Precursory Seismic Quiescence Before July 28, 1976 Great Tangshan,China, Earthquake

The earthquake catalog with the minimum completeness magnitude of ML=1.7 during the period from 1970 to 1976 has been used as basic data for the research on seismic quiescence in source area before occurrence of the July 1976 great Tangshan earthquake in China,based on the analyses of the detectability of seismic network,and of relation between earthquake magnitude and frequency in Northern China.The temporal processes of seismicity rate(January 1970-July 1976)before the July 1976 great Tangshan earthquake for four researched sub regions in and around source area(aftershock area)of the mainshock are investigated and compared.It is found that there exist abnormal seismic quiescence with duration of 38 months in the subregion located in western part of aftershock area,which is significant statistically at confidence level of 0.99 and larger by beta-test.In addition,because there were no false alarms except for the above abnormal interval in the west aftershock area,and the Tangshan mainshock and 85% of af     

Discussion on the Seismogenic Fault of the 1976 Tangshan Earthquake

The opinions of two papers carried in the journal "Seismology and Geology" are discussed in the paper.One is that the Tangshan fault is a high-angle,west-dipping and thrust with strike-slip fault.The other is that the Fuzhuang-Xihe fault distributed on the east side of Tangshan city is the seismogenic fault that caused the Tangshan earthquake.For the former opinion,it needs to explain the relationship between the active style of the thrust Tangshan fault and the formation genesis of a Quaternary depression along the west side of Tangshan city.For the latter opinion,if the Fuzhuang-Xihe fault is the seismogenic fault of the Tangshan earthquake,it needs to explain the genesis relationship between this west-dip slip fault zone and the strike-slip surface fissure zone that extends through Tangshan city.And it needs more evidence exclude the possibility that the surface rupture belongs to the rupturing of a secondary structure.This paper suggests doing more work on the active fault that controls the Caobo Quaternary depression.     

On Shear-wave Splitting in Tangshan Region

Shear-wave splitting in Tangshan region is studied by using digital seismic data.Analyzing 3-component digital seismic data in Tangshan strong ground motion array,it is found that almost all earthquakes occurred during 1982 to 1984 have significant shear-wave splitting.The polarization directions of faster shear waves in 7 stations are near EW,which are consistent with the axis of maximum principal compressive stress obtained from earthquake fault mechanisms and geodetic surveys.The crack densities of the 7 stations are roughly estimated,0.019 for TS01,TS02 and TS15,0.015 for TS03,TS07 and TS18 and 0.024 for TS19,by using the average time delay of slow shear-wave at the 7 stations.     

Relationship between the earthquake sequences of Tangshan and Xingtai and the three dimensional velocity structure

In this paper, based on the results of tomographic image of Tangshan and Xingtai areas, the relations between the characteristics 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 the two earthquake sequences. ②Scale, depth, and heterogeneity of high-velocity and low-velocity bodies are the important factors to effect the characteristic of earthquake sequences.③ The depth of the high-velocity body in Tangshan area is less than that in Xingtai area, which is the principal reason why the dominant focal depth and the biggest focal depth of Tangshan earthquake sequence are less than Xingtai's.④The depth of the high-velocity bodies 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-type earthquakes and later strong aftershocks.     

Homo erectus pekinensis''''s age and environment——with discussion on the relationship among Homo erectus from Beijing,Nanjing and Chenjiawo

This paper inspects the relationship between Homo erectus from Beijing, Nanjing and Chenjiawo on the viewpoint of environmental variations. Pieces of evidence show that Nanjing and Chenjiawo Homo erectus lived in glacial age at the Marine Oxygen Isotope Stage (MIS) 16, while Homo erectus pekinensis in major interglacial age at MISs 15-13. It is also recovered that the cave deposits in Tangshan, Nanjing, and Zhoukoudian, Beijing, as well as the deposits at the Homo erectus site in Chenjiawo, have undergone some similar development process. All of them originated from early-middle Middle Pleistocene, and have gone through the test of the major glacial age at MIS 16 and the major interglacial period at the paleosol stage S5. At the same time, they were also closely connected with some environment events, such as the uplift of the Qinghai-Xizang Plateau, the formation of glaciations and the loess accumulations.     

