The success of the prediction of Haicheng earthquake and the negligence of the Tangshan earthquake

The success of the prediction of Haicheng earthquake and the failure of the prediction of Tangshan earthquake were both well known in the world. What happened, why such a strong earthquake as occurred in Haicheng had been predicted successfully and with a small loss of lives and property? Why a successively strong earthquake about a year later in a region not so further was failure in the imminent stage of prediction and there were so many fatalities and a great degree of property? The author addresses these points based on these true experiences including the first hand experiences leading up to, during, and following these two earthquarter. In addition, he also introduced some seimic phenomena which he had seen after Chi-chi earthquake in Taiwan.

Crack－induced anisotropy in the crust from shear wave splitting observed in Tangshan region，North China

Using the cross correlation function analysis method, this paper discusses shear wave splitting and crack-inducedanisotropy in the crust beneath Tangshan, North China, by the digital data from Tangshan strong ground monon temporary arrays. Sixteen of twenty-one stations in the arrays recorded earthquake events available forstudying from 1982 to 1984. Having calculated 131 available records, we get slower shear wave time delay r andfaster shear wave polarization azimuth Paz in Tangshan region, and the cracks density s is got further fromthem. The analysis shows that the stress field is very complicated in Tangshan region and has strongly regionalfeature. Because of the complicated distribution of faults, different shear wave splitting characteristics are shownin 16 stations, scattered r and different Paz. And they also were observed that the r and PaZ values were diversewithin the time scale of hours in more than one station. In Tangshan region the average results of r, Paz and Bare 0. 0071 s. km-1, northwest-west near to east-west and 0.022 respectively. Meantime, the standard devia.tions were calculated in this paper.

Recurrence Characteristics of Major Earthquakes in the Tangshan area,North China

The Tangshan area lies in the North China plain where an Ms 7.8 earthquake occurred in 1976, which is associated with a hidden active fault. To reveal the recurrence characteristics of major quakes in this area over a relatively long time, we have conducted a comprehensive study using geological investigations, shallow seismic exploration, boreholes, trench observations and geological dating. Five paleoearthquakes were recognized in a 6.4m-deep trench west to the Tangshan Asylum. Among them, the former three events occurred between 56.78 ＋ 4.83ka and 89.39 ~ 7.60 ka, and the fourth event occurred around 6.9 ka, respectively, and then followed by the fifth in 1976. Seven boreholes were deployed crossing the ground fissure formed by the 1976 Tangshan earthquake at the site of No. 10 Middle School, where we have identified 25 liquefaction events in the boreholes TZC6-5 and 6-7. By the comprehensive analysis of the trench, the liquefaction events from the boreholes and the depth-time curves of drill cores, we suggest a new recurrence model of major quakes in this area. It is not a constant recurring cycle since 210 ka, instead consisting of six alternating seismically quiet and active stages. Of them, stage I （〉177 ka） was a quiescent period in seismicity, stage II （from 143 ka to 177 ka） was an active one, stage III （from 102 ka to 143 ka） was quiescent again, stage IV （from 56 ka to 102 ka） had many quakes, stage V （from 6.9 ka to 56 ka） became quiet, and stage VI （from 6.9 ka to now） was the beginning of a new seismically active period.

Numerical simulation of dynamic process ofthe Tangshan earthquake

In this paper. :LDDA (Lagrangian Discontinuous Deformation Analysis) method is used in modeling thedynamic process of the M,=7.8 Tang shan earthquake on July 28, 1976 and obtain directly the dynamic and quasi static dislocations. shear stress drops, fracture velocities of the Tang shan earthquake fault. The simulation showsthai the slip history at each point of the fault is different. The displacement vectors at the concave side of the faultis greater than that of the convex side of the fault. The 'over shoot' of the fault slip is greatest at the middle part ofthe fault and attenuates to its ends. The rupture velocities of the fault from the epicenter towards south-west andtowards north-east are 3.08 m/s and 1. 18 m/s, respectively, the average one is 2.13 In/s. The maximum dynamic.m quasi-static dislocations are 7. 1 m and 6.2 m respectively. the average quasi-static one on the fault is 4.5 m.initial stress dynamic and quasi-static shear stress drops are 8.1 M Pa and 5.4 MP4 respectively, the averagequasi-static shear stress drop is 3.9 M Pa. We found that the rupture velocities and shear stress are related to theinitial stress states of the fault.

