Quantitative data about active tectonics and possible locations of strong earthquakes in the future in the northwestern Beijing

Deterministic, probabilistic and composite-grading methods are used to get the possible locations of strong earth-quakes in the future in Norwest Beijing and its vicinity based on the quantitative data and their accuracy about active tectonics in the research area and by ordering, some questions in the results are also discussed. It shows that the most dangerous fault segments for strong earthquakes in the future include: segments B and A of the southern boundary fault of the Yangyuan basin, the southern boundary fault of the Xuanhua basin, the east segment of the southern Huaian fault and the east segment of the northern YanggaoTianzhen fault. The most dangerous area is YangyuanShenjing basin, the second one is TianzhenHuaianXuanhua basin and the third dangerous areas are WanquanZhangjiakou and northeast of Yuxian to southwest of Fanshan.

Parameter estimation of the stochastic AMR model and its application to the study of several strong earthquakes

Based on the stochastic AMR model, this paper constructs man-made earthquake catalogues to investigate the property of parameter estimation of the model. Then the stochastic AMR model is applied to the study of several strong earthquakes in China and New Zealand. Akaikes AIC criterion is used to discriminate whether an accelerating mode of earthquake activity precedes those events or not. Finally, regional accelerating seismic activity and possible prediction approach for future strong earthquakes are discussed.

Relationship between the earthquake sequences of Tangshan and Xingtai and the three dimensional velocity structure──Discussion on predicting strong earthquakes of swarm-type

In this paper, based on the results of tomographic image of Tangshan and Xingtai areas, the relations between thecharacteristics of the two strong earthquake sequences and their three-dimensional velocity structures are studied.The research results indicate that:① Mosaic distribution of low-velocity bodies and high-velocity bodies, especially the existence of high-velocity bodies with large size in crust are the common basis of development of thetwo earthquake sequences. ② Scale, depth, and heterogeneity of high-velocity and low-velocity bodies are theimportant factors to effect the characteristic of earthquake sequences. ③ The depth of the high-velocity body inTangshan area is less than that in Xingtai area, which is the principal reason why the dominant focal depth and thebiggest focal depth of Tangshan earthquake sequence are less than Xingtai's. ④ The depth of the high-velocitybodies in Ninghe area is more than that in Tangshan-Luanxian area, which lead to the biggest magnitude and epicentral intensity are lower. These results could be helpful for predicting the main shock of strong swarm-typeearthquakes and later strong aftershocks.

Spatio-temporal characteristics of strong aftershocks of the M_S8.0 Wenchuan earthquake

Based on Gutenberg-Richter＇s relation,Bath＇s law,Omori＇s law and Well＇s relation of rupture scale,this paper forecasts the temporal decay,total number,possible area and greatest magnitude of strong aftershocks（greater than or equal to M6.0） of the MS8.0 Wenchuan earthquake by using the magnitude and statistical parameters of earthquakes in California area of USA.The number of strong aftershocks,the parameters of Gutenberg-Richter＇s relation and the modified form of Omori＇s law are validated based on the relocation data of aftershock sequence of the MS8.0 Wenchuan earthquake.Moreover,the spatio-temporal characteristics and wave energy release of the strong aftershocks（M≥6.0） are analyzed.The result shows that strong aftershocks may occur at the end of local drop and sharp drop on the wave energy release curve.

Analysis on the master event method and precise location of 1997 Jiashi strong earthquake swarm in western China

Master event location method was described in detail in this paper. Some problems in the application of master event method have been analyzed and some improvements of the method have been made. As compared the location results of MS>=3.0 earthquakes of Jiashi swarm obtained by using this method with that by the traditional absolute method, the result obtained by using the master event method shows more reasonable and more consistent with that from the focal mechanism solutions. After relocation, we can see, the epicenters of M>=5.0 earthquakes show an echelon-type alignment along NNW-SSE direction, and all earthquakes concentrate nearly in a volume region about 30 km (N-S) × 15 km (E-W) × 15 km (U-D). Earthquake focal depths are mainly in the range of 15-28 km.

Preliminary results of strong ground motion simulation for the Lushan earthquake of 20 April 2013,China

The earthquake occurred in Lushan County on 20 April, 2013 caused heavy casualty and economic loss. In order to understand how the seismic energy propagates during this earthquake and how it causes the seismic haz- ard, we simulated the strong ground motions from a rep- resentative kinematic source model by Zhang et al. （Chin J Geophys 56（4）：1408-1411, 2013） for this earthquake. To include the topographic effects, we used the curved grids finite difference method by Zhang and Chen （Geophys J Int 167（1）：337-353, 2006）, Zhang et al. （Geophys J Int 190（1）：358-378, 2012） to implement the simulations. Our results indicated that the majority of seismic energy con- centrated in the epicentral area and the vicinal Sichuan Basin, causing the XI and VII degree intensity. Due to the strong topographic effects of the mountain, the seismic intensity in the border area across the northeastern of Boxing County to the Lushan County also reached IX degree. Moreover, the strong influence of topography caused the amplifications of ground shaking at the moun- tain ridge, which is easy to cause landslides. These results are quite similar to those observed in the Wenchuan earthquake of 2008 occurred also in a strong topographic mountain area.

