Abstract:This paper deals with the theory and method of tomographic imaging of slowness field at the Moho surface using the data of the Pn wave travelling time.In the case of slowness inhomogeneous distribution which is disturbance compared with the background,the travelling time is a linear superposition of the background,and disturbance component,and the later can be extracted from the observation.Applying.the suitable transform on the formula of the disturbance component,the form of Radon transform is obtained.Then based on the inverse projection reconstruction or inverse Radon transform,the slowness distribution can be deduced directly.

Abstract:Ten moderate earthquakes occurred in the Northwest of China after 1972 are selected,and the change of b value and the modulation shock ratio (the propertion of number of the shocks affected by earth tide to amount of all shocks) in their epicentral area is analysed in this paper.It is shown that before seven of the ten earthquakes occurred the b value of the epicentral region had obviously been correlative with the modulation shock ratio for years,and the correlation coefficients are much lager than corresponding correlativity examinati-on value for the confidence of 99 percent.The greater the earthquake is,the longer the correlation time is.
The correlation analysis of b value with the modulation shock ratio has been made in two regions,where seismic activity is more strong than other regions and seismic monitoring system is relatively perfect.After 1972 there were two periods when the correlation coefficient is larger than the correlativity examination value in above-mentioned regions,respectively.The periods correspond with the moderate earthquakes of the locality or near region.
In the light of research result of this paper,there may be the correlative change of some seismicity parameter with other ones before large earthquake occures.It might be made use of for earthquake prediction.

Abstract:Using the data of the three earthquakes (M_L>5.0) which occurred in Xunwu,Jiangxi Province in August 1987,we have discussed a travel characteristics of the π_gwave in Southeastern China.The results show that:The first velocity is 6.0km/s,it is close to Press's results;the π_g wave has shown normal dispersion,and a few are no-normal dispersion;its paramount period is 0.6-0.8 second.Using the composite amplitude of horizontal component of the π_g wave,we have obtained the radiation pattern of the π_g wave,it is basically close to radiation pattern in weak heterogeneous medium.There is the D value of time of incidence (Phase Shift) between horizontal time and vertical time of the π_g wave number.

Abstract:Based on the types of seismic structures,scale,large earthquake magnitude and cumulative seismie moment,12 large seismic systems can be divided into 4 levels.The cumulative earthquake number in a large seismic system is 7 to 10,seismic moment of maximum earthquake about accounts for 50 percent of total seismic moment.The frequency and energy characteristics have been explained by use of the concepts of fractional dimension.
The time distribution of large seismic systems has not only stoc-hastic statistic regular patterns but also certains physical laws.Large earthquakes in intraplate are of cluster character.The cumulative number N for most of large seismic systems can be a exponent func-tion of time t:
N=Ae^Bt.

Abstract:In this paper,we introduced the anomalies of the tilt before the Wuqia earthquake (M=7.4,1985),the Atushi earthquake (M=5.4,1986) and the Wushi earthquake (M=6.4,1987).The anomalous duration is about two to nine months.The anomalous magnitudes are 8.5,6.5 and 7.5 angular-sencond respectively.Meanwhile,the probable reason that produced the anomaly is analysed.

Abstract:Since half century,the unsolved principal questions in geostress measurement using borehole method are hypothesizing that the mech-anical property of rocks is isotropic,unthinking the borehole effect,unconsidering the measuring time effect and simplifying the changeful mechanical property of rocks.The maximum synthetic error caused by them can be up to 100% of principal stress value and 90° in principal stress orientation and the error can result in that the principal stress property may change from positive to negative.For purpose of high level geostress measurement,the measurement must be based on aniso-tropy of mechanical property of rocks;the borehole effect must be subtracted or avoided;the time effect in measurement be avoided or considered;the effect of changeability of mechanical property of rocks be avoided in the geostress measurement.The each component of geos-tress must be measured respectively and the fixed longterm continuous observation be made.

Abstract:During working in field,the author has often seen some faults with steep dip angle which appear the form of normal fault but have the squeezed feature.The stress action way mirrored by the faults is contrary to regional stress field.Based on the functions of mechanical properties of rock bodies and their changes in tectonic activities,these contradiction phenomena are discussed.The mechanical properties of rock mainly include the gravity of rock body and the stress relaxation,and the author considers the relaxation in rock is caused by both aspects of rheology and non-rheology.Based on the idea,the relations between these factors and seismic activities are discussed,and some practical tectonic phenomena also are analysed.

Abstract:This paper has made a brief introduction to the main achievements and development of the comprehensive earthquake prediction in the Northwestern China.The analyses show that in the aspect of interme-diate-long term tendencies,there is elementary surveying foundation for most destructive earthquakes (M≥5).The results of the comprehensive observation have basically passed statistical tests.There is elementary surveying foundation of short-imminent precursor networks for earthquakes (M≥6.5) only within Urumqi,Lanzhou,Xi'an,Wuzhong and Wudu districts.From 24 seismic cases we get 73 items of intermediate-long term tending anomaly data which are mainly seismometrical ones,53 items of short-imminent anomaly data which are mainly groundwater level,radon,telluric current,This paper has summarized the chief features of temporal and spatial distribution about the anomalies and discussed the new problems and new directions in the comprehensive seismic predictions.

Abstract:Based on the summarizing tectonic features in Ordos region,the authors advance following views.relating the tectonic mechanics speci-fic property to the earthquake strength.
1.The maximum magnitude of earthquake that will happen on the tension fault or fault zone will be smaller than 7.
2.The maximum magnitude of earthquake that will happen on shear fault or fault zone will be 7-8.
3.The maximum magnitude of earthquake that will happen on the press fault or fault zone will be bigger than 8,may be 8½.
According to these rules,the authors have predicted potential seismic focus place of different magnitudes in Ordos region

Abstract:In this study,we present a quantitative method which can estima-te the opinion of the earthquake prediction by using a series of for-mulas to calculate the rates of determination,precision and success for various opinions in earthquake prediction.Finally,as an example,the rates of determination,precision and success for annual earthquake prediction in China from 1975 to 1984 have been calculated and analysed.The results show that the level of the seismic midterm prediction in China is still very low.

Abstract:实验场地位于福建省南靖县汤坑盆地中央。盆地内分布有F₁、F₂、F₃和F₄ 4组断、裂,其中F₁为张性兼压扭性断裂,F₂为扭性断裂,F₃为张扭性断裂,F₄为压扭性断裂(图1)。

Abstract:在1976年8月16日、22日松潘发生的两次7.2级地震前,静宁地应力电感曲线显示了明显的异常,并据此在震前提出了预报意见。本文对该异常形态特征进行了分析研究。

Abstract:为了给西安市地震小区划提供场地土的动力参数,我们采用应力波检层法,现场唤测了西安市场地土的地震波速。击振方式为木板敲击法。

Abstract: