Quantitative effect of kerogen type on the hydrocarbon generation potential of Paleogene lacustrine source rocks,Liaohe Western Depression,China

Kerogen types exert a decisive effect on the onset and capacity of hydrocarbon generation of source rocks.Lacustrine source rocks in the Liaohe Western Depression are characterized by thick deposition,high total organic carbon(TOC)content,various kerogen types,and a wide range of thermal maturity.Consequently,their hydrocarbon generation potential and resource estimation can be misinterpreted.In this study,geochemical tests,numerical analysis,hydrocarbon generation kinetics,and basin modeling were integrated to investigate the differential effects of kerogen types on the hydrocarbon generation potential of lacustrine source rocks.Optimized hydrocarbon generation and expulsion(HGE)models of different kerogen types were established quantitatively upon abundant Rock-Eval/TOC/vitrinite reflectance(R_(o))datasets.Three sets of good-excellent source rocks deposited in the fourth(Es4),third(Es3),and first(Es1)members of Paleogene Shahejie Formation,are predominantly types I-II_(1),II_(1)-II_(2),and II-III,respectively.The activation energy of types I-II_(2)kerogen is concentrated(180-230 kcal/mol),whereas that of type III kerogen is widely distributed(150-280 kcal/mol).The original hydrocarbon generation potentials of types I,II_(1),II_(2),and III kerogens are 790,510,270,and 85 mg/g TOC,respectively.The Ro values of the hydrocarbon generation threshold for type I-III source rocks gradually increase from 0.42%to 0.74%,and Ro values of the hydrocarbon expulsion threshold increase from 0.49%to 0.87%.Types I and II_(1)source rocks are characterized by earlier hydrocarbon generation,more rapid hydrocarbon expulsion,and narrower hydrocarbon generation windows than types II_(2)and III source rocks.The kerogen types also affect the HGE history and resource potential.Three types(conventional,tight,and shale oil/gas)and three levels(realistic,expected,and prospective)of hydrocarbon resources of different members in the Liaohe Western Depression are evaluated.Findings suggest that the Es3 member has considerable conventional and unconventional hydrocarbon resources.This study can quantitatively characterize the hydrocarbon generation potential of source rocks with different kerogen types,and facilitate a quick and accurate assessment of hydrocarbon resources,providing strategies for future oil and gas exploration.

Global Existence and Decay of Solutions for a Class of a Pseudo-Parabolic Equation with Singular Potential and Logarithmic Nonlocal Source

This article investigates the well posedness and asymptotic behavior of Neumann initial boundary value problems for a class of pseudo-parabolic equations with singular potential and logarithmic nonlinearity. By utilizing cut-off techniques and combining with the Faedo Galerkin approximation method, local solvability was established. Based on the potential well method and Hardy Sobolev inequality, derive the global existence of the solution. In addition, we also obtained the results of decay.

Geochemical fingerprints and hydrocarbon potential of Paleocene mudrocks in the Tano Basin, Ghana: insights from biomarkers and stable carbon isotopes

The Paleocene mudrocks in Ghana’s Tano Basin have received limited attention despite ongoing efforts to explore hydrocarbon resources.A thorough geochemical analysis is imperative to assess these mudrocks’petroleum generation potential and formulate effective exploration strategies.In this study,a comprehensive geochemical analysis was carried out on ten Paleocene rock cuttings extracted from TP-1,a discovery well within the Tano Basin.Various analytical techniques,including total organic carbon(TOC)analysis,Rock–Eval pyrolysis,gas chromatography-mass spectrometry,and isotope ratio-mass spectrometry,were employed to elucidate their hydrocar-bon potential and organic facies.Thefindings in this study were subsequently compared to existing geochemical data on Paleocene source rocks in the South Atlantic marginal basins.The results indicated that the Paleocene samples have TOC content ranging from 0.68 to 2.93 wt%.The prevalent kerogen types identified in these samples were Type Ⅱ and Type Ⅲ.Molecular and isotope data suggest that the organic matter found in the Paleocene mudrocks can be traced back to land plants and lower aquatic organisms.These mudrocks were deposited in a transi-tional environment withfluctuating water salinity,charac-terized by sub-oxic redox conditions.Maturity indices,both bulk and molecular,indicated a spectrum of maturity levels within the Paleocene mudrocks,spanning from immature to marginally mature,with increasing maturity observed with greater depth.In comparison,the organic composition and depositional environments of Paleocene source rocks in the Tano Basin closely resemble those found in the Niger Delta Basin,Douala,and Kribi-Campo Basins,the Kwanza Formation in Angola,and certain Brazilian marginal basins.However,it is worth noting that Paleocene source rocks in some of the basins,such as the Niger Delta and Brazilian marginal basins,exhibit rela-tively higher thermal maturity levels compared to those observed in the current Paleocene samples from the Tano Basin.In conclusion,the comprehensive geochemical analysis of Paleocene mudrocks within Ghana’s Tano Basin has unveiled their marginal hydrocarbon generation potential.The shared geochemical characteristics between the Paleocene mudrocks in the Tano Basin and those in the nearby South Atlantic marginal basins offer valuable insights into source rock quality,which is crucial for shaping future strategies in petroleum exploration in this region.

