Abstract:The time-space evolutions of the short-impending anomalies of the five kinds of precursors which include geoelectricity,hydrochemistry, ground water behavior, ground stress and ground de-formaticn around a strong earthquake are depended upon the active master structures and the gen-erating-earthquake mechanism.The evolutions of the far-field abnormalities of the precursors are related to the structures and the abnormalities at different structures have the diversity of evolu-tional time. In some particular years one-year scale anomaly of earth resistivity demonstrates the anomaly fastigiums which are synchronous with the years when energy of M_s≥5.0 earthquakes is up to that of a M_s=7.0 earthquake or are delayed one year. The fastigiums and the years are fairly corresponding to the years of the acceleraticn of the earth rotation. According to the research results of the two respects, 12 strong and moderate earthquakes are predicted so that 10 shocks of them occurred in the predicted area and the predicted time interval (a half year or one year time interval).The sites of seven shocks are basically exactly predicted and those of three shocks are fairly exactly done.

Abstract:Using the small earthquake records from March 1988 to March 1991 from seismic network that was established jointly by China and Japan, source spectra and source parameters of small lo-cal earthquakes in Xi'an and its surrounding region are calculated and the relations between the source parameters and magnitude M_L are analysed.

Abstract:Combining the variations of earthquake intervals and magnitudes. the activity features of mod-erate or stronger earthquakes in whole country and the main seismicity areas in China during this century are analyzed Most of intervals are within 5.5a, more than half are within 2.5a, and the maximum valve of interval is near 18a. After 1950s, activity weakened obviously for earthquakes of M ≥7.5 and M ≥7.0 all over China, M ≥7.0 in Qinghai-Xizang block (QXE), and after 1970s, it did so for shocks of M ≥7.0 in Taiwan, M ≥6.0 in North China, and M ≥6.0 in Sichuan. The influence of strong earthquakes which occurred in northern part of QXB from 1920s to 1930s on the seismicity of this region ended in 1970s, then, activity of 5.0 ≤ M ≤ 6.5 earth-quakes strengthened from 1980s clearly. The high tide of Yunnan seismicity formed after 1970s, in fact, was enhanced from 1960s. The typical process of strengthening before strong earthquakes is showed in North China and Taiwan, and that of attenuation after strong earthquakes is showed in Ganst-Ningxia-Qinghai (GNQ), The stress field of great triangle region, stress field of east part and the global scale stress field which are controlling the seismicity all over China have a stable pe-riod about 20a for a long time, while the later delayed about 1/4 period for the former in proper order, and the two former played a leading role. The seismicity along the eastern and northern edge of QXB include the important roll of QXB crust matter flowing toward east besides influence of stress field in east part. We should follow with interest the possibility of Sichuan M ≥6.0, GNQ M≥6.0 Gansu M ≥5.0 and Xinjiang M≥ 7.0 earthquakes in future years.

Abstract:Based on the dynamic equation of the seismic energy accumulation, a method for estimating the strong earthquake recurrence period by the fractal principle has been deduced in this paper. The strong earthquake recurrence period can be precisely estimated from the recent complete mi-croquake data by the method. An example has been analyzed in order to test reliability and practi-cality of the method.

Abstract:The north latitude 35° line is a special earthquake activity belt. The convection direction of asthenosphere in upper mantle bends just near the line. Study results show that activity pattern of asthenosphere in upper mantle along the 35°N line is closely related to earthquakes.

Abstract:The gravity variation before and after the Lijiang M_s7.0 earthquake that province occurred in Yunnan in 1996 is calculated by wavelet analysis method and the relationship between different wavelet transformation results and the earthquake is discussed. The conclusions are:① The first wavelet transformation results reflect the shallow layer material density variation in the earth from 1992 to 1993, from 1993 to 1994 and from 1994 to 1995, and there are anomalous gravity varia-tions near the earthquake area before the earthquake. Especially. the gravity variation is very clear during the earthquake from 1995 to 1996.② Although the second and third wavelet transforma-tion results of gravity variation according with the deep layer material density change of the earth have some variations during the earthquake, they are all not obvious The reason may be that the Lijiang M_s7.0 earthquake occurred in the shallow layer of the earth crust (10 km).

Abstract:A better method is put forward to evaluate the inherent quality of observed earth resistivity data. The method comprehensively embodies a function of manifold factors such as equipment ac-curacy, environmental disturbance, seasonal variation, signal to noise ratio, ect.

Abstract:Based on the reports about investigation and disaster evaluation of the Gonghe M_s7.0 earth-quake and its strong aftershocks, the direct damages of these earthquakes are systematically summed up, the distribution regularity of earthquake damages is studied and their causas are anal-ysed There is the cause of human action besides geological reason. Only following natural law can we rebuid our homeland better.

Abstract:The genetic algorithm is applied to seismic location, and its results are compared with those of Powell algorithm and traditional algorithm. It is shown that when genetic algorithm is used, the precision of determined origin time is higher and the determined depth is more reliable. This method is better when the stations concentrate on one side of an earthquake.

Abstract:A Phase-matched filter is applied to extract phase of fundamental surface wave, and then time-variable filter is used to correct amplitude spectrum in order to isolate fundamental mode signs. By processing of synthetic seismogram of surface wave, it is shown that the method can pre-cisely isolate fundamental surface wave from higher synthetic seismogram including the fifth mