Assessing current faulting behaviors and seismic risk of the Anninghe-Zemuhe fault zone from seismicity parameters

Using the data of regional seismic network, this paper analyzes the current faulting behaviors of different segments of the Anninghe-Zemuhe fault zone, western Sichuan, and identifies the likely risky segments for potential large earthquakes. The authors map the probable asperities from the abnormally low b-value distribution, develop and employ a method for identifying current faulting behaviors of individual fault segment from the combinations of multiple seismicity parameter values, and make an effort to estimate the average recurrence intervals of character-istic earthquakes by using the parameters of magnitude-frequency relationship of the asperity segment. The result suggests that the studied fault zone contains 5 segments of different current faulting behaviors. Among them, the Mianning-Xichang segment of the Anninghe fault has been locked under high stress, its central part is probably an asperity with a relatively large scale. The Xichang-Puge segment of the Zemuhe fault displays very low seismicity under low stress. Both the locked segment and the low-seismicity segment can be outlined on the across-profile of relocated hypocenter depths. The Mianning-Xichang segment is identified to be the one with potential large earth-quake risk, for which the average recurrence interval between the latest M = 6.7 earthquake in 1952 and the next characteristic event is estimated to be 55 to 67 years, and the magnitude of the potential earthquake between 7.0 and 7.5. Also, it has been preliminarily suggested that for a certain fault segment, its faulting behaviors may change and evolve with time gradually.

Mathematical basis,correlativity and selection of seismicity parameters

Using the analytic expression of seismicity parameters, the dependency and correlativity between the statisticalparameters and seismic frequency or seismic intensity are discussed. The statistical parameters are divided into twokinds. One kind is the regional seismicity parameter, 17 parameters are analyzed in this paper. The other kind isthe seismicity distribution parameter. They are the distribution parameters of time, space and magnitude. The existent base and rationality of distribution parameters depend on the application of distribution model. We analyzeand draw an analogy between the natural probability, Poisson, Weibull distributions and multi-f racial analyticformula in time, space and magnitude. And some examples are given in this paper. The P value and H value of aftershock sequence attenuation, the U value and F value of eanhquake swarm sequence and the entropy of information are discussed preliminarily. Another method about analyzing relationships among time-series curves aregiven. The resemblance relativity degree R,.,, and the relativity degree G,.,, of relative change slope can be usedas the determining values. At last, some preliminary ideas about sifting and using for seismicity parameters are advanced in this paper.

Interrelation among several important links in seismic risk analysis

In order to further reveal the interrelation among division of seismic statistical regions, delimitation of potential seismic sources and estimation of seismicity parameters, we select 21 representative sites located in different places within the range of 100°-120°E, 29°-42°N to study the influences of seismicity parameter uncertainties of statistical regions on seismic risk estimations of these sites in the inhomogeneous and homogeneous distribution models. Combining the results from this study and previous ones, we can see that different schemes for dividing seismic statistical regions can change the seismic data in a statistical region. The uncertain data and additional uncertainty in selecting time intervals for seismic statistics will result in uncertainty of seismicity parameters estimation in a statistical region. For the homogeneous model, the larger the variation of this uncertainty is, the greater the uncertain influence on the seismic risk estimation of a site will be, which means that the division of seismic statistical regions makes a major contribution. In a seismic statistical region, the delimitation of potential sources and variant weight assignment of spatial distribution functions can raise the estimated values of ground motion parameters in the place where great earthquake might occur and its vicinity. In these places, the influence of uncertainty in potential source delimitation is very obvious, especially on the absolute magnitude of ground motion parameters （e.g., intensity）, which means that the link of potential source delimitation makes a major effect. Generally speaking, the link of potential source delimitation affects mainly the sites located in the potential sources with the highest and second-high upper-limit earthquake magnitudes or in the vicinity of those with the highest upper-limit magnitude. While for the sites located in the potential sources with low upper-imit magnitudes, the uncertainty influence of statistical region division is larger than that of potential source delimitation.

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.