Contamination assessment,source apportionment and associated health risks of PTEs in agricultural soil under five land-use patterns in Sanya,China

To understand the levels of potentially toxic elements(PTEs)contamination in soils and their effects on human health from different agricultural land use in Sanya,China.128 soil samples(64 topsoil samples and corresponding subsoil samples)were collected from the five representative land-use patterns.Inductively coupled plasma mass spectrometry(ICP-MS),Atomic fluorescence spectrometry(AFS),and Inductively coupled plasma optical emission spectrometry(ICP-OES)were used to determine the content of PTEs(As,Cd,Hg,Cu,Cr,Ni,Pb,Zn,Co,Mo,Sb,and V).Correlation analysis and factor analysis were used to determine the source of PTEs.Geo-accumulation index(I_(geo)),hazard quotient(HQ),and total carcinogenic risk index(TR)were used to measure the PTEs contamination and its relative health impacts.Results showed that the average values of 12 PTEs in topsoil were higher than the Hainan soil geochemical baseline,showing different degrees of PTEs accumulation effect.The concentration of PTEs in the topsoil was lower than those in the subsoil except for Cd and Hg.The I_(geo)revealed that the major accumulated element in soils was As followed by Mo.Source apportionment suggested that parent materials and agricultural practices were the dominant factors for PTEs accumulation in the topsoil.Noncarcinogenic risks of soil samples from five land-use patterns presented a trend of paddy field>dry field>woodland>orchard>garden plot.However,the HQ values of 12 PTEs were less than the recommended limit of HQ=1,representing that there are no non-carcinogenic risks of PTEs for children and adults in the study area.The TR values are within 6.95×10^(-6)-1.38×10^(-5),which corresponds to the low level.Therefore the PTEs in the agricultural soil of the study area show little influence on the health status of the local population.

Expected magnitude and distance of potential source area and the estimating method

Magnitude and distance of major potential source are needed in order to determine duration time of artificial ground motion and to determine the type of response spectrum (near field or far field) when using the seismic intensity zonation map. The magnitude probabilistic distribution function of seismic belt and the magnitude and space joint distribution function for given intensity of the site in a potential Source are provided. Then the basicformula of calculating expected magnitude and expected distance are developed. Several examples for calculating expected magnitude and expected distance in northern China are discussed. These results show that expected magnitude and expected distance are related not only to geometry of potential source and magnitude but also to the intensity of the site with certain exceeding probability.

Oil and gas resource potential of the lower members of E_(h3) in the lower Tertiary of the Biyang Depression, China

The lower Tertiary Eh3 is divided into two sections： the upper members of Eh3 and the lower members of Eh3 in the Biyang Depression. The first section is generally regarded as a key target of oil and gas exploration, but the resource potential of the lower members of Eh3 has been neglected. We have obtained new knowledge about Eh3 from comprehensive geological research. The lower members of Eh3 are high-quality and main source rocks, which have good oil and gas resource potential. This is a new direction for oil and gas exploration. The geochemistry characteristics of source rocks of the lower members of Eh3 in the lower Tertiary of the Biyang Depression were analyzed in detail. A basin modeling method was applied to hydrocarbon generation of the lower and upper members of Eh3 source rocks, the oil and gas resource potential was comparatively analyzed, and then favorable tectonic zones were pointed out. In the lower members of Eh3, a set of semi-deep lake to deep lake high-quality source rocks occurs rich in algae organisms, mainly of type II1, with a high abundance of organic matter. Most of the source rocks are just in the peak stage of hydrocarbon generation, which is a favorable foundation for forming abundant oil and gas resources in the Biyang Depression. The comparative analysis of the hydrocarbon- generation quantities between lower and upper members of the Eh3 source rocks shows that the lower members of Eh3 have good oil and gas resource potential, and the hydrocarbon-generation quantity accounts for 51% of the total in Eh3. Specifically, the oil-generating quantity accounts for 50% of the total and the gas-generating quantity accounts for two thirds of the total. Therefore, source rocks in the lower members of Eh3 of the Biyang Depression have good oil and gas resource potential, which is a key factor for future deep oil and gas exploration.

