Abstract:Through statistic analysis of the precursors of 20 earthquakes in the Gansu-Ningxia-Qinghai region,it is found that earthquake precursors in this region have regional characteristics,i.e.anomalous area is small, anomaly amplitude is small, anomaly lasting time is short and seismicity period is short. Furthermore, it is found that the earthquake precursors in this region have following five common characteristics:(1)Seismicity gaps always appear before M≥6 earthquakes and with approaching to earthquake occurrence time, seismicity gaps of different magnitude earthquakes appear subsequently and nestedly from strong events to small ones.The sclerous process of medium of seismogenic zone gradually is emerged.(2) The tendency anomalies of various kinds of precursors have their own dominant patterns.(3) Before an impending strong earthquake the inverse(or accelerating) variation of ground deformation is often appearing precursor in the region.(4) Various precursors in an area have inherent harmonic identity in earthquake developing period.(5) Occurrence time and short-term precursor of a strong earthquake is relevant to some outtide factors such as magnetic storm, moon gravity and atmosphere pressure.

Abstract:In this paper,the simulation processing of CDSN digital seismic data is introduced.The CDSN digital recordings are converted into many narrow band recording modes such as SK,DK-1,DD-2,763, etc..The analogous and digital recordings are interpreted by comparing converted recordings with original recordings.The result shows that the simulation processing is effective and useful in the digital seismic data processing.

Abstract:Authors stated why the M_S7.0 earthquake in Qinghai in 1990 is renamed as the Xinghai M_S7.0 earthquake,introduced obviously precursory anomalies and recounted briefly the course of prediction before the earthquake.These precursors were underground water,vertical deformation,seismic activity,meteorological anomalies and animal behavior,etc..In the end of the article,authors stated their views about appearance of meizoseismal region during the earthquake.

Abstract:Using the data of the digital network monitoring micro-earthquake cooperatively set up by China and France, the attenuation characteristics of the Q-value of coda of microearthquakes in the area along western Haiyuan fault near Songshan have been studied. The coda Q_c values on 7 frequency bands of 170 earthquakes have been calculated. The coda attenuation in the area can be represented by Q_c=52f^1.09. It is shown that this area is a highly tectonic activity area.

Abstract:A new characteristic quantity-energy logarithm migrating parameter V value which relates time-space seismicity patterns is put forward.On the basis of time-space scanning results,V value shows an abnormal process which is normal fluctuation-tendency going down-the lowest value-tendency going up-earthquake occurring with time.Earthquakes occur during or after V value-tendency going up.Eight strong earthquakes which form 72.7 percent in total events took place during 1~24 months after the lowest V value ending.

Abstract:The characteristics of the medium-term seismic quiescence before 14 moderate or strong earthquakes in Eastern China are studied.The normalized N-T and L-T curves and the statistical parameter β_n are adopted.Each point in the isopleth map of β_n can show the level of seismic activity and its corresponding duration and end date,which can be utilized to determine the time span of the medium-term quiescence quantitatively.The several seismic activity patterns, with general feature of seismic activity rate from increasing to decreasing before the main-shocks and fluctuation variation of irregular sine wave in N-T and L-T curves,appeared before moderate and strong earthquakes are also summarized.

Abstract:Based on the data of deep seismic sounding,gravity,magnetotelluric sounding and geotherm,two comprehensive geophysical sections are established in Tianshui earthquake area.Analysing the two sections,crust-mantle structure in the Tianshui area are studied.The results show that crustal thickness along fault zone in the north edge of western Qinling is thin,and low velocity layer,low density layer and low resistivity layer synchronously exist there.The facies change transition zones of tens to a hundred kilometers in width and up to upper mantle in depth exist on the both sides of the fault zone,which means that depth of the fault zone possibly is up to upper mantle.

Abstract:The characteristics of the strong ground motion of the 1995 Osaka-Kobe earthquake (M7.2), Japan was analyzed in this paper. The results show that the peak values of horizontal acceleration in epicentral region are about 600~800 gal, the peak value of vertical acceleration is above 300 gal, the duration of the strong ground motion is about 10~15 seconds and the predominant periods is distributed from 0.2 to 2 second. The results of spectrum analysis also show that the amplitude of Fourier spectrum or response spectrum is larger than other records in a wide frequency band.

Abstract:The Seis83 programs were used in order to calculate the DSS data of Daxing-Yanqing section in Yanshan-Daxing-Yanqing profile.The structure of crust and upper mantle was obtained in Badaling and its neighborhood.The result shows that in the region,faults well developed and there is much difference in thickness of deposition layer in the shallow crust,crust structure is heterogeneous in crosswise and undulate changes of crust interface and velocity isopleth are obvious in depths,low velocity blocks exist in the partial crust.The depth of Moho discontinuity in Daxing is about 34.5 km and that in Juyongguan is about 38.5 km.A fault of Moho exists in vicinity of Yanqing.

Abstract:A calculating method for inversing body wave velocities and three-dimensional structure of interfaces by using reflected wave travel time is presented.A fast 3-D ray tracing algorithm by Chander and a damped least-squares technique are used to solve forward and inversion problems respectively.The result shows that the solutions of inversion are close quite to the true model.A 3-D Moho interface structure in Tangshan earthquake region is constructed using P_mP reflected wave data.The faults of Moho interface in Tangshan area and its vicinity are relative to the Tangshan main earthquakes and a series of aftershocks in 1976.

Abstract:The Gonghe earthquake (M=7.0) and its precursors are simulated by the finite element method in two-dimensional plane strain model. In this model, not only the effect of nonlinear, hardening, dilation of solid phase, but also the influence of water be considered, so distribution of precursors by the simulation is similar to that of fact.

Abstract:In this paper,the soil chronological method and its dating principle as well as present research situation at home and abroad and developmental prospect for application are introduced and discussed in detail.The fundamental train of thought of this method has been applied by the authors to dating study of the foreland regions of the Yumushan mountain and Altun mountain,and four quantitative relational expressions between CaO,CaCO₃ content and CaCO₃ accumulation index value in soils and their developmental age have been preliminarily formed and the mean accumulation rate of the calcic coats on gravels in soils has been obtained by statistical calculation as well.Through test and comparative analysis,it is considered that the soils chronological method is applicable to the Northwestern region of China and has the vast prospects for application.

Abstract:For several years the authors investigated and explored in loess area,collected loess samples of each type,tested the physical mechanical nature of loess in field and laboratory,and obtained a large amount of data about loess features.Based on these research results,the ralationship between physical mechanical indices of loess and its vulnerability as well as regional distribution regularity of these indices were discussed,and then their relation to geological and seismic disasters in loess area was studied.

Abstract:The formulae of stress and strain for typhoon microseism in one-dimensional simplified model are derived.The magnitude of microseism stress from typhoon triggering earthquake is calculated.The relationships between typhoons and earthquakes in time and space and two earthquake examples are analysed.Results show that it is very possible that microseism caused by typhoon triggers earthquake.

Abstract:It is studied that size of the area of region for calculating modulated small earthquake ratio using earthquake catalogue recorded by Gansu seismic network since 1988.Modulated small earthquake ratio is calculated respectively in five regions chosen in Gansu Province and its vicinity.Results show that an appliable minimum area is 6 square degree.

Abstract:A strong earthquake with magnitude of 6(3)/(4) occurred in Longxi county on March 1,A.D.138,which was the first one recorded by the Zhang Heng seismoscope.The event is made a textual research analysing historical data.The result shows that epicentre of the event with intensity of 9 degrees is between Minhe county of Qinghai Province and Lintao county of Gansu Province,and its geographical location is 35.9° north latitude and 103.3° east longitude.Regional tectonic background of the event is studied also.

Abstract:The earthquake prediction method of dynamic seismic gap with that of static seismic gap is compared in detail.Result shows the precision of epicentral location determined by dynamic gap method is higher than that by static gap method.Moreover,the former has a greater improvement than the latter in estimating occurrence time and magnitude of earthquake.