Analysis of Seismic Activity in the Middle Part of the North-South Seismic Belt——Joint Study on Deep Seismic Sounding Profile and Seismicity Parameters

Using the rich deep seismic sounding data recorded in the middle part of the NorthSouth Seismic Belt in China,the horizontal and vertical profiles are constructed to obtain the seismic velocity structure,analyze the seismic distribution and calculate the seismic energy and the thickness of the seismogenic layer at the same time.On this basis,the seismicity parameters are calculated using the earthquake catalogue of the study area for the past 40 years,and the relationship between the b-value distribution and the velocity structure is analyzed.The results show an uneven b-value distribution in the study area and a segmented feature along the Longmenshan fault zone.Most of the earthquakes occur in the transition zone anomalies from the positive to the negative.In addition,the thickness of the crust drops from ~60 km to ~48 km from the Southeastern to the Northeastern Qinghai-Tibetan Plateau,but the thickness of the seismogenic layer increases gradually.It is speculated that the crustal composition of the Northeastern margin contains more felsic materials and has relatively stronger seismic activities than the Southeastern Qinghai-Tibetan Plateau,possibly associated with the subduction and compression of the Indian Ocean Plate.

Study on Uncertainties of Seismicity Parameters b and ν_4 in Seismic Statistical Zones

For several seismic statistical zones in North China, the key factors causing uncertainties in the important seismicity parameters b and v4 and the features of their uncertainties are discussed in this paper. The magnitude of uncertainty is also analyzed. It can be seen that the key influencing factors are statistical period, methods of processing statistical samples, lower limit magnitude and the annual average occurrence ratio of large earthquakes. The variation ranges of b and v4 in the Tancheng-Lujiang zone are as high as 0.2 and 1. 4 respectively, which are similar to those in the Fenwei zone. They are much smaller however in the Hebei zone because of its sufficient statistical samples.

Identification of expected seismic activity areas by forecasting complex seismic-mode parameters in Uzbekistan

In this paper, the author proposed a methodology to reveal expected seismic activation places for coming years by a complex of forecasting parameters of a seismic mode. Areas in Uzbekistan where currently observed anomalies in various parameters of a seismic mode has been revealed. By number of displayed abnormal signs the areas has been ranked based on probability of occurrence of strong earthquakes there. It has prepared schemes of the synoptic forecast of expected seismic activation places in case of occurrence of strong earthquakes in the Central-Asian region.

The Relationship Among Bedrock Seismic Ground Motion Parameters with Different Exceedance Probabilities in the Panxi Area

Based on the calculation of the bedrock effective peak acceleration (EPA) zoning map in the Panxi area, the ratios of EPA with exceedance probabilities of 63%, 5%, 3%, 2% and 1% over 50 years to that of 10% in 50 years are 0.302, 1.30, 1.55, 1.76 and 2.14, respectively. The seismic effect will be conservative and safe if taking this zoning map as the earthquake resistant fortification level and following the relevant rules of the Code for Seismic Design of Buildings (GBJ11 89) to calculate the seismic effect. Furthermore, the main factors that influence the A10/A63 ratios have been found to be the attenuation relationship of seismic ground motion, the division of seismic potential source regions and the seismicity parameters. These achievements are helpful to the spreading and applying of the zoning map.

Evaluation of Uncertainty of Earthquake Parameters for the Purpose of Seismic Zoning of Iran

An efficient procedure is used for explicit description and evaluation of uncertainty of earthquake parameters in the uniform catalog of earthquakes in Iran and neighboring regions.An inadequate number of local and regional seismographic stations,poor station distribution,and Inadequacy of velocity models have resulted in conspicuous uncertainty in different parameters of recorded events.In a comprehensive seismic hazard analysis such uncertainties should be considered.Uncertainty of magnitude and location of events are evaluated for three different time periods,namely,historical,early instrumental,and modern instrumental time periods,for which existing seismological information differ widely in quantity,quality,and type.It is concluded that an uncertainty of 0.2-0.3 units of magnitude and 10-15 km in epicenter determinations should be considered in the most favorable conditions.None of the hypocenters of earthquakes in Iran can be considered as reliable,unless supported by other information such as

Stress triggering" between different rupture events in several earthquakes

Most strong earthquakes have complex rupture processes. As an approximation, each earthquake can be described as two or more subevents of rupture with time interval of several seconds to several days. In order to discuss the relationship between different subevents, we investigated the rupture process of the 1966 Xingtai, the 1976 Tangshan, the 1990 Gonghe and the 1996 Lijiang earthquake by calculating the static Coulomb failure stress changes produced by the first subevent. The calculation of static stress changes produced by fault slip is based on the formulation of Okada (1992). The result suggests that the static Coulomb failure stress changes (ΔCFS) produced by the first subevent have 'triggering' effect on the subsequent subevents which locate in the region where the Coulomb stress change produced by the first event is positive, with the order of magnitude 10-2 [similar to] 10-1 MPa.