The mechanism of regional gravity changes before and after the Tangshan earthquake

There were 34 times repeated gravity measurements along Beijing, Tianjin, and Tangshan from 1971 to 1981. The gravity field around the Tangshan area continuously increased about 98×10 -8 m·s -2 from 1971～1975. The peaks of the gravity changes occurred in the middle of 1975. Preliminary study of mechanism of the gravity changes before and after the Tangshan earthquake was done with combination of deformation and seismic data in the area. The final results show that the deep boundary surface up lifted with a rate of 2.5 m/a in the Tangshan area from 1971～1975.

Pedigree and Germplasm Base of Inbreds of the Tangshan Sipingtou Heterotic Group of Maize in China

The Tangshan Sipingtou (TSSPT) germplasm in inbreds of the Tangshan Sipingtou heterotic group of maize in China was mainly derived from Huangzao4, and the source of TSSPT germplasm was severely restricted by the inbred Tangsipingtou. Except Tangsipingtou, the contents of TSSPT germplasm were only 50% or less in inbreds of this group, with the existence of more than 20 non-TSSPT gennplasms which resulted in abundant genetic diversity in this group. 95.22% inbreds of this group contained both TSSPT and UNS(unknown source) gennplasms in the ratio of 1 :1, with 12. 5 - 50% of each germplasm. The recombination of TSSPT and UNS germplasms had produced Huangzao4, the most important maize germplasm of compact plant form. About 90. 24% of the inbreds in this group were the inbred Huangzao4 and its derivatives. 11.11% of the derivatives contained 25 - 50% of Luda Honggu(LDHG) germplasm, and 16.67% of the derivatives contained 12. 5 - 25% Creole and 6. 25 -28.13% LSC germplasms. In addition, 97. 56% of the inbreds of this group contained one or more non-TSSPT germplasms. This indicates that the germplasm base of inbreds of the TSSPT heterotic group had changed and evolved away from actual TSSPT germplasm.

Regional seismicity triggered by the M_s=7.8 Tangshan event on July 28, 1976 and the stati cstress field change

We studied the seismicity before and after the M_s=7.8 Tangshan event on July 28, 1976 (39°28'N, 1 18° 11'E) and the results show that in 3 regions outside of the source zone, seismicity rate increasing were observed, which was significant in 0.99 significance level using Z-statistic test and was proposed to be triggered by the M_s=7.8 Tangshan earthquake. The magnitude of the greatest triggered event was 5.5. The epicenter distances of these earthquakes were several ten kilometers to 300 km. The static stress change △CFS of Coulomb failure was calculated using an elastic dislocation model in half space and the △CFS on the major rupture directions in these three regions were positive.

The variations of the degree of ground resistivity anisotropy during the Tangshan earthquake

Based on the geoelectric observation data of the 1976 Tangshan earthquake of M=7. 8 compiled by the Research Group on the Geoelectricity of the Tangshan Great Earthquake, a dimensionless factor S has been defined as the degree of ground resistivity anisotropy. The S values during the generation process of that earthquake have been calculated and their variations have been analyzed. The result has showed that the variation of the degree of ground resistivity anisotropy existed throughout the process of generation and occurrence of the Tangshan earthquake and the features of its pattern are representative. The S value can therefore be taken as a new precursory factor of earthquakes which can be applied together with other dimensionless factors in the analysis and prediction of earthquakes. A physical explanation of the variation of the S value has also been given.

Land use suitability analysis for town development planning in Nanjing hilly areas: A case study of Tangshan new town, China

Land use suitability analysis plays an important role in sustainable land use and solving environmental problems caused by rapid urban development.A land use suitability mapping approach for town development planning in hilly areas was constructed based on two multi-criteria evaluation methods:Weighted Linear Combination(WLC)and Ordered Weighted Averaging(OWA),to comparatively evaluate and map land use suitability of Tangshan new town in Nanjing,China.Fourteen evaluation factors related to topographic,environmental,socio-economics and historical sites data were used as suitability criteria.The analytic hierarchy process(AHP)method and GIS techniques were integrated into the evaluation models to create the land use suitability map for town development planning.The results of WLC approach showed that 11.4%of the total area is highly suitable while the 48.6%is unsuitable.The results of WLC and OWA approach showed the distribution of degree of land use suitability is almost the same.The areas located at the southern and eastern flat regions are highly suitable for land use,whereas the areas close to the mountain forests,steep slopes,waters,and hot springs,have lower suitability for land use.Sensitivity analysis indicated that the suitability results of the two proposed methods are robust.Indirect validation was achieved by mutual comparison of suitability maps derived from the WLC and OWA methods.It demonstrated that the overall agreement is 90.81%and kappa coefficient is 0.81,indicating that both methods provide very similar spatial suitability distributions.By overlaying the resultant map with the previous master plan map of Tangshan new town,the overlay map once again indicated a satisfactory ecological fit between the two maps.At last,several recommendations are proposed aiming at improving the long-term town development plan for Tangshan new town.

Kinematic features of the seismogenic fault of the Tangshan earthquake and the recurrence period of large earthquakes

By the inversion method of uneven slippage of faults in the depths(Liu et al ., 1995) and using the crustal deformation data of six phases, the movement states of seismic fault of the Tangshan earthquake in five time periods before, during and after that earthquake are computed. The result of computation has revealed the movement process of seismic fault, during which the fault moved at an increasing rate before the quake, slipped suddenly during the quake, and became relaxed, adjusted and stabilized gradually after the quake. Moreover, the recurrence period of earthquakes in Tangshan is computed using the relation that the slippage of seismic fault bears with strain energy.

The numerical simulation of thesource development of the Tangshan earthquake

According to the precursory data of the 1976 Tangshan earthquake( M =7.8), and combining with the research results of rock fracture, seismic source, tectonics, seismic precursors, dynamic condition and crust structure, the seismogenic process of Tangshan earthquake has been numerically simulated by using the model of water saturated porous medium with a rhombic hard inclusion. First, a system of seismogenic dynamics equations of solid liquid two phase medium has been set up under considering rock inelastic dilation, strain softening and pore water permeation. Then, the finite difference method to solve the equation system in incremental form has been presented. Finally, the seismogenic process of Tangshan earthquake and the temporal spatial characteristics of its precursors have been numerically simulated when the hard inclusion includes a soft fault belt. The numerically simulating result shows that the development of Tangshan earthquake mainly undergoes following processes: elastic accumulation, early inelastic cubic dilation, accelerative softening (failure and creep) of fault first time, inelastic dilation twice in Tianjin—Ninghe area, accelerative softening of fault twice and instability. Corresponding to the fault accelerative softening, elastic recovery and inelastic dilation twice in some parts of seismogenic medium. By comparing with the data of precursory observation, ones can find the preceding simulating result explains the varied characters of practical data better. Meanwhile, the numerical simulation further displays the temporal spatial change law and complex patterns of the field of Tangshan earthquake development as well. It makes a base study for the physical mechanism of change of the seismic precursory field.

