Abstract:Partial melt models in different geometrical configuration and distribution are established.The geometrical distribution and the connectiveness of the melt are determined by three factors:① the location of melt;② the melt fraction;③the minimum total free energy of the solid-solid and the solid-liquid interfaces.The melt geometries are films,tubes and isolated ellipsoidal inclusions.The bulk and shear moduli and conductivity in partially melted rocks are calculated by using the models.The v_p,v_s and ρ are calculated by choosing parameters in the lower crust on both sides of the northern segment of North-South seismic zone,i.e.,in the lower crust of Ordos platform v_p≈ 6.71 km/s,v_s≈ 3.96 km/s,resistivities are from one hundred Ωm to several hundreds Ωm,in the fold systems of Qilian and Qinling 6.4 km/s ≤v_p ≤ 6.6 km/s,3.72 km/s ≤v_s ≤ 3.89 km/s,resistivities are from several Ωm to dozens Ωm.The results of numerical modelling agree with that of geophysical inversion for the most part,the geotectonics are explained qualitatively.The combined numerical modelling of velocity and resistivity in lower crust by using a model shows that the model is available in interpretation of v_p,v_s and ρ.

Abstract:In order to study deeply the dependence of the velocity and attenuation of elastic waves in rocks on fluids,the distribution and viscosity of fluids must be considered.The authors introduced a gas pocket model to investigate the dependence of the velocity and attenuation of P waves on viscous fluid distribution,described the uniformity of fluid distribution with average bubble radius,calculated the curves which related velocities and attenuation with saturation under different bubble radius and pressure frequency and compared gas pocket model with effect fluid model.Because Gassmann equation weren't applicable under high-frequency pressure due to the local flow,the theoretical curves were corrected with the P wave and S wave velocities in dry and saturated sands.The saturation dependence of the P wave velocity and attenuation is measured and the attenuation was attempted to derive by using amplitudes of the peak frequency.The attenuation at dryness and saturation and the attenuation law from dryness to saturation are the same as those by spectral ratio method,but amplitude of the peak attenuation is different.By regressing measured velocity and attenuation with theoretical curves and computing the average radius of bubbles.It is considered that the saturation dependence of velocities and attenuation is related with pressure equilibration between gas and liquid in sands.

Abstract:A large number of seismologic windows in a great area,especially in the Tianshan earthquake belt,show ed clear anomaly during the Jiashi strong earthquake swarm from 1997 to 1998.Strong earthquakes of the swarm can be divided into five groups according to the occurrence time.The first strong earthquake of each group can be checked out by the monthly and ten-days microseism frequencies of Kashi and Atushi seismic window s.The succedent strong earthquakes of each group can be checked out by the daily microseism frequency of the Kashi and Atushi seismic window s.It can be found from the anomalous features that strong earthquakes occurred usually after a high value of monthly frequency or after a low value of ten-days frequency and after a low value of daily frequency.It can be also found from the temporal process of the window anomalies that the duration and interval of the anomalies of Kashi and Atushi seismic windows during Jiashi earthquake swarm are longer than those of a single event.The duration of the anomaly during the first strong shock of each group is longer than that of the succedent strong earthquake.The daily frequencies of the two windows notably increased before the succedent strong earthquakes occurred from the exponential attenuating background in 1997,but in 1998 the daily frequencies increased before the strong earthquake occurred in the normal background.The results of the analyses indicate that the earthquake window is a valuable method in earthquake prediction.

Abstract:The relationship between seismicity enhancement parameter W₁ and corresponding seismicity parameters,and their variation before some earthquakes about M_S6.0 are analysed in this paper.The results show that there are three forms on enhancement of seismicity before moderate or strong earthquakes,the first is the enhancement on magnitude,the second is the temporal and spatial cluster of seismicity,the third appears as the first and the second forms concurrently.The variation of dynamic pattern of W₁ value before some earthquakes about M_S6.0 shows that seismogenic process is an evolution process of interaction of many stress concentration zones.

Abstract:The short-impending predictions and their reasons to the M_S5..4 earthquake on Nov.29,1999 and M_S5.1 earthquake on Jan.12,2000 in Xiuyan of Liaoning province are written in detail in this paper.The comparison between forecasts and actual earthquakes shows that the distribution character of local mean lunar times of significant earthquakes is a better indication of short-immediate term forecast and the judgement of the trend after a large earthquake happened is often difficult and needs comprehensive analysis.We ought to judge the type of an earthquake based on the characteristics of the earthquake itself and the type of the earthqaukes in history may be only available for reference.We ought not to consider that the earthquake has been in the later weak stage if there are different views and some few suspicionsness of the earthquake sequence.

Abstract:The effective stress formula of the earth crust having the faults with different direction and size is deduced by geometry damage theory and method,and the theory and method to analyze and compute the uncontinuous faults in the earth crust by geometry damage theory is discussed.At the same time,the earth stress variation in Jiashi area,Xinjiang,is computed by geometry damage theory with GPS data.Comparing the computed results with M_S>5.0 earthquake activities in the region from Jan.1997 to Dec.1998,it is seen that modern strong earthquakes in the south of Xinjiang mainly occurred in the region where the stress field variation is very large.

Abstract:The characteristic earthquake model is set up by using paleoseismic and historical earthquake data of the West China.The seismic hazard of Xianshuihe-Xiaojiang fault zone located on eastern margin of Qinghai-Tibet Plateau was estimated based on the mixed seismic model composed by characteristic earthquake model and magnitude-apart Poisson model.Having com pared with the seismic zonation map of China published in 1990,it is shown that both seismogenic probability and area of the region with I=8 obtained from the mixed model are larger than those on the seismic zonation map.That is to say,the leaving time and recurrence period influence on seismic hazard assessment.Therefore,the no nrecalibility of Poissin model could be solved by using characteristic earthquake and the mixed model,and scientific and reasonable results could be obtained.

Abstract:Based on the coupling relation between bulk dilatation ratio and water level variation,the water level variation of Baoshan well is simulated by using finite differential method.The original water level data is sampled during the preparation and occurrence of the Menglian M_S7.3 earthquake on July 12,1995 and Lijiang M_S7.0 earthquake on Feb.3,1996.The variations of the average stress rate near the well are obtained by fitting the simulated curves with practical measurement curves.

Abstract:The artificial neural network can complete the news treatment of the whole network by means of a mutual function between the neural units,and has a lot of merits of self-learning,self-adjusting and suchlike.Therefore it is feasible that the seismic activity is researched by the neural network.The analysis system based on the neural network is initially set up and an applied example is put forward in the light of the problem of seismic activity.

Abstract:Eshelby's theory of elastic field containing elliptic inclusion is derived in detail and the effective elastic modulus of cracked media (the first order of Hudson equation) is derived based on Eshelby theory.The purpose is to complement the Chinese documents in this field and to illustrate the basis and meanings of relative equation for further correct application.

Abstract:According to the relation between the peak velocity and the tectonic shear stress,a preliminary estimation of shear stress distribution in Guanzhong region of Shaanxi province is made by using data of small earthquakes from Xi'an digital seismic network.The results show that the shear stress level is lower in central area of Guanzhong and the possibility of large earthquake in this area is lower than the other areas.The areas with relatively higher stress level are Hancheng in northern Guanzhong,Baoji-Qianyang in the western part and Dali-Huayin in the eastern part.In these areas,there exists the potential of earthquake with magnitude about 5.

Abstract:The model of accelerating seismic activity,which is set up on the basis of fracture theory and experiment of rock,stands on the solid ground of physics.Its use in analyzing and forecasting the future seismic activity is of great significance in practical application.In this paper,we analyzed and forecasted the seismic activity in East China region and seismic zone from Changjiang mid-downstream reach to south Yellow Sea by using the model.It is indicated that the present seismicity period will finish about in 2016,and earthquakes whose whole energy is corresponding to that of an earthquake with M_S7.7 will occur from now to 2016.It is also indicated that the value of characteristic parameter α=4,which characterizes the regional seismic activity in the model of accelerating seismic activity,is suitable to East China region and seismic zone from Changjiang mid-downstream reach to south Yellow Sea.

Abstract:The displacement along the south Altun fault in the Annanba basin was investigated.The result reveals that the offsets of terrances T₁,T₂,T₃,T₄ and T₅ are 2.5 m,23 m,48 m,96 m and 185 m respectively.The biggest offset is determined to be 3500 m,which suggests a slip rate of about 3 mm/a.

Abstract:Based on the space-time rhythmical features of seismic activity in West China and its neighboring areas,the authors study in detail the space distribution of the equally spaced strong earthquakes,strong earthquake belts and 23 years solar cycle in the regions and analyse migrating laws of the main active region in active periods.It is considered that the fifth earthquake activity period is over about in 2005,the main active area is Tianshan seismic belt and there may be energy release of a M_S ≈8 earthquake in the future several years.