Segmentations of active normal dip-slip faults around Ordos block according to their surface ruptures in historical strong earthquakes

From the results of researches of active faults in resent years, a correlation analysis between segments of the faults according to surface ruptures in nine historical strong earthquakes occurring in downfaulted system and active structures around Ordos block is conducted in paper. The result shows that there is a good correlation between them, except few individual data that have more uncertain parameters. It shows that intensity and segments of surface ruptures in these strong earthquakes are intrinsically related with the active structures. These strong earthquakes produced stable and unstable rupture boundaries of characteristic-earthquake type and successive occurrence of strong earthquakes on the different boundary faults in the same tectonic unit.

Analysis of landslide damage caused by the 2008 Wenchuan earthquake using strong motion data: A case study in the Beichuan county town

The county town of Beichuan county, China, experienced catastrophic destruction due to landslides induce by the 2008 Wenchuan earthquake. In consideration of the special location of the county town, this paper selected the landslides induced in the town as representative of large-scale near-rupture landslides, and quantitatively analyzed why the landslide damage was so destructive in the town by using strong motion data obtained from the Wenchuan earthquake in the Longmenshan area. Three methods were employed to estimate the landslide damage using strong motion data. （1） Peak ground accelerations （PGAs） on the hanging wall were used to evaluate the PGAs on the landslide sites in the town. The evaluated average PGAs were all greater than I g, indicating that the ground motion intensity was very strong during the earthquake. （2） Acceleration time histories, from another station with similar geological conditions to the town, were used to evaluate the critical acceleration changing range, and the estimated values showed the geological conditions were very susceptible to earthquakes. （3） Acceleration time histories, from two stations on the hanging and foot walls of the rupture, and near the town, were used to calculate the Newmark displacements, and all the evaluated displacements indicated that landslides were very likely. The results show that the slopes, susceptible to earthquakes in the Beichuan county town, were easily triggered under such strong ground-motion intensity and developed into large-scale catastrophic events.

Grouping occurrences being the fundamental feature of the strong earthquakes in Chinese mainland

The temporal and spatial distributions of all the 259 M≥6 earthquakes of eastern Chinese mainland (λ≥108° E) and its adjacent area and all the 153 M≥7 earthquakes of western Chinese mainland (λ<108°E) and its adjacent area up to 1991 were analyzed systematically.These earthquakes are called as strong earthquakes and those of the east before and after 1600,and those of the west before and after 1900, are called respectively as former ones and latter ones.Most of these events were divided into 45 sets of which the each relatively concentrated in both time and space and took the form of group.In the grouping form,the probability of occurrence of a strong earthquake higher than the average appeared simultaneously in time and space.The grouping occurrences of the strong earthquakes of Chinese mainland has been determined as a fundamental feature of the seismicity.

Preliminary analysis for the roles of crustal low-velocity and high-conductivity body in process of strong earthquake preparation

In this paper, the roles of low velocity and high conductivity body inside the crust in the process of strong earth quake preparation are approached by using theoretical analysis method based on the comprehensive researches on the fine structure of strong seismic source in the North China. The following results are obtained. The low-velocity and high-conductivity body plays the promoting role for the action of deep-seated structure in the medium stage of earthquake preparation, except that its existence is advantageous to the stress concentrating in the overlying brittle layer during the process of earthquake preparation. And it plays the triggering role for the occurrence of strong earthquake in the later stage of earthquake preparation.

Tomographic determination of the upper crustal structure in the Jiashi strong earthquake swarm region

A three-dimensional temporary seismic transmission array was arranged in a 50x60 km2 region around Jiashi strong earthquake swarm to receive seismic waves generated by 8 fires from different azimuths. With the inversion method without model blocks and using P and S reflections from Moho at critical distances, the 3-D images of P, S velocity perturbation and ratio vP/vS perturbation of the upper crust under the seismic array were reconstructed. Meanwhile, the seismicity of the Jiashi earthquake swarm was taken into consideration in the analysis of the seismogenesis. The results indicate that the upper crustal structure under the Jiashi strong earthquake swarm region is characterized by significant inhomogeneity both laterally and vertically. From 12 km depth, it is clear that there is an NNW-oriented high P-wave velocity anomalous body corresponding to the epicenter of the swarm with low-velocity anomaly around it, which is the direct cause of the strong earthquakes. High vP/vS is distributed in the same location, which may indicate the decline of shear strength of the source region owing to relative softness of the medium, this can be accounted as an explanation for the seismicity feature of the Jiashi strong earthquake swarm.

The characteristics of variation in inhomo geneity of temporalspatial distribution of short to imminent precursors before strong earthquakes

C_v is used in this paper to describe the variation in inhomogeneity of spatial and temporal distribution of precur sors. The inhomogeneous variation in the spatial and temporal distribution of the anomalies in water radon and electromagnetic waves before M_s≈6 earthquakes in northern North China is analyzed in detail. Results show that before a moderate to strong earthquake, the distribution of anomalies in water radon and electromagnetic waves changes inhomogeneously, i.e., C_v increases significantly. The inhomogeneity in spatial distribution of short-to- imminent precursors increases before a strong earthquake, which may relates to the enhancement of crustal strain field. The research will not only help us to know more about the process of seismogeny and to improve practical earthquake prediction, but also blaze a new way to do earthquake prediction with present precursor data.

Study of the Seismicity of Strong Earthquakes in the Yunnan Area

Yunnan is located in the east margin of the collision zone between the India Plate and the Eurasian Plate on the Chinese Continent, where crustal movement is violent and moderatestrong earthquakes are frequent. In addition, the area features marked active block movement. Therefore, Yunnan is a perfect place for research on strong earthquake activity. Through the study on the temporal and spatial distribution of the M ≥ 6.7 earthquakes and the related earthquake dynamics in Yunnan in the last century, we conclude that the four seismically active periods, which are characterized by alternative activity in the east and the west part of Yunnan, possibly result from a combination of active and quiescent periods in each of the east and west part. And for every 100 years, there may be a period in which strong earthquakes occur in the east and west parts simultaneously. In addition, the seismicity of strong earthquakes in Yunnan corresponds well to that in the peripheral region. The seismicity of the great earthquakes in the Andaman-Myanmar Tectonic Arc belt indicates, to some extent, the beginning of a seismically active period in Yunnan. The seismicity of strong earthquakes in east Yunnan is closely related to that in Sichuan. Strong earthquakes in Sichuan often occur later than those in Yunnan. Furthermore, in the east part of Ynnnan, the three procedures including continuous occurrence of moderate-strong earthquake, quiescent period, and the occurrence of the first strong earthquake may be the style of the beginning of the earthquake active period. The above cognition is helpful to the study of earthquake prediction, seismogenic mechanism, and the dynamics of the plate margin in Yunnan.

The Characteristics of Time Series of Strong Earthquakes in the World and the Chinese Mainland

Based on the strong earthquake catalogue, this paper discusses the characteristics of the time series of strong earthquake activities in the world, western Chinese mainland and its peripheral ＂big triangle seismic region＂, as well as the Chinese mainland. According to the analysis of the periodic features of global seismicity of M I〉 8. 0 strong events, it is found that there is significant difference in global seismicity before and after the 1960s. Statistical analysis with the Fisher method has revealed that the ＂big triangular seismic region＂ has experienced a process of M8.0 earthquake activity with a duration of over a hundred years since 1800. Further analysis shows that the global seismicity and the ＂big triangular seismic region＂ possibly has a period of a hundred-year scale, and has quasi- synchronicity to a certain extent. The shallow earthquake activity of Ms I〉 7. 0 in the Chinese mainland is obviously controlled by the seismicity in the big triangular seismic region and by global seismicity in a larger spatial-scale. In terms of the time series of these earthquakes, the seismicity shows a decadal and century-scale activity patterns.

Periodic spectral characteristics of seismicity before strong earthquakes and their application

Periodic spectral characteristics of earthquake activity in the seismic strengthening areas of 24 ewthquakes withM≥ 6.0 are studied by the maximum entropy spectral method whose superiority is tested. Then the follow resultshave been obtained : ① The periodic spectra of seismic activity in seismic strengthening areas are different indifferent stage in earthquake-generating processes. Long periodic spectra and short ones coexist in normal stage,while only short ones (on average, 43% of long ones) exist and long ones disappear prior to ear’thquakes. ② Theappearing time of short period before earthquakes has some relations with magnitude. The result shows thatdecades or even one hundred years is the common value for a great earthquake of M=8.0, 30 years for one withmagnitude about 7 and 20-30 years for a strong quake of M=6.0. For the same magnitude earthquakes in differentregions the appearing time is also different. For example, it is longer in North China than that in the western pan ofChina. Then the characteristics are preliminarily explained applying the strong body earthquake-generating model.Applying the maximum entropy spectral method, the idea of tendency prediction for strong and great earthquakesis suggested and used into practice. for example. the tendency predictions of the Wuding earthquake with M=6.5and the Lijiang earthquake of M=7.0 in Yunnan Province got some positive effects. So a new method of tendencyprediction of M≥6.0 earthquakes is offered.

An Inhomogeneous Distribution Model of Strong Earthquakes along Strike-Slip Act ive Fault Segments on the Chinese Continent and Its Implication in Engineering Seismology

Through the statistical analysis of earthquake distribution along 51 strike-sli p active fault segments on the Chinese continent, we found that strong earthquak e distribution along the seismogenic fault segments is inhomogeneous and the dis tribution probability density p(K) can be stated as p(K)=1.1206e -3.947K in which K=S/(L/2), S refers to the distance from earthquake epicenter to the center of a fault segment, L is the length of the fault segment. The above model can be utilized to modify the probability density of earthquake occurrence of t he maximum magnitude interval in a potential earthquake source. Nevertheless, it is only suitable for those potential earthquake sources delineated along a sing le seismogenic fault. This inhomogeneous model has certain effects on seismic risk assessment, especia ll y for those potential earthquake sources with higher earthquake reoccurrence rat es of the maximum magnitude interval. In general, higher reoccurrence rate of th e maximum magnitude interval and lower exceeding probability level may bring lar ger difference of the results in seismic risk analysis by adopting the inhomogen eous model, the PGA values increase inner the potential earthquake source, but r educe near the vicinity and out of the potential earthquake source. Taking the T angyin potential earthquake source as an example, with exceeding probability of 10% and 2% in 50 years, the difference of the PGA values between inhomogeneous m odel and homogenous models can reach 12%.

The Statistical Analysis of Migration of Strong Earthquakes─Taking the North China Region as an Example

The migration of strong earthquakes is an important research topic because the migration phenomena reflect partly the seismic mechanism and involve the prediction of tendency of seismic activity. Research on migration of strong earthquakes has mostly focused on finding the phenomena. Some attempts on getting regularity were comparatively subjective. This paper suggests that there should be indices of migration in earthquake dataset and the indexes should have statistical meaning if there is regularity in the migration of strong earthquakes. In this study, three derivative attributes of migration, i.e., migration orientation, migration distance and migration time interval, were statistically analyzed. Results in the North China region show that the migration of strong earthquakes has statistical meaning. There is a dominant migration orientation (W by S to E by N), a dominant distance (≤100km and on the confines of 300～700km), and a dominant time interval (≤1a and on the confines of 3～4a). The results also show that the migration will differ slightly with different magnitude range or earthquake activity phase.

Anomalies of Precursory Group and Grouped Strong Earthquakes in the Sichuan-Yunnan Region

Three methods of extracting the information of anomalies of a precursory group are put forward, i.e., the mathematical analyses of the synthetic information of earthquake precursors (S), the inhomogeneous degree of precursory groups (ID) and the values of short-term and impending anomaly in near-source area (NS). Using these methods, we calculate the observational data of deformation, underground fluid and hydrochemical constituents obtained from different seismic stations in the Sichuan-Yunnan region and conclude that the synthetic precursory anomalies of a single strong earthquake with M S6.0 differ greatly from those of the grouped strong earthquakes, for the anomalous information of precursory groups are more abundant. The three methods of extracting the synthetic precursory anomaly and the related numerical results can be applied into the practice of prediction to the grouped strong earthquakes in the Sichuan-Yunnan region. Inhomogeneous degree (ID) of synthetic precursory anomaly can be identified automatically because it takes the threshold of distributive characteristics of the anomalies of precursory group as its criterion for anomaly.

Parameter estimation of the stochastic AMR model and its application to the study of several strong earthquakes

Based on the stochastic AMR model, this paper constructs man-made earthquake catalogues to investigate the property of parameter estimation of the model. Then the stochastic AMR model is applied to the study of several strong earthquakes in China and New Zealand. Akaikes AIC criterion is used to discriminate whether an accelerating mode of earthquake activity precedes those events or not. Finally, regional accelerating seismic activity and possible prediction approach for future strong earthquakes are discussed.

Research on the Characteristics and Repeatability of Strong Earthquake Activity in Sichuan-Yunnan

According to the method for predicting strong earthquakes using seismicity patterns,this paper summarizes the seismicity anomalies, generally called anomalous seismicity patterns,as the basis for prediction based on some historical data in the Sichuan-Yunnan seismic zone. Using our results,it can be confirmed that these anomaly patterns,which reflect the features of the late stage of strong earthquake preparation process and stress release in the main shock rupture zone,did exist before many earthquake cases. This paper also introduced the characteristics of seismic repeatability and its validation result,and discussed the mechanism of repeatability,which will have an application value for strong earthquake tendency prediction.