Higher degree moment tensor inversion of Mani earthquake using far-field broadband recording

Breakthrough point source model, extended earthquake source model is used to calculate more seismic source parameters in this paper. We express seismic source using higher degree moment tensors, to reduce a Iarge number terms originally presenting in higher degree moment tensor representation, Haskell rupture model is used. We in verted the source parameters of Mani earthquake in Tibet using broad-band body wave of 32 stations of Global Seismograph Network (GSN), the results show that it is a strike-slip fault, rupture direction is 75°, rupture duration is 19 s, the fault plan is φ=77°， δ5=88°, A=0°, the auxiliare plane is φ=347°, δ=90°, k=178°, and the fault dimension is 47 km×28 km. These results will give new quantitative data for earth dynamics and have practical meaning for seismic source tomography research.

Research on the Characteristics of Large Earthquake Activity on the Active Tectonic Boundaries on the Chinese Mainland

Based on the research and the division of the active tectonic blocks and their boundaries on the Chinese mainland, the feature of the large earthquake activities on the 24 boundaries between the 6 active tectonic block regions (grade Ⅰ) and the 22 active tectonic blocks (grade Ⅱ) are studied. The seismicity levels on the active tectonic block boundaries are discussed considering the large earthquake frequency and the released strain energy in unit distance and time. The theoretic maximal magnitude and the recurrence period of each boundary are then calculated from the G-R relation. By comparing this with the actual earthquake records, it is found that the intensities of the earthquake deduced from the seismic activity parameter (a/b) on the main active boundaries on the Chinese mainland are consistent with that of the natural earthquakes. Meanwhile, an inverse relation is found between the recurrence periods of large earthquakes and the tectonic motion rate on the boundaries. These results show that the a, b values of each boundary obtained in this paper are valuable. In addition, the present seismic activities and hazards of these boundaries are also probed into with the historical data and their elapsed time on each boundary based on the hypothesis that the large earthquakes satisfy Poisson distribution.

Application of support vector machine to synthetic earthquake prediction

This paper introduces the method of support vector machine （SVM） into the field of synthetic earthquake prediction, which is a non-linear and complex seismogenic system. As an example, we apply this method to predict the largest annual magnitude for the North China area （30°E-42°E, 108°N-125°N） and the capital region （38°E-41.5°E, 114°N-120°N） on the basis of seismicity parameters and observed precursory data. The corresponding prediction rates for the North China area and the capital region are 64.1% and 75%, respectively, which shows that the method is feasible.

A SCR method for uncertainty estimation in geodesy non-linear error propagation: Comparisons and applications

We review three derivative-free methods developed for uncertainty estimation of non-linear error propagation, namely, MC(Monte Carlo), SUT(scaled unscented transformation), and SI(sterling interpolation). In order to avoid preset parameters like as these three methods need, we introduce a new method to uncertainty estimation for the first time, namely, SCR(spherical cubature rule), which is no need for setting parameters. By theoretical derivation, we prove that the precision of uncertainty obtained by SCR can reach second-order. We conduct four synthetic experiments, for the first two experiments, the results obtained by SCR are consistent with the other three methods with optimal setting parameters, but SCR is easier to operate than other three methods, which verifies the superiority of SCR in calculating the uncertainty. For the third experiment, real-time calculation is required, so the MC is hardly feasible. For the forth experiment, the SCR is applied to the inversion of seismic fault parameter which is a common problem in geophysics, and we study the sensitivity of surface displacements to fault parameters with errors. Our results show that the uncertainty of the surface displacements is the magnitude of ±10 mm when the fault length contains a variance of 0.01 km^(2).

Earthquake Surface Rupture Features and Tectonic Significance of the Tazang Fault in the Eastern Part of the East Kunlun Fault Zone