Organic petrology and hydrocarbon generation of potential source rocks in Permian formation of Junggar Basin,Northwest in China

From the outcrops in the Yaomoshan and Hongyanchi sections,oil shales,deep dark mudstones or black mudstones with better organic richness were found.Through the analysis of the samples in the organic petrology method,the microscope features of the sedimentary organic matter were studied.The results indicate that three types of kerogens present in the measured samples.Kerogen type Ⅰ consists of the laminate algainite,abundant sporinite and only little content of cutinite,which can mainly generate oil.The generation hydrocarbon components of the type Ⅱ kerogen are dominated by the sporinite,cutinite and little the exinite debris.The type Ⅲ kerogen is comprised of the sporinite and debris of the exinite with some components of gas generation.Through the analysis of the experiments,the organic kerogen of the Lucaogou formation is mostly comprised of the type Ⅰ,partially type Ⅱ,and particularly type Ⅲ.In Hongyanchi formation,the organic type is mixed by the types Ⅱ and Ⅲ.The plot of the (S1 +S2) or TOC value and the content of exinite show two trends.From the evolution of burial and the Permian source rocks in Changji Depression,the Permian formation source rock has ended the generation of hydrocarbon.A significant difference in constituents of the organic macerals among three kerogens in these samples leads to the distinction of the potential hydrocarbon generation.The Lucaogou formation for kerogen type Ⅰ has better potential hydrocarbon generation.It can reach the oil peak with Ro ratio of 0.9%.For the kerogen Ⅱ,the oil peak of the source rocks comes late with the Ro ratio of 1.0% with less quantity of the generation hydrocarbon than the kerogen Ⅰ.For type Ⅲ,it can mainly generate gas and reach the gas peak with the Ro ratio of 1.3%.In a word,the Lucaogou formation and Hongyanchi formation source rocks with high organic richness in Permian source rocks have well exploration prospects.

Interrelation between seismicity parameters and delimiting potential seismic sources in a seismic statistical region and its influence on seismic risk estimation

In the paper, we have discovered the abnormal area distribution features of maximum variation values of ground motion parameter uncertainty with different probabilities of exceedance in 50 years within the range of 100°-120°E, 29°-42°N for the purpose to solve the problem that abnormal areas of maximum variation values of ground motion parameter uncertainties emerge in a certain cities and towns caused by seismicity parameter uncertainty in a seismic statistical region in an inhomogeneous distribution model that considers tempo-spatial nonuniformity of seismic activity. And we have also approached the interrelation between the risk estimation uncertainty of a site caused by seismicity parameter uncertainty in a seismic statistical region and the delimitation of potential sources, as well as the reasons for forming abnormal areas. The results from the research indicate that the seismicity parameter uncertainty has unequal influence on the uncertainty of risk estimation at each site in a statistical region in the inhomogeneous distribution model, which relates to the scheme for delimiting potential sources. Abnormal areas of maximum variation values of ground motion parameter uncertainty often emerge in the potential sources of Mu greater than or equal 8 (Mu is upper limit of a potential source) and their vicinity. However, this kind of influence is equal in the homogeneous distribution model. The uncertainty of risk estimation of each site depends on its seat. Generally speaking, the sites located in the middle part of a statistical region are only related to the seismicity parameter uncertainty of the region, while the sites situated in or near the juncture of two or three statistical regions might be subject to the synthetic influences of seismicity parameter uncertainties of several statistical regions.

