Application of apparent stress to macroseism tendency prediction in western China's mainland
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This paper takes western China's mainland(20°~50°N,73°~105°E)as an example,based on the monthly earthquake catalogue of CENC and referring to the Harvard CMT catalogue,chooses 191 earthquakes in China's mainland from January 1,1990 to December 31,2005 to compare the apparent stress value σapp1 which are calculated by using Harvard's seismic moment and magnitude-energy expressions with the apparent stress value σapp2 which are calculated by using the magnitude experiential expressions only.Based on that,this paper researched the relation between apparent stress anomalous area and macroseismic area through summarizing macroseism MS≥7 in China's mainland since1970 and graded the R-value according to the macroseism area prediction of ICD yearly prediction report.The result shows that,① When the magnitude upper limit is fixed,the variance of difference sequence between σapp1 and σapp2 increases along with the magnitude lower limit increase.In 3.5 ≤MS ≤ 6.0 sectors,the fitting degrees of σapp1 and σapp2 are better.② The change and migration of apparent stress anomalous area is possibly the reflection of the change and migration of the remarkable stress variation area in the whole structure stress area.It have many advantages,for example,the picture may directly view,it can be quantified,the prediction of area is limited and so on,which could be used to predict the microseism area.The R-value approximately is 0.35.Finally,this paper discusses the idea on the tendency prediction of macroseism area.Keywords:
Value (mathematics)
China mainland
Mainland
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Recent work on time dependent seismicity is mainly based on the so-called "regional time predictable model", which is expressed by the relation: where Tt is the interevent time, i.e. the time between two successive mainshocks of a seismogenic region, and Mp is the magnitude of the precedent mainshock. Parameter a is a function of the magnitude of the minimum earthquake considered and of the tectonic loading and c is a positive (≈0.3) constant. A problem of the method, as it has been applied till now, is its dependence on the zonation, that is, on the definition of the seismogenic regions, which is subjective to some extent. In the present work a different approach, which assumes no a-priori regionalization of the area, is attempted in order to check the validity of the model. Grids of equally spaced points at 0.5° have been created for Greece and Japan and the mainshocks located within each circle with center at a point and radius varying between 30 and 150 km were considered. When the number of mainshocks within the circle was four or larger, regression was performed and the c value was calculated. In about 75% of the cases for Greece with sufficient data and 80% for Japan the parameter c was found to be positive. This result strongly supports the validity of the model.
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Evolution of sequences of maximum earthquake magnitudes since this century in Yunnan region has been systematically analyzed in this paper.The basic variation patterns in each stage of strong-weak cycles for seismic activity have been also revealed, mechanism of which is primarily explored.It is pointed out that periodicity and strong- weak alternation of seismic activities are one of the basic features in Yunnan region.Base on this,a statistical prediction mode of similarity of multidimensional phase space for maximum earthquake magnitude in Yunnan region has been established by chaos theory. The best parameters forming a best prediction mode are also determined.Finally,the mode is used to check up the accuracy of quantitative forecastand qualitative prediction by extrapolation to maximum earthquake magnitudes foreach yearin 1 987～ 1 997.The result show that when L =1 and4 years,the average absolute errorsΔMare0 .53 and0 .4 6 respectively.The distinguishing rate for occurrence of M≥ 6strong earthquakes isf =0 . 90 ,which is higher than thatofnatural one of0 .50 .This prediction mode is stable,which can be taken as importantevidence to judge seismic tendency in Yunnan region.
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Similarity (geometry)
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We selected the Bachu-Jiashi earthquake with M_S6.8 on Feb.24, 2003 and the seismic sequence before and after the Shihezi earthquakes with M_S4.9 and M_S5.4 on Feb.14, 2003 to analyze the process of anomaly variance about the value h′ before mid-strong earthquakes. And to count on the time of appearing the anomaly peak of the value h′ and the predominance time-segment of occurring earthquakes. The result of example shows that the value h′ exists indeed some variances of anomaly fluctuation before mid-strong earthquakes. And the stronger the earthquake, the more marked the amplitude of the anomaly variance. In different area, because the intensity of the seismic activity is different, the absolute value of the value h′ isn't completely same. However, in general speaking, the value h′ will appear the discontinuity of the high value before mid-strong earthquakes. It may be regarded as one of reference judgments about the short-term prediction.
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Discontinuity (linguistics)
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The seismic correlation length prior to the Lushan earthquake(April.20,2013) has been studied by use of single-link cluster(SLC) analysis.The catalogs used were downloaded from China Earthquake Networks Center(CENC,http://www.csndmc.ac.cn).The earthquakes were located in an area centered in the mainshock(30.3N°,103.0°E) and ranging 27°~33° to 100°~106° from 5 years before the mainshock to its origin time.We selected 3.5 as the minimum magnitude and checked the completeness of the catalogs used prior to the mainshock using the Gudengberg formula,which shows good completeness above magnitude 3.5.The results showed that the growing correlation length of earthquakes for moderate-size earthquakes,which had been observed prior to the mainshock nearly two years ago to the origin time,can be fitted well by the power law.At the same time,we have developed a method to test whether or not the result obtained is simply caused by data selection to produce the desired pattern.We selected a time interval before the mainshock in which no great earthquake occurred and several years later when the greater earthquake occurred.The catalogs in the time interval will be analyzed using the same method as the catalogs prior to the mainshock study to check whether the correlation length shows an increase with the power law.We cannot find an obvious increasing process by the power law.For the preparation and occurrence stages of the earthquake process,characterized as a self-organized critical phenomenon,to test directly for growing spatial correlation lengths prior to large earthquakes is an independent approach to detect critical point behavior in observed seismicity.The results from this paper showed that the self-organized critical point characteristic was observed prior to the Lushan 7.0 earthquake.The studies in this paper illuminate the notion that the growing seismic correlation length by the power law represents a physical process of critical-point characteristics in the source area preparing for a great earthquake.In future work,the predictive power of growing correlation length should be tested.In an area,the grid search technique can be applied to extract regions of growing correlation length systematically from a data set.The estimates for occurrence time,epicenter,and magnitude of expected mainshock may then be obtained from the fitting parameter,critical region,and value of correlation length.For a further reduction of uncertainties in a predictive approach,it also appears promising to combine the concepts of growing correlation length and other predictive methods.
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After an earthquake,the earthquake disaster rapid assessment team needs very detailed information,such as an intensity distribution map.If we can study several kinds of different intensity distribution evaluation models in support of the emergency database and compare the difference between disaster evaluation results from different models,the final result will have greater credibility.In this study,the research area of focus was Chongqing and its adjacent areas.The research analyzed 19 earthquakes since 1960,collected and digitized 19 seismic intensity isoseismal maps,and acquired a total of 46 isoseismal data sets,including long axis,short axis,and total area,for a data total of 141.In accordance with the characteristics of historical isoseismals,the isoseismals were processed as ovals.In this study,the researcher looked at the epicenter distribution of earthquakes in Chongqing and the vicinity,the intensity data,and the distribution of seismic magnitude and intensity.Through regression analysis,an intensity distribution evaluation model was developed on the basis of the seismic intensity attenuation relationship,and the results from the model were compared with those from other models,which yielded a figure representing the comparison.The attenuation relationship of the earthquake in Chongqing and its adjacent area was compared with Suyun Wang,in China's eastern region;Jianqi Lu,in a moderate earthquake area,and Jiancheng Lei,in Sichuan Basin.To make the seismic intensity attenuation curve closer to the actual situation with respect to far-field and near-field intensity,additional measures were needed to improve the distribution of the data.Hence,the author developed intensity distribution evaluation models based on the length of the prolate axis and the minor axis,and area statistics.The author developed different fitting curves for(1) magnitude V long shaft fitting,(2) magnitude V short axial fitting,(3) magnitude VI long shaft fitting,and(4) magnitude VI short axial fitting.Comparisons were made with one magnitude degree above the intensity area,for the intensity I relationship,and for the length of shaft radius ratio.Last,the author used the examples to verify the above three kinds of models.The model based on the attenuation relationship and the model based on Wang Jinglai give intensity in two mutually perpendicular directions with distance attenuation,and the model based on the area is the seismic intensity distribution on the surface.The former two models are one-dimensional,and the third is two-dimensional.If an earthquake of grade IV or V happened in Chongqing and its adjacent areas,the author calculated three kinds of intensity distribution evaluation models,getting long and short axis radii.The first two models' calculation results were more closely matched and so are deemed the best by the author.Because the sample size is small,we will expand the research area in the next study to include a destructive earthquake region.Furthermore,we will include methods of data correction in the earthquake disaster loss assessment process in order to more closely approximate the true mean variance regression relationship.The shape of the intensity distribution curve was very significant for the earthquake disaster loss assessment.
