seismicity parameters.The first part is the difference of magnitude measurement in different networks.The second part is the subjectivity of the calculation rules for seismicity parameters,and the last part is the arbitrary arrangement of mobile encryption network in key monitoring region.The choice of the research area is the Shimian-Mianning-Xichang with strong seismic activity,where there are fixed seismic network and mobile seismic network.In this area,we have carried out theoretical method construction and technical research on these three key issues.Firstly,it is difficult to fuse the magnitude measurement results of encrypted mobile network with those of fixed network.We have not only developed magnitude correction formulas based on statistical seismology,but also obtained magnitude correction results by synthesizing various networks.We compare the magnitude data of Xichang mobile networks with that of fixed networks.Through sequence number of magnitude analysis and Akai information criterion?AIC?,we find that there is a linear relationship between fixed network and mobile network in magnitude determination.Starting from the probability density function of magnitude deviation and combining with Bayesian principle,we derive a magnitude correction formula under the mean and standard deviation of magnitude recorded by a mobile network and fixed network.Then,the magnitude correction formula is extended to the case where multiple mobile networks exist simultaneously,and the calculation and operation steps of practical application are also given.For our research area,the magnitude correction results show that the magnitude measured by Xichang mobile array are smaller on the whole,and the magnitude measured by fixed network are distributed near the corrected magnitude in a certain standard deviation range.The magnitude correction algorithm based on statistical seismology can comprehensively consider the magnitude difference caused by many factors to provide accurate data for seismic activity calculation,such as the difference of the site condition,the difference of the calibration function of magnitude,the experience of manual picking up seismic phases and so on.Secondly,in order to obtain reliable seismicity parameters,we apply the idea of a data-driven approach to seismicity parameter calculation and propose a parameter-free method to estimate the spatial distribution of parameters for the OK1993 model,which is currently widely used and expressed in continuous function form.To verify the feasibility of this data-driven approach and to explore the rules of model selection,we generate a synthetic catalog according to three sets of different parameters for the OK1993 model and perform large-scale calculations and method testing.In the calculation,we use a total of 5049000 randomly generated models with a various numbers of Voronoi nodes ranging from 2?100 and cell meshes generated from 1000 random throws for each number of nodes.Next we construct a penalized function to select the optimal model based on the Bayesian information criterion?BIC?.The results of the median?Q₂?and median absolute deviation?MAD?for the?,?and?values in the OK1993 model show that the initial input parameters can be well recovered for a synthetic catalog,and our calculation is optimized with an effective node number N_v=20?100 and the best 1000 BIC values.In addition,we apply this data-driven approach and corresponding model selection rules to an actual earthquake catalog in the Shimian-Mianning-Xichang region in Southwest China.The results show that the Guttenberg-Richter magnitude-frequency b values converted from the moment-frequency?values are quite different from the results obtained by previous studies using traditional methods.The low?values in the northern segment of the Anninghe fault and in the Daliangshan fault may indicate a higher stress accumulation in these regions.This new data-driven and nonparametric calculation method for the OK1993 model can provide estimations of seismicity parameters useful in many fields,including earthquake engineering,seismic hazard assessment and geodynamics.Finally,in order to overcome the influence of the arbitrary network layout on the seismicity parameter results,we apply the probability-based magnitude of completeness?PMC?method,by calculating the Detection Capability Score(D_score)and Missing Score to identify sensitive stations.Through calculating the D_score and Missing Score of 29 stations in the study area,we not only identify the stations that have the greatest impact on the seismic detection capability of the whole research area and key monitoring region,but also give the change of magnitude of completeness caused by the stations stopping operation.Taking the possible strong earthquake risk area in the northern section of Daliangshan fault zone delineated by the results of seismicity parameters as an example,we identified the sensitive stations in the key monitoring region.The results show that the stations which have great influence on the detection ability of key monitoring region are mainly distributed in the northeast of the study area.The absence of the station with the highest Missing Score in the study area will increase the magnitude of completeness in the key monitoring region by 0.3.Moreover,we also discuss the impact of the key monitoring region after several stations stop running.When two or three stations with the highest Missing Score stop running at the same time,the magnitude of completeness in the key monitoring region will increase by 0.44 or 0.60,respectively.The algorithms of sensitive station and Missing Score developed in this paper can provide scientific guidance for the rational layout of seismic network.Then it provides reliable data for the calculation of seismicity parameters.Lastly,we will obtain a technical system for accurate determination of seismicity parameters by encrypted observation with reliable basic parameters,accurate seismic parameters and reasonable layout evaluation.Therefore,this paper proposes and develops three algorithms to carry out targeted seismic monitoring and prediction for specific target areas and accurate determination of seismicity parameters,and forms a technical system for accurate determination of seismicity parameters for encrypted observation.The three algorithms are magnitude correction algorithm based on statistical seismology,seismicity parameter algorithm based on parameter-free and data-driven,monitoring layout algorithm based on Sensitive Stations and Missing Score.The solution of these three key problems and the technical system formed will provide important technical and methodological support for the scientific and effective implementation of targeted seismic monitoring and prediction in specific target areas.