The East Kunlun fault zone is located in the northern margin of the Bayan Har block. The study of earthquake rupture behavior in the fault zone is of importance for understanding the future seismic risk in northwest Sichuan. A number of geological field investigations, typical micro topography DGPS measurements and sample dating show that the earthquake activity of the East Kunlun fault zone extends to the north boundary of Zoige basin, a segment known as the Luocha segment of Tazang fault. In the satellite image, the segment is seen clearly as gray and yellow strips. The earthquake deformation zone mainly features fault scarp, valleys on the slope, offset gullies and terraces, linear distribution of plants, waterfall, fault spring, fault sag pond, and landslide, collapse and talus associated with surface rupturing. These phenomena are distributed intermittently along the re-existing fault and form a ～50km-long inverse L-shaped deformation zone. Fault activities caused left-lateral offset of gullies and terraces, with horizontal displacement concentrated at 5.5m^6m, 18m～23m, 68m～75m, and 200m～220m, respectively. The recent earthquake occurred between 340±30～500±30BP. The macro epicenter is located 5km～7km northwest of Benduo village, with magnitude of MW7.3～7.4, maximum coseismic displacement of 6m, horizontal displacement 5.5m～6m and vertical displacement 0.2m～0.5m, being in a proportion of 5∶1～10∶1. These phenomena show that the Tazang fault is the causative fault of this earthquake. The fault is a Holocene active fault and was dominated recently by left-lateral movement with a small amount of thrust component under compressive shear stress. This characteristic is similar to the movement in other segments of the East Kunlun fault zone. The results of this study support the "continental escape" model.

Earthquake Activity Features Before Earthquakes with M_S≥7.0 in the Central-Northern Qinghai-Xizang(Tibet) Block

We have studied the seismicity features of M_S≥5.0 earthquakes two years before strong earthquakes with M_S≥7.0 occurred in the central-northern Qinghai-Xizang (Tibet) block since 1920. The results have showed that there is an obvious gap or quiescence of M_S5.0～6.9 earthquakes near epicenters. We have also studied statistical seismicity parameters of M_S5.0～6.9 earthquakes in the same region since 1950. The results have showed that earthquakes with M_S≥7.0 occurred when earthquake frequency is relatively high and earthquake time, space accumulation degrees are rising. And the prediction effect R value scores are between 0.4～0.7. We have concluded that, before earthquakes with M_S≥7.0 in the central-northern Qinghai-Xizang (Tibet) block, M_S5.0～6.0 earthquake activity in the whole area increased and accumulated in time and space, but earthquakes with M_S≥7.0 occurred where M_S5.0～6.0 earthquake activity was relatively quiet.

The space and time distribution characteristics of the shear stress field for the sequence of the Wuding earthquake

Follow Chen and Duda's model of spectral fall-off of ω~3, the dependence of peak parameters of ground motion, peak displacement d_m, peak velocity vin and peak acceleration a_m, upon the environment stress τ_o-values are studied using near source seismic digital recordings for the sequence of the Wuding, Yunnan, M = 6.5 earthquake, in which, as a new thought, the peak parameters are assumed to be related to the medium Q-value. Three formulae for estimating the environment stress τ_o-values by the peak parameters of three types of ground motions are derived. Using these formulae, the environment stress τ_o-values are calculated for the sequence of the Wuding earthquake. The result show that τ_o-values calculated by the three formulae are constant largely, the averages of τ_o are in the range of 5.0-35 MPa for most earthquakes. It belongs to the high-stress earthquakes sequence: the high-stress values are restricted to the relatively small area closely near to the epicenter of the main shock. The fine distribu tion structure for the contours of the environment stress τ_o-values is related closely to the strong aftershocks. The analysis of spatial and temporal feature of To-values suggests that the earthquakes sequence in a rupture process generated at the specific intersection zone of seismo-tectonics under high-stress background.

Seismic response of precast reinforced concrete wall subjected to cyclic in-plane and constant out-of-plane loading

This paper provides insight into the seismic behavior of a full-scale precast reinforced concrete wall under in-plane cyclic loading combined with out-of-plane loading replicated by sand backfill to simulate the actual condition of basement walls.The tested wall exhibited flexural cracks,owing to the high aspect ratio and considerable out-of-plane movement due to lateral pressure from the backfill.The wall performed satisfactorily by exhibiting competent seismic parameters and deformation characteristics governed by its ductile response in the nonlinear phase during the test with smaller residual drift.Numerical analysis was conducted to validate experimental findings,which complied with each other.The numerical model was used to conduct parametric studies to study the effect of backfill density and aspect ratio on seismic response of the proposed precast wall system.The in-plane capacity of walls reduced,while deformation characteristics were unaffected by the increase in backfill density.An increase in aspect ratio leads to a reduction in in-plane capacity and an increase in drift.Curves between the ratio of in-plane yield capacity and design shear load of walls are proposed for the backfill density,which may be adopted to determine the in-plane yield capacity of the basement walls based on their design shear.