Intensity
Epicenter
Sichuan basin
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We use earthquake data from 1989–1994 to test a forecast by Nishenko based on the seismic gap theory. We refer to this forecast as the “New Seismic Gap” hypothesis, because it is the first global forecast based on the seismic gap hypothesis that considers the recurrence time and characteristic earthquake magnitude specific to each plate boundary segment. Nishenko's forecasts gave probabilities that each of about 100 zones would be filled by characteristic earthquakes during periods of 5, 10, and 20 years beginning on the first day of 1989. Only the first of these can be tested now. We used three tests based on (1) the total number of zones filled by characteristic earthquakes, (2) the likelihood that the observed list of filled zones would result from a process with the probabilities specified in Nishenko's hypothesis, and (3) the likelihood ratio to that of a Poissonian null hypothesis. The null hypothesis uses a smoothed version of seismicity since 1977 and assumes a Gutenberg‐Richter magnitude distribution. We used both the Harvard Centroid moment tensor and the National Oceanic and Atmospheric Administration preliminary determination of epicenters catalogs in our test. We also used several different magnitude cutoffs in our tests, because Nishenko's forecast did not specify a clear relationship between the characteristic earthquake magnitude and the threshold magnitude for a successful prediction. Using a strict interpretation, that only earthquakes equal to or larger than the characteristic magnitude should be counted, both catalogs show only two qualifying earthquakes in the entire area covered by the forecast. The predicted number is 9.2, and the discrepancy is too large to result from chance at the 99% confidence level. The new seismic gap hypothesis predicts too many characteristic earthquakes for three reasons. First, forecasts were made for some zones specifically because they had two or more earthquakes in the previous centuries, biasing the estimated earthquake rate. Second, open intervals before the first event and after the last event are excluded in calculation of recurrence rate. Third, the forecast assumes that all slip in each zone is released in characteristic earthquakes of the same size, while in fact considerable slip is released by both smaller and larger earthquakes. The observed size distribution of earthquakes is inconsistent with the characteristic hypothesis: instead of a deficit of earthquakes above the characteristic limit, earthquake numbers are distributed according to the standard Gutenberg‐Richter relation. By lowering the magnitude threshold for qualifying earthquakes, it is possible to reduce the discrepancy between the observed and predicted number of earthquakes to an acceptable level. However, for every magnitude threshold we tried, the new seismic gap model failed the test on the number of filled zones, or the likelihood ratio test, or both, at least at the 95% confidence level.
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Moment tensor
Moment magnitude scale
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Maximum magnitude
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In this paper,we make an effort to study the feasibility to assess magnitudes of maximum potential earthquakes in sub-areas of moderately and weakly active faults in eastern China mainland by using parameters of frequency-magnitude relationship,and develop the corresponding methodology.Data suggest that frequency-magnitude relationships of fault sub-areas in eastern China mainland accord with the characteristic earthquake model,meaning that for a fault sub-area,the ratio a/b of the constants,which is also called as the maximum intercept magnitude of the exponential portion(i.e.the G-R relationship)of the frequency-magnitude relationship,is obviously less than that of the characteristic magnitudes MC.In order to make the ratio a/b be usable in indirectly assessing the magnitudes of maximum potential earthquakes in fault sub-areas,we develop a method to establish long-duration frequency-magnitude relationships for fault sub-areas by combining data of both historical and modern seismicity.In this method,event's numbers from the two sources of data are all normalized to a duration of t=500years.We then calculate at/b values of the normalized G-R relationships for 130 fault sub-areas.Our analyses reveal that maximum magnitudes,Mmax,of earthquakes occurring and recorded in the studied fault sub-areas are positively correlative with sizes of at/b values,and with the increase of at/b values the upper-limits of the maximum magnitudes,Mmax,show the feature of monotonously rising and relatively smooth variation.Based on such feature we develop three empirical formulae of the relations between the upper-limits Mmu of the maximum magnitudes,and at/b values,for the three regions,i.e.North China,Central and East China,and South China and the southeastern coastal area,respectively,and take them as empirical models to estimate magnitudes of maximum potential earthquakes in fault sub-areas.By using the newly developed method and empirical models we estimate magnitudes of maximum potential earthquakes in several fault sub-areas.Our research also suggests that several types of the abnormal seismicity,such as the swarms of moderate and small size earthquakes,aftershocks and triggered earthquake sequences,and artificially induced seismicity,as well as the determination of minimum complete magnitudes,have influences to the calculation results of at/b values,and that severely influenced at/b values are overestimated and show deflecting to the right on Mmax-at/b diagrams.The empirical models and method developed in this study can be applied to the assessment of magnitudes of maximum potential earthquakes for sub-areas of moderately and weakly active faults in eastern China mainland.
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Earthquake magnitude
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In the moment-ratio imaging algorithm,which is based on the theory of healing of a wound,the energy of each strong earthquake is distributed around the epicenter according to certain rules,and the features of the Mo-ment-ratio value R are analyzed as the space and time change,so that the relationships between the moment-ration value R and strong earthquakes can be found. In the present paper,regions divided,hypocenter depths and events completed magnitude analyses were carried out in the Chinese catalogue. By applying the moment-ratio imaging algorithm in which the parameters are adjusted,the processes of anomaly evolution which correspond to the epi-center and the surrounding value R before earthquakes of M≥7.0 since 1966 in different areas of China were ana-lyzed. It was found that the range area and imminent time of a coming earthquake could be confirmed quantita-tively by analyzing the abnormal temporal and spatial variation of the value R. The results showed that the tempo-ral and spatial variation of the value R could quantitatively reflect the temporal and spatial factors of a coming strong earthquake as well as the rule of medium rupture.
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R-value (soils)
Epicenter
Seismic moment
Value (mathematics)
Moment magnitude scale
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