Temporal vP/vS variation characteristics in different zones of China’s Capital Circle area before and after Wen’an earthquake

On July 4, 2006, an earthquake of MS5.1 took place in Wen’an, Hebei Province, just at the south center of China’s Capital Circle area digital seismograph network. It is the strongest event recorded ever since the network went into operation in 2002. We processed the vast amounts of phase data yielded by the 107 digital seismic stations between 2002~2007 using Wadati method. In order to improve the precision and stability of shear and compressional wave velocities (vP/vS) calculation, we impose a number of restrictions on the computation environment and condition, e.g., the earthquakes are densely concentrated, selected stations are limited in range, the number of stations in- volved in the computation is larger than 5 and linear fitting features high precision and small error. Under these restrictions, the study shows that vP/vS in and around Wen’an and Tangshan underwent a normal-low-normal proc- ess one year before Wen’an earthquake, vP/vS became obviously low and the low ratio lasted for about one year, meanwhile, little variation of vP/vS was seen in Xingtai, northwest of Beijing, southwest of Beijing, Beijing-Tianjin and Beijing; after the quake, the vP/vS returned normal in Wen’an and Tangshan. Error and stability analysis of the calculated result for vP/vS shows it is convincible that anomaly appeared in and around Wen’an and Tangshan be- fore Wen’an earthquake.     

THE VERTICAL DEFORMATION BEFORE AND AFTER THE TANGSHAN EARTHQUAKE OF 1976

Based on the data of 18 times of leveling carried out during 1954 to 1985, the relative stability degrees of relevelling nodes in the Tangshan area are calculated. According to these results, the characteristics of crustal vertical deformation before and after the Tangshan Earthquake(28/7/1976,Ms =7.8) are studied. Our study indicates that probably since 1968 significant relative movements between structural blocks in that area had appeared and continued till 1978. The seismic fault wa     

Numerical simulation of dynamic process of the Tangshan earthquake

In this paper, the new LDDA (Lagrangian Discontinuous Deformation Analysis) method is used in modeling the dynamic process of the MS=7.8 Tangshan earthquake on July 28, 1976 and obtain directly the dynamic and quasi-static dislocations, shear stress drops, fracture velocities of the Tangshan earthquake fault. The simulation shows that the slip history at each point of the fault is different. The displacement vectors at the concave side of the fault is greater than that of the convex side of the fault. The "over shoot" of the fault slip is greatest at the middle part of the fault and attenuates to its ends. The rupture velocities of the fault from the epicenter towards south-west and towards north-east are 3.08 m/s and 1.18 m/s, respectively, the average one is 2.13 m/s. The maximum dynamic and quasi-static dislocations are 7.1 m and 6.2 m respectively, the average quasi-static one on the fault is 4.5 m. The maximum dynamic and quasi-static shear stress drops are 8.1 MPa and 5.4 MPa, respectively, the average quasi-static shear stress drop is 3.9 MPa.We found that the rupture velocities and shear stress are related to the initial stress states of the fault.     

The Spatial and Temporal Variatiion of Modern Tectonic Stress Field in North CHina before and after the 1976 Tangshan Earthquake

By using 126 earthquake focal mechanism solutions (M S≥4.7) during the period of 1963～1998, modern tectonic stress field in North China is inverted by means of the step by step convergence. The inversion results indicate that the tectonic stress field in the research region is clearly variational in space and time: (1) The middling principal stress axis σ 2 is basically vertical. The maximum and minimum principal stress axes σ 1 and σ 2 are nearly horizontal, but the azimuths of σ 1 and σ 3 are inconsistent in different districts and periods. (2) Before the Tangshan earthquake in 1976, the three principal stress axes are uniform. The azimuth of maximum principal stress axis σ 1 is 68° (striking in a NEE-SWW direction). (3) After the Tangshan earthquake, the maximum principal stress axis σ 1 and minimum principal stress axis σ 3 have variations in different districts. In the northern area of North China and on the eastern side of the Tancheng-Lujiang fault zone, the maximum principal stress axis σ 1 is also striking in a NEE-SWW direction. Its azimuth is 68°. It is the same as that before the Tangshan earthquake. In the southern area of North China, the maximum principal stress axis σ 1 is striking in a E-W direction and its azimuth is 87°.     

Temporal and spatial variation characteristics of present stress field in the northern area of North China

From focal mechanism solutions of the earthquakes in the northern part of North China during the period of 2002～2006,the directions of principal stress axes in 4 stress sub-districts are analyzed using a grid test method.The characteristic of present crustal stress directions is discussed.Based on this result and on the focal mechanism solutions calculated for some events in the period of 1977～1998,in combination with some other study results,the temporal variation of present crustal stress directions in the northern part of North China is investigated.The re-sults confirm that the direction of crustal principal stress in some regions had somewhat rotated after the 1976 Tangshan M7.8 earthquake.The mean P axes of the focal mechanism solutions rotated clockwise not only in Tangshan sub-district,but also in Beijing and Xingtai sub-districts after the Tangshan earthquake.In Beijing and Xingtai sub-districts the orientations of principal stress axes in the period of 2002～2006 are consistent with that before the Tangshan earthquake,implying that the stress orientations has rotated back to the state before the Tang-shan earthquake in these two sub-districts.The directions of the mean P axes are nearly E-W in Tangshan sub-dis-trict since the M7.8 earthquake.The present stress field in the sub-district northwest to Beijing,or in the western part of the Zhangjiakou-Bohai fault zone,is relatively stable during the time period concerned in this study.Because of the limitation of data,this paper only states a possible variation of stress field in the northern part of North China in the recent decades.     