Abstract:The activity information of strong earthquakes (M_S≥6.5) in Taiwan reg ion in the 20th century is researched.The result shows that strong seismicities in Taiwan region in the 20th century have the characters of zonation,substage and migration.The reason that produces the characters is explained.

Abstract:Based on the study of the regional tectonic framework and investigations of the Lijiang M_S7.0 earthquake in 1996,the earthquake generating environments are systematically analyzed.Under the action of potential regional nearly NS compressive stress field,the sinistral slip of the NE-strike Lijiang-Xiaojinhe fracture and rig ht-lateral slip of NW-strike Zhongdian-Yongsheng fracture resulted in local and extension environment in the eastern triangle end of Yulongxueshan-Jiuzihai faulted block,at last the no rthend of the nearly NS-strike and dipping-westw ards Yulong xueshan's east piedmont fault was ripped up and the Lijiang M_S7.0 earthquake happened.

Abstract:The structural aerogeochemistry process along the earthquake-generating fault of the Haiyuan (M_S8.5 earthquake) in 1920 is discussed based on the exprimental result.The degassing on the Haiyuan active fault is mainly crust degasification,in which the contents are mainly from middle-upper crust.The degassing intensity is closely correlated to the fault stress state as well movement characteristics.The different degassed elements reflect different depth and characteristics.Radon reflects shallow depth and tension,mercury and Helium reflect relative deep depth,and hydrogen reflects obduction or nappe or rock-water reaction on the fault surface.

Abstract:The principle of the earthquake prediction (warning) system is introduced and the system effect of reducing the injuries and deaths is analyzed and the ratio of reducing injuries and deaths (P value) may be beyond 70% in the M_S8 earthquake.It is found that the maximum of the seismic hazard and P value are in the middle intensity area,and not in the higher and the lower intensity areas.

Abstract:By the com prehensive study of geology,geomorphology,physical probing,trenching and boring,a subsurface fault is found along the west edge of Qinwang chuan basin,which stretches to the NNW and crosses the site of Zhongchuan airport extension.Some related issues of the fault,such as the dimension,segmentation and active time are investigated in detail and the effects of the fault to the site are scientifically evaluated.

Abstract:Firstly,the loess site of seismic subsidence of the Yongdeng earthquake in 1995 is investigated,and based on the PGA and the loess's thickness of the site,the value of loess seismic subsidence is calculated by using the relationship of σ_d versus ε_p of the earthquake site.Secondly,the formation mechamism of loessial seismic subsidence is studied by comparing the micro texture of undisturbed loess with the seismic subsided one.The result shows that the value of loessial seismic subsidence calculated using the test curve is smaller than the value of seismic subsidence caused by the earthquake.When exposed to dynamic stress,the void structure of loess will be destroyed by shear stress and become denser under the gravity force.This is the mechamism of loessial seismic subsidence.

Abstract:The author has discussed the present situation of travel time tomography of body wave in China region in details by dividing the region into the east and west parts.Some features of the three-dimension velocity structure in China have been summarized:the velocity image displays clearly the lateral heterogeneity in the crust and upper mantle,which persists down to 1 100 km deep;there is a correlation between the velocity image of the shallow part and the known geological features;there is also a correlation between the velocity image and seismicity;the lithosphere thickness and the crust thickness change,and so on.Finally,the features of tomography in the present researches in China and it's possible development tendencies have been analy sized.

Abstract:The basic principle and linking method of the data composite and decom posite technology are expounded.The MPX1059 data compounding equipment is applied in relay transferring of the Hefei digital radio-linked telerecording seismometer network and good results have been achieved.

Abstract:Time-frequency analysis method is further expansion of Fourier transform.Earthquake signals may be decomposed into different frequency section on time-axis by time-frequency analysis method.Emulation study results show that time-fequency analysis method has a series of advantages while FFT methods do not have.The method is very effective in signals analysis.

Abstract:30多年来,虽然中国学者已成功地或较为成功地预报了多次中强地震,但是,地震预报并没有在理论上和实践上有所突破,因此,目前对大多数破坏性地震仍然不能作出较为准确的预报.

Abstract:Ordos block is a single and strongly active block.On the basis of the achievments in scientific research concerned,it is proposed that Ordos block attends medium-term seismologic consideration as an independent region unit.It is significant for judging the seismic trend in the present region and the whole country.

Abstract:Ordos block is a single and strongly active block.On the basis of the achievments in scientific research concerned,it is proposed that Ordos block attends medium-term seismologic consideration as an independent region unit.It is significant for judging the seismic trend in the present region and the whole country.