Synthesis of accelerations of the 1976 Tangshan earthquake(M_S 7.8)in near-and far-field by using semi-empirical method

In this paper a heterogeneous fault model of the Tangshan earthquake is suggested, which consists of two southern sub faults striking N30°E and two northern sub faults striking N50°E. Total length of the main shock fault is 114 km and seismic moment is about 1.4×10 20 N·m. The epicentre of the main shock is located at the southern part, near the intersection of the two bands. Accelerations of two aftershocks ( M L 5.5, M S 6.9 ) were used as empirical Green's functions to synthesize the accelerations of the main shock in near and far field. A method that small events and main shock are considered not satisfying the similarity relationship in the improved empirical Green's function is also applied in this paper. Peak values, duration and response spectra of synthesized accelerations in far field are in agreement with the observed records. The synthesized results in near field are also in agreement with the epicentral intensity distribution of the main shock. The results show that the peak acceleration of Tangshan earthquake in epicentral region exceeds 1.1 g. It is consistent with the peak accelerations recorded in some large earthquakes occurred in recent years.

Tectonic setting of the seismogeny of the 1976 Tangshan,ChinaM=7.8earthquake

Based on the analysis of multi-temporal and multi-spectral satellite images for North China region, we have found that one year and more before the occurrence of 1976 Tangshan earthquake, the anomalies of electro-magnetic radiation on the satellite images indicated that the NE-trending Tangshan fault zone was dissected by the NNW-trending Nantai-Tangshan fault, and the Changping-Fengnan fault was dragged to form an arcuate bending at Fengnan. All these indicate the right-lateral translation along the Tangshan fault in NE direction. In order to gain an insight into the features of these faults, a shallow seismic exploration along the Tangshan and Changping-Fengnan faults has been carried out. The results have indicated that the NE-trending Tangshan fault is a high angle right-lateral strike-slip normal fault, dipping northwest, while the NWW-trending Changping-Fengnan fault is a southwest-dipping left-lateral strike-slip normal fault.

Two-step interface and velocity inversion—— Study o e of the Tangshan seismic region

This paper studies the computation method of two step inversion of interface and velocity in a region. The 3 D interface is described by a segmented incomplete polynomial; while the reconstruction of 3 D velocity is accomplished by the principle of least squares in functional space. The computation is carried out in two steps. The first step is to inverse the shape of 3 D interface; while the second step is to do 3 D velocity inversion by distributing the remaining residual errors of travel time in accordance with their weights. The data of seismic sounding in the Tangshan Luanxian seismic region are processed, from which the 3 D structural form in depth of the Tangshan seismic region and the 3 D velocity distribution in the crust below the Tangshan Luanxian seismic region are obtained. The result shows that the deep 3 D structure in the Tangshan seismic region trends NE on the whole and the structure sandwiched between the NE trending Fengtai Yejituo fault and the NE trending Tangshan fault is an uplifted zone of the Moho. In the 3 D velocity structure of middle lower crust below that region, there is an obvious belt of low velocity anomaly to exist along the NE trending Tangshan fault, the position of which tallies with that of the Tangshan seismicity belt. The larger block of low velocity anomaly near Shaheyi corresponds to a denser earthquake distribution. In that region, there is an NW trending belt of high velocity anomaly, probably a buried fault zone. The lower crust below the epicentral region of the Tangshan M S=7.8 earthquake is a place where the NE trending belt of low velocity anomaly meets the NW trending belt of high velocity anomaly. The two sets of structures had played an important role in controlling the preparation and occurrence of the M S=7.8 Tangshan earthquake.

Characteristics of coseismic water level changes at Tangshan well for the Wenchuan MS_8.0 earthquake and its larger aftershocks

Coseismic water level changes which may have been induced by the Wenchuan Ms8.0 earthquake and its 15 larger aftershocks （Ms〉5.4） have been observed at Tangshan well. We analyze the correlation between coseismic parameters （maximum amplitude, duration, coseismic step and the time when the coseismic reach its maximum amplitude） and earthquake parameters （magnitude, well-epicenter distance and depth）, and then compare the time when the coseismic oscillation reaches its maximum amplitude with the seismogram from Douhe seismic station which is about 16.3 km away from Tangshan well. The analysis indicates that magnitude is the main factor influencing the induced coseismic water level changes, and that the well-epicenter distance and depth have less influence. Ms magnitude has the strongest correlation with the coseismic water level changes comparing to Mw and ML magnitudes. There exists strong correlation between the maximum amplitude, step size and the oscillation duration. The water level oscillation and step are both caused by dynamic strain sourcing from seismic waves. Most of the times when the oscillations reach their maximum amplitudes are between S and Rayleigh waves. The coseismic water level changes are due to the co-effect of seismic waves and hydro-geological environments.

