Earthquake detection probabilities and completeness magnitude in the northern margin of the Ordos Block

鄂尔多斯地块北缘地震检测概率和地震目录完整性分析

The assessment of the completeness of earthquake catalogs is a prerequisite for studying the patterns of seismic activity.In traditional approaches,the minimum magnitude of completeness(MC)is employed to evaluate catalog completeness,with events below MC being discarded,leading to the underutilization of the data.Detection probability is a more detailed measure of the catalog's completeness than MC;its use results in better model compatibility with data in seismic activity modeling and allows for more comprehensive utilization of seismic observation data across temporal,spatial,and magnitude dimensions.Using the magnitude-rank method and Maximum Curvature(MAXC)methods,we analyzed temporal variations in earthquake catalog completeness,fi nding that MC stabilized after 2010,which closely coincides with improvements in monitoring capabilities and the densifi cation of seismic networks.Employing the probability-based magnitude of completeness(PMC)and entire magnitude range(EMR)methods,grounded in distinct foundational assumptions and computational principles,we analyzed the 2010-2023 earthquake catalog for the northern margin of the Ordos Block,aiming to assess the detection probability of earthquakes and the completeness of the earthquake catalog.The PMC method yielded the detection probability distribution for 76 stations in the distance-magnitude space.A scoring metric was designed based on station detection capabilities for small earthquakes in the near fi eld.From the detection probabilities of stations,we inferred detection probabilities of the network for diff erent magnitude ranges and mapped the spatial distribution of the probability-based completeness magnitude.In the EMR method,we employed a segmented model fi tted to the observed data to determine the detection probability and completeness magnitude for every grid point in the study region.We discussed the sample dependency and low-magnitude failure phenomena of the PMC method,noting the potential overestimation of detection probabilities for lower magnitudes and the underestimation of MC in areas with weaker monitoring capabilities.The results obtained via the two methods support these hypotheses.The assessment results indicate better monitoring capabilities on the eastern side of the study area but worse on the northwest side.The spatial distribution of network monitoring capabilities is uneven,correlating with the distribution of stations and showing signifi cant diff erences in detection capabilities among diff erent stations.The truncation eff ects of data and station selection aff ected the evaluation results at the edges of the study area.Overall,both methods yielded detailed descriptions of the earthquake catalog,but careful selection of calculation parameters or adjustments based on the strengths of diff erent methods is necessary to correct potential biases.

地震目录的完整性评估是研究地震活动规律的前提,一般采用最小完整性震级(MC)评估目录完整性,将低于MC的目录丢弃,检测概率可以更细致地描述地震目录的完整性,在地震活动模型构建中可以提高数据的兼容性,从而在时间、空间和震级这三个维度上更充分地利用地震观测资料。通过震级序号图方法和MAXC方法,研究了地震目录完整性随时间的变化,完整性震级(MC)在2010年之后趋于稳定,与监测能力提升和地震台网加密相关。为了探讨检测概率的估计问题,采用PMC(Probability-based Magnitude of Completeness)和EMR(Entire Magnitude Range)两种方法对鄂尔多斯地块北缘地区2010年至2023年的地震观测资料进行了分析,评估地震的检测概率和地震目录的完整性。采用PMC方法获得76台站在距离-震级参数空间的检测概率分布,并根据台站对近场中小地震的检测能力设计了评分指标进行对比,不同台站的检测能力存在较大差异。通过台站检测概率推导出地震台网对不同震级段地震的检测概率和基于概率的完整性震级。在EMR方法中,我们采用分段模型来拟合观测数据,确定了研究区域内每个网格点的检测概率和完整性震级。我们对PMC方法对样本的依赖性和低震级段失效现象进行了讨论,PMC方法对台站检测概率的低震级段可能存在高估,对监测能较弱区域的MC可能低估,两种方法的结果比较支持了这些推测。评估结果显示研究区域东侧的监测能力较好,西北侧监测能力较弱,台网监测能力在空间上分布不均匀,与台站分布有关。数据选取和台站选取的截断效应对研究区域边缘的评估结果有一定影响。总体而言,两种方法均能为地震目录提供细致的描述,但需谨慎选择计算参数或利用不同方法的优势修正潜在的偏差。