Electric Potential in Surface Produced Negative Ion Source with Magnetic Field Increasing Toward a Wall

Electric potential near a wall for plasma with the surface produced negative ions with magnetic field increasing toward a wall is investigated analytically. The potential profile is derived analytically by using a plasma-sheath equation, where negative ions produced on the plasma grid （PG） surface are considered in addition to positive ions and electrons. The potential profile depends on the amount and the temperature of the surface produced negative ions and the profile of the magnetic field. The negative potential peak is formed in the sheath region near the PG surface for the case of strong surface production of negative ions or low temperature negative ions. As the increase rate of the magnetic field near the wall becomes large, the negative potential peak becomes small.

Demarcation of potential seismic sources on integration of genetic algorithm and BP algorithm

In this paper potential seismic sources in coastal region of South China are identified by integration of genetic algorithm (GA) and back propagation (BP algorithm). GA is used for finding the best parameter combination rapidly in an infinite solution space for artificial neural networks (ANN). The results show that the distribution of potential seismic sources with different upper magnitude demarcated by this classifier is mostly satisfied the intrinsic relationship between seismic environment and earthquake occurrence, with less effect from subjective judgment of human being.

Evaluating Microbial Water Quality and Potential Sources of Fecal Contamination in the Musconetcong River Watershed in New Jersey, USA

Microbial pathogens and indicators have contributed to major part of water quality degradation in the United States. Located in the northwestern New Jersey, the Musconetcong River has been included in the New Jersey Impaired Waters List or the 303(d) List due to high concentrations of fecal indicator bacteria. Hence, a Total Maximum Daily Load plan was established to address microbial water quality issues in the watershed. The objectives of this study were to assess the current status of microbial water quality and to determine potential sources of fecal contamination in the Musconetcong River Watershed using microbial source tracking techniques. Fifteen sampling events in total were carried out at nine sites throughout the Musconetcong River Watershed in August 2016, July and August 2017. E. coli enumeration was performed to determine the possible presence of fecal contaminations. Microbial source tracking techniques, specifically Canada goose, cow, deer, horse, and human-specific molecular markers, were used for real-time polymerase chain reaction (qPCR) analysis in order to identify and quantify potential sources of fecal contamination. The results indicated that E. coli was found present at all nine study sites. Two of the nine sites violated the New Jersey Surface Water Quality Standards in August 2016, while all of the nine sites exceeded the standards in both July and August 2017. Water temperature, dissolved oxygen (DO), and specific conductance at the study sites ranged from 13.5?C to 25.3?C, from 7.7 mg/L to 13.0 mg/L, and 278.5 μS/cm to 1335.0 μS/cm, respectively, at the time of sample collection. E. coli counts were found to be negatively correlated with temperature and specific conductance (p p < 0.05). Higher percentage of presence of human, Canada goose and deer markers were observed at all fifteen sampling events indicating human and wildlife were the two major sources of fecal contaminations in the Musconetcong River Watershed. The study suggested applying restoration measures to reduce fecal contaminations from anthropogenic and wildlife sources in order to improve microbial water quality of the Musconetcong River. However, more frequent and strategic sampling plan is recommended to supply more comprehensive data to aid in future planning of best management efforts on controlling fecal contaminations.

Organic Geochemical Evaluation of Cretaceous Potential Source Rocks, East Sirte Basin, Libya

Cutting samples (n = 93) from the Sirte, Tagrifet, Rakb, Rachmat, Bahi Formations of Upper Cretaceous and Nubian Formation (Lower Cretaceous) derived from eleven wells (6C1-59, 6J1-59, 6R1-59, KK1-65, OO2-65, M1-51, KK1-65, B-96, B-95, B-99, E1-NC-59) locate in the Amal, Gialo, Nafoora, and Sarir Fields present in East Sirte Basin were analysed in the aim of their organic geochemical evaluation. A bulk geochemical parameters and evaluation of specific biomarkers by chromatography-mass spectrometry (GC-MS) implemented to find out a diversity of interbedded non-marine lithofacies including sandstones, siltstones, shales and conglomerates. Such rocks are good source and contain fair to good contented of organic matter passing in the course of very good, in which the excellent source rocks have organic carbon richness (TOC) reached to 5.16 wt%. The studied samples are ranged from gas to oil-prone organic matter (OM) of hydrogen index (HI) ranged between 115 - 702 mg HC/g TOC, related with gas prone (OM) of (HI) 300, associated with oxygen index (OI): 3 - 309 mg CO2/g TOC indicate that organic matter is dominated by Type II/III kerogen. The maturity of these source rocks is variations ranges from mature to post-mature-oil window in the Sirte and Rachmat Formations, as inferred from the production index (PI: 0.07 - 1.55) and Tmax and Ro% data (Tmax: 425 - 440/Ro%: 0.46 - 1.38) and early to mid-stage maturities for the other formations. Low PI in some samples seems to imply that the most of the hydrocarbons have expelled and migrated from the rocks. Biomarker ratios of individual hydrocarbons in rock extracts (n = 21), were also used in order to investigate the samples’ thermal maturity and palaeo depositional conditions. Pristine/Phytane ratios of 0.65 - 1.25 and dibenzothiophene to phenanthrene (DBT/P) ratios of 0.04 - 0.47 indicated Anoxic and suboxic conditions of depositional source rock. The origin of OM of the studied samples attributed to a marine algal source as indicated from the dominated by the C27 and co-dominant C28 homologues sterane in molecular composition distributions. The marine shale and carbonate lithofacies of rock samples were also indicated by high C19TT/C23TT ratio and low relative abundance of C24TeT/C23TT, consistent with their interpreted marine affinity. An organic geochemical evaluation pointed out that the Sirte Shale formation (Campanian/Turonian) is the main source rock in this petroleum area.

Study of the Non-Uniform Distribution of Earthquake Risk Within Potential Sources

Potential sources are aggregates of probable future epicenters.In this area,for source models currently,in common use for seismic risk analysis in China,the mean area of each potential source is about 3000-4000 km2.It is assumed that seismic risk has a uniform distribution within the range of each potential source,but studies have shown that the uniform distribution model to a large extent may give an underestimation of the seismic risk.In this paper,the relative distribution of historical epicenters in space within potential sources is discussed,a method is proposed to quantitatively describe the non-uniform distribution of strong earthquakes within potential sources,and some preliminary results are given.By using the results of this paper,seismic risk analysis and seismic zonation can be made more scientific and more reasonable.

Assessing the Potential Use of Solar Energy Source in Urban Areas Located in Natural Protected Sites

The main aim of this paper is to present an easy to use methodology for assessing the potential amount of electricity or thermal energy production in urban areas located in natural protected sites. The methodology is based on two different steps: a territorial analysis for the evaluation of solar radiation and usable surfaces for photovoltaic or solar thermal plant, and a plant analysis for highlighting those photovoltaic and solar thermal technologies which installation will not generate significant impacts in areas characterized by high environmental and landscaping value. The methodology was successfully applied in two case studies inside two different Italian natural protected areas. The obtained results were provided to local administrations and communities as a useful tool for sustainable energy planning.

Delineation of Potential Seismic Source Regions of Moderately Strong Earthquakes Without Seismogenic Tectonics

In this paper,approaches are developed to delineate the potential seismic source regions of moderately strong earthquakes that do not have clear seismotectonic settings.Based on comprehensive analysis of regional tectonic backgrounds and seismicity,the data,such as isoseisrnals,spatial distribution of after shocks,regional tectonic stress field,and focal mechanisms,are employed for the delineation of the potential seismic source regions.The reliability of such potential seismic source regions is also discussed.

Artificial Neural Network Method Based on Expert Knowledge and Its Application to Quantitative Identification of Potential Seismic Sources

In this paper,an approach is developed to optimize the quality of the training samples in the conventional Artificial Neural Network(ANN)by incorporating expert knowledge in the means of constructing expert-rule samples from rules in an expert system,and through training by using these samples,an ANN based on expert-knowledge is further developed.The method is introduced into the field of quantitative identification of potential seismic sources on the basis of the rules in an expert system.Then it is applied to the quantitative identification of the potential seismic sources in Beijing and its adjacent area.The result indicates that the expert rule based on ANN method can well incorporate and represent the expert knowledge in the rules in an expert system,and the quality of the samples and the efficiency of training and the accuracy of the result are optimized.

