A test on methods for MC estimation based on earthquake catalog

This study tested five methods widely used in estimating the complete magnitudes(M_C) of earthquake catalogs. Using catalogs of observed earthquake properties, we test the performance of these five algorithms under several challenging conditions, such as small volume of events and spatial-temporal heterogeneity, in order to see whether the algorithms are stable and in agreement with known data. We find that the maximum curvature method(MAXC) has perfect stability, but will significantly underestimate M_C unless heterogeneity is absent. M_C estimated by the b-value stability method(MBS) requires many events to reach a stable result. Results from the goodness of fit method(GFT) were unstable when heterogeneity lowered the fitness level. The entire magnitude range method(EMR) is relatively stable in most conditions, and can reflect the change in M_C when heterogeneity exists, but when the incomplete part of the earthquake catalog is dismissed, this method fails. The median-based analysis of the segment slope method(MBASS) can tolerate small sample size, but is incapable of reflecting the missing degree of small events in aftershock sequences. In conditions where M_C changes rapidly, such as in aftershock sequences, observing the time sequence directly can give a precise estimation of the complete sub-catalog, but only when the number of events available for study is large enough can the MAXC, GFT, and MBS methods give a similarly reliable estimation.

Data replenishment of five moderate earthquake sequences in Japan, with semi-automatic cluster selection

Missing early aftershocks following relatively large or moderate earthquakes can cause significant bias in the analysis of seismic catalogs.In this paper,we systematically address the aftershock missing problem for five earthquake sequences associated with moderate-size events that occurred inland Japan,by using a stochastic replenishing method.The method is based on the notion that if a point process(e.g.,earthquake sequence)with timeindependent marks(e.g.,magnitudes)is completely observed,it can be transformed into a homogeneous Poisson process by a bi-scale empirical transformation.We use the Japan Meteorological Agency(JMA)earthquake catalog to select the aftershock data and replenish the missing early events using the later complete part of each aftershock sequence.The time windows for each sequence span from 6 months before the mainshock to three months after.The semi-automatic spatial selection uses a clustering method for the epicentral selection of earthquakes.The results obtained for the original JMA catalog and replenished datasets are compared to get insight into the biases that the missing early aftershocks may cause on the Omori-Utsu law parameters’estimation,characterizing the aftershock decay with time from the mainshock.We have also compared the Omori-Utsu law parameter estimates for two datasets following the same mainshock;the first dataset is the replenished sequence,while the second dataset has been obtained by waveform-based analysis to detect early aftershocks that are not recorded in the JMA catalog.Our results demonstrate that the Omori-Utsu law parameters estimated for the replenished datasets are robust with respect to the threshold magnitude used for the analyzed datasets.Even when using aftershock time windows as short as three days,the replenished datasets provide stable Omori-Utsu law parameter estimations.The p-values for all the analyzed sequences are about 1.1 and c-values are significantly smaller compared to those of original datasets.Our findings prove that the replenishment method is a fast,reliable approach to address the missing aftershock problem.

Inferring seismic hazard in Sichuan-Yunnan region of China based on the modern earthquake catalogue (1980-2019)

Based on the modern earthquake catalogue,the incomplete centroidal voronoi tessellation(ICVT)method was used in this study to estimate the seismic hazard in Sichuan-Yunnan region of China.We calculated spatial distributions of the total seismic hazard and background seismic hazard in this area.The Bayesian delaunay tessellation smoothing method put forward by Ogata was used to calculate the spatial distributions of b-value.The results show that seismic hazards in Sichuan-Yunan region are high,and areas with relatively high hazard values are distributed along the main faults,while seismic hazards in Sichuan basin are relatively low.

按照数量、时间、空间和震级对地震预报的综合及分项评估

在确定概率预测性能所用的评分方法中,对数似然法是最常用和最有效的。虽然对数似然得分评估了预报的综合效率,但我们需要进一步评估地震活动如总数量、发生时间、地点和震级等各因素的分项预测效率。为此,基于观测的地震事件,我们使用了条件或边际似然函数。这种分项评分揭示了预报模型的优缺点并说明了必要的改进。将这些得分应用于日本东北太平洋海岸近海MW9.0地震袭击的2011年3月灾难期间的概率预报。然而,该评估说明任何一个前瞻性预报模型都不能完全令人满意。因此,我们进行了另外两种回顾性预报试验来调查原因,包括M9巨大地震后地震活动率模式发生改变的可能性。此外,实验显示了地震可预测性研究合作实验室(CSEP)采用的单日预报规程的技术难点。进一步实验的结果引导我们对可发展为实时预报的地震可预测性研究合作实验室方案及其评估提出具体的修改建议。

Application and discussion of statistical seismology in probabilistic seismic hazard assessment studies

Earthquakes are one of the natural disasters that pose a major threat to human lives and property. Earthquake prediction propels the construction and development of modern seismology;however, current deterministic earthquake prediction is limited by numerous difficulties. Identifying the temporal and spatial statistical characteristics of earthquake occurrences and constructing earthquake risk statistical prediction models have become significant;particularly for evaluating earthquake risks and addressing seismic planning requirements such as the design of cities and lifeline projects based on the obtained insight. Since the 21 st century, the occurrence of a series of strong earthquakes represented by the Wenchuan M8 earthquake in 2008 in certain low-risk prediction areas has caused seismologists to reflect on traditional seismic hazard assessment globally. This article briefly reviews the development of statistical seismology, emphatically analyzes the research results and existing problems of statistical seismology in seismic hazard assessment, and discusses the direction of its development. The analysis shows that the seismic hazard assessment based on modern earthquake catalogues in most regions should be effective. Particularly, the application of seismic hazard assessment based on ETAS(epidemic type aftershock sequence)should be the easiest and most effective method for the compilation of seismic hazard maps in large urban agglomeration areas and low seismic hazard areas with thick sedimentary zones.