Crustal deformation of seismogenic fault and its surrounding area after the Tangshane arthquake

The fault deformation observed in 18 years after the Tangshan earthquake on the deformation station located on the surface fissure of the seismogenic fault is introduced. The results show that the vertical and horizontal deformations of the seismogenic fault were concentrated within 7 years after the earthquake and the year of 1983 was the turning year of postseismic deformation. The deformation shown by large area levelings is consistent with the intensity level of fault deformation. At present, a relaxation state appears in which stress is not easy for stress to accumulate and there is no probability of stronger earthquake occurrence in the near future.

Evolution characteristics of seismic intensity in Tangshan seismic zone

１ＴｈｅｕｓｅｄｄａｔａＴｗｏｃｏｐｉｅｓｏｆＣｈｉｎａＥａｒｔｈｑｕａｋｅＣａｔａｌｏｇｕｅｓｅｄｉｔｅｄｂｙＰｒｏｆｅｓｏｒＧＯＮＧＸＵＧＵｗｅｒｅｕｓｅｄｆｏｒｔｈｅｄａｔａｂｅｆｏｒｅ１９７９；ＣｈｉｎａＥａｒｔｈｑｕａｋｅＣａｔａｌｏｇｕ...

Spatio-temporal epidemic type aftershock sequence model for Tangshan aftershock sequence

Shallow earthquakes usually show obvious spatio-temporal clustering patterns. In this study, several spatio-temporal point process models are applied to investigate the clustering characteristics of the well-known Tangshan sequence based on classical empirical laws and a few assumptions. The relative fit of competing models is compared by Akalke Information Criterion. The spatial clustering pattern is well characterized by the model which gives the best fit to the data. A simulated aftershock sequence is generated by thinning algorithm and compared with the real seismicity.

3-D structural reconstruction of Moho in the Tangshan earthquake area by using inversion of curved interface

A method for inverting 3 D curved interface and layer velocity by using travel time of reflected waves is studied. Each interface is described with sectional, incomplete cubic polynomial. A fast 3 D ray tracing method is used in forward problem, and a least squares method with variable damping is adopted in the inverse problem. Result from numerical modelling shows that the solution can converge fast on the true model. Observational data from the Tangshan earthquake area are processed, 3 D Moho discontinuity in the area is rebuilt, and finally, the relationship between the regional structure and seismicity is revealed.

Comparison and analysis of the stress field in the source region of Tangshan and Lancang earthquake sequences

The state of the stress fields in the source region is analysed systematically, on the basis of the focal mechanismsof 167 events with Ms≥4. 0 of Tangshan sequence and 163 moderate-small events of Lancang sequence respectively. The result indicates that the directions of the stress field in the source region are generally stable and thevariation is not obvious after the occurrence of strong shock. The dominant orientations of focal mechanisms ofthe aftershocks are consistent with that of the mainshock, there is still a small difference between some mechanisms of aftershocks and the mechanism of mainshock, and the difference decreases as time goes on. The numbers of solutions with dominant direction of Tangshan and Lancang sequences are similar to each other, it indicates that the controls of the strong earthquake sequences from the tectonic stress field are similar to each othertoo. Through the hierarchical clustering analysis of focal mechanism,it is found that the number of clusters ofTangshan sequence is larger than that of Lancang sequence,and their orientations are relatively disordered. Itmay be the cause that the tectonics in the Tangshan region are more complicated than those in the Lancang region.