Develop an Air Emission Inventory for Potential Point Sources in Northern Key Economic Zone and Simulate Its Impacts on Air Quality in Hanoi City,Vietnam

The Northern Key Economic region of Vietnam is a dynamic economic center that is an important economic locomotive of the North and the whole of Vietnam.In this area,large industrial parks are concentrated,attracting many large FDI projects.Key industries:cement production,cars-motorcycles,electronics,...Economic development entails environmental problems.The industrial sector has been identified as the number one driving force driving the growth of Hanoi city and neighboring provinces.Therefore,industrial development is one of the main causes of environmental pollution.In addition,the growth rate of industry in neighboring provinces significantly affects the air quality in Hanoi city.Some factories in Vinh Phuc,Hung Yen,Bac Ninh and Hai Duong provinces have large sources of gas emissions,potentially affecting air quality around Hanoi city.Monitoring results show that air pollution in Hanoi city is mainly caused by dust pollution,especially PM2.5 superfine dust.This is a very harmful dust to health;it is necessary to determine the cause and control solution.Therefore,the objectives of this study are:(1)inventory of potential emissions sources for industrial activities in the northern key economic region around Hanoi;(2)Simulate air spread by AERMOD model to get an overall picture of the industrial impact of surrounding provinces in Hanoi city;(3)Propose solutions to manage air quality for the city in the coming time.Simulation results for pollutants with the highest concentration of NOx for 1 hour,24 hours and the average of the year is 7.94;1.02;0.222(μg/m3);of CO for 1 hour and 8 hours are 27.616;8.89(μg/m3);of SO2 for 1 hour,24 hours and the average of the year is 4.005;0.288;0.038(μg/m3);of PM2.5 for 1 hour,24 hours and the average of the year is 0.32;0.023;0.003(μg/m3);of PM10 in 1 hour,24 hours and year average are 1.03;0.074;0.098(μg/m3).

The Principle and Method for Delineation of Potential Seismic Sources in Northwest Yunnan

Based on the collection and analysis of achievements of other scholars, and by consulting the results of seismic safety evaluation of engineering sites and field surveys of recent years, the seismotectonic indicators are determined for northwest Yunnan and its vicinity, and then potential seismic sources are further delineated. In practice, the following principles are applied: for areas with strong historical earthquakes, the recurrence principle is used to determine the upper bound magnitude; for areas with distinct seismogenic structure but no historical strong earthquake records, the tectonic analogy principle is used in the light of the size and activity behavior of the structure; for areas where the segmentation of the active fault is well studied, the potential sources will be demarcated more precisely; and for areas with buried fault, the seismicity pattern and geophysical abnormity are used to determine the direction of the major axis of the potential seismic source.

Focal Mechanism Analysis for Determination of Potential Source Zones in South China and Its Adjacent Regions

Based on the results of focal mechanism solutions in southeastern areas of China (south of 34°N and east of 105°E), this article analyzes the correlation of focal mechanism solutions with seismogenic structures of moderate strong earthquakes and the direction of potential source zones. The data show that the nodal planes of focal mechanism solutions and the principle stresses in southern China are of predominantly similar directions, most of the solutions for M≥4.0 earthquakes correspond to the main structure directions as well as the directions of potential source zones. The statistical results of multiple small earthquakes concerning nodal planes and main stress axes are also reliable for determining the direction of potential source zones. According to the analysis of focal mechanism solutions, long-axis direction of isoseismals distribution of aftershocks, geologic structures, and seismic activity in two areas of the M_S6.1 earthquake in the south Yellow Sea in 1996 and the M_S5.2 earthquake in Fujian in 1997, the potential source zone division is discussed.

Application of Characteristics of Seismogenic Structures in the Determination of Parameter of Potential Seismic Source Areas

The characteristics of seismogenic structures are an important basis for delineating the potential seismic source areas and determining the annual occurrence rate of earthquakes. The potential seismic source area does not only have the intension that “this area has the possibility for destructive earthquakes to occur in the future" but also means that earthquakes of high magnitude interval have the characteristics of similar recurrence. When determining the seismic activity parameters of a statistical unit, some active tectonic blocks in the unit may have different background earthquakes. In order to better reflect the heterogeneity in space of seismic activities, it is necessary to divide the potential seismic source areas into three orders. By analyzing the recurrence characteristics of earthquakes of high magnitude interval in the potential source area and calculating the occurrence probability of earthquakes of high magnitude interval in the potential seismic source area in the time window for prediction, the average annual occurrence rate of earthquakes can be obtained by the method of probability equivalent conversion in the time window for prediction. This would be helpful for considering the recurrence characteristics of strong earthquakes in potential source areas within the framework of seismic risk analysis of China. Besides, the insufficient frequency of characteristic earthquakes of the next high magnitude interval in the potential source area and the heterogeneity of strong earthquakes on seismogenic structures are analyzed to see their application in seismic risk analysis.