DILATION-CREEP MODEL OF EARTHQUAKE SOURCE DEVELOPMENT AND THE TANGSHAN EARTHQUAKE

The article has made a simple exposition of the dilation-creep modelof earthquake source development(abbreviated DC).Inelastic volumetricdilation of rock masses and fault creep are considered as two basic phys-ical processes in the DC model.The physical mechanism of precursors ofthe M=7.8 Tangshan earthquake has also been analysed and discussed inthis paper.The results show that the precursors of the Tangshan earth-quake were not caused by only one factor and the precursors observed in-and around the epicentral area prior to this earthquake can be grouped into three types.TypeⅠprecursors may be causally related to rock dilata-ncy.TypeⅡprecursors result from fault creep.TypeⅢprecursors maybe associated with some sort of upward migration of mass in the crust orthe upper mantle,and/or may be attributed to large scale stressing processaccommodated by some combination of stable slippage and discontinuousbrittle rupture(namely small earthquake)along the faults.It was sug-gested that repeated dilation and discontinuous creep occurred during theprocess of source development of the Tangshan earthquake and the prepa-ratory process of the Tangshan earthquake can be divided into the follo-wing six phases:elastic stress accumulation(from 1954 to 1967);earlyinelastic dilation(from 1968 to 1969);early fault creep(from 1970 to1973);the second dilation(from the end of 1973 to the first half of 1975);the second evident fault creep(from the second half of 1975 to the end ofApr.1976);and fault creep just before the main shock(from the end ofApr.1976 to the occurrence of the Tangshan earthquake).It is regardedhat the preparatory process of the Tangshan earthquake,as one of the intraplate events,may be controlled jointly by the upward migration ofdeep mass and large scale intraplate stress field.This characteristic prob-ably is different from that of earthquake along plate boundary.     

Multifractal characteristics of general stress release（GSR）of earthquakes

Using multifractal spectrum estimating method based on the wavelet,the multifractal characteristics of GSR of earthquakes in China,Japan and New Zealand regions have been studied.It is shown that the multifractal spectra of GSR are obviously different in inter-and intra-plate regions.Moreover,though Japan and New ZeaIand are all located at the boundary of plates,West and East China are all characterized of continental tectonic structure,the multifractal spectra of GSR for both the two regions are also different.Further analysis shows that the natures of multifractal spectra of GSR are somehow related to the complexity of tectonics.     

Visco-elastic stress triggering model of Tangshan earthquake sequence

We calculated the Coulomb failure stress change generated by the 1976 Tangshan earthquake that is projected onto the fault planes and slip directions of large subsequent aftershocks.Results of previous studies on the seismic fail-ure distribution,crustal velocity and viscosity structures of the Tangshan earthquake are used as model constraints.Effects of the local pore fluid pressure and impact of soft medium near the fault are also considered.Our result shows that the subsequent Luanxian and Ninghe earthquakes occurred in the regions with a positive Coulomb fail-ure stress produced by the Tangshan earthquake.To study the triggering effect of the Tangshan,Luanxian,and Ninghe earthquakes on the follow-up small earthquakes,we first evaluate the possible focal mechanisms of small earthquakes according to the regional stress field and co-seismic slip distributions derived from previous studies,assuming the amplitude of regional tectonic stress as 10 MPa.By projecting the stress changes generated by the above three earthquakes onto the possible fault planes and slip directions of small earthquakes,we find that the "butterfly" distribution pattern of increased Coulomb failure stress is consistent with the spatial distribution of follow-up earthquakes,and 95% of the aftershocks occurred in regions where Coulomb failure stresses increase,indicating that the former large earthquakes modulated occurrences of follow-up earthquakes in the Tangshan earthquake sequence.This result has some significance in rapid assessment of aftershock hazard after a large earthquake.If detailed failure distribution,seismogenic fault in the focal area and their slip features can be rapidly determined after a large earthquake,our algorithm can be used to predict the locations of large aftershocks.     

A new model on the cause of Tangshan earthquakes in 1976

Introduction The Tangshan earthquake sequence in 1976 is one of most important events in North China. Although nearly thirty years passed and there are some researches on its cause, it is far from the end. Here we introduce two explanations for the cause of Tangshan earthquakes and point out their defects. One is that there is a diamond block in NEE direction in Tangshan region, which is shaped by cutting action of NingheChangli fault, FengtaiYejituo fault, Luanxian fault and Jiyunhe fau…     

ew Breakthrough in Research of Framework and Faults in Basement of Turfan Sag

The deep information of the Turfan sag was extracted and analyzed through the re-processing of the magneto-gravitational data of the Turfan sag in the Turfan-Hami basin. It is considered that the basement faults have played an important role in the controlling of the framework, lithology and the distribution of volcanic rocks in the basement of the Turfan sag. The deep crystalline basement and the upper Hercynian folded basement were studied part by part in the sag through the combined data of aeromagnetic and electric methods. It is revealed that the Huoyanshan fault is steep in the upper and lower parts but gentle in the middle, displaying a “S” type texture, and discovered that there are at least a row of local structures in the down-thrown block of the Huoyanshan fault, through the CEMP prospecting in Huoyanshan. The result is very important for the studying of the Turfan sag as a whole.     

Lateral Inhomogeneity of Basement Layer in Three Gorges Region of Changjiang River (Yangtze River)

Seismic tomography from the Pg wave data along the non-longitudinal profile in the Three Gorges Region is presented in this paper.The seismic tomography method,and the acquisition and analysis of seismic travel time are broadly outlined.The tomography of basement reveals a great amount of significant information and shows that the low-velocity zone is due to the lithologic difference and the fault fracture zone.It also demonstrates that there exist three high-velocity zones with v>6.4 km/s at the basement; the largest of zones which strikes north-south is located at the southwestern side of Huangling Anticlinorium and extends into the anticlinorium northward.The other two high-velocity zones are,respectively,situated at the eastern side of the anticlinorium and the western side of the profile.The high-velocity zones are inferred to originate from the upwelling of material with high-velocity from deep crust.     

Synthetically adaptive robust filtering for satellite orbit determination

The precise orbit information is the premise of the application of satellite, and the precise orbit deter- mination includes dynamic and geometric methods. The dynamic method estimates the position and veloc-ity of a satellite at one epoch by extending the obser-vational arc in order to include more observations of different epochs in it. It is realized by integrating the dynamic equation of the satellite so that the observa-tions at different epochs are related to the particular state. The dy…     

Experimental study on scour and flow field in a scour hole around a T-shape spur dike in a 90° bend

In this paper results of experimental study on scour and flow field around a T-shape spur dike in a 90 degree channel bend are presented. Experiments were conducted in a laboratory channel to measure the variations of bed topography under a clear water condition. The three dimensional flow field was measured by an Acoustic Doppler Velocimeter in a scour hole due to a T-shape spur dike. It was found that by increasing the Froude number and length of spur dike the amount of scour increases. Increasing the wing length of spur dike decreases the scour. The amount of scour at the upstream of spur dike is much more as compare to that at the downstream of spur dike. By increasing the wing length of spur dike the zone of flow separation expands. As a result the sizes of vortex increase. Details of flow field are also addressed in the paper.     

Preliminary Study on the Dynamic Variations of the Surface Thermal Flux before and after the M_S5.7 Earthquake of 2005 in Jiujiang City,Jiangxi Province

The temporal and spatial variations of surface latent heat flux （SLHF） and diagnostic air temperature at 2m before and after the Ms5.7 earthquake occurring on November 26, 2005 in the area between Ruichang City and Jiujiang City, Jiangxi Province are summarized in this paper. It is found that before the earthquake significant SLHF anomalies and air temperature anomalies occurred in the epicentral area and its vicinity. The air temperature anomalies appeared from the 2nd to the 13th of November, 2005 and were concentrated at the epicentral area and in its southern part. Then two days later, that is, from the 4th to the 15th of November 2005, significant SLHF anomalies occurred in the epicentral area and to its northern area where many lakes are distributed along the active faults. During the anomalous period, the SLHF and air temperature at 2m exceeded the sum of average daily value over 26 years and 1.5 times of its mean square deviation. Both anomalies had maintained for 12 days with a peculiar distribution related to the tectonic active zone. It is considered that both of air temperature anomalies and SLHF anomalies are correlated to the movement of thermal flux from underground prior to earthquake. SLHF anomalies occurred over wide regions covered with abundant water, whereas air temperature anomalies occurred over land.     

Numerical simulation for 1975 Haicheng and 1999 Xiuyan earthquake processes by DDA+FEM

Introduction The Xiuyan earthquake(MS=5.4)on Nov.29,1999,occurred between Hushan town and Pi-anling town at the southeast end of the aftershocks of Haicheng earthquake(MS=7.3).These two earthquakes′sequences are highly similar in the way that the foreshocks are very frequent,focal mechanisms of the main shocks are about the same and fault strikes are approximately in the same direction.It is important to study these earthquakes for further research on seismogenesis to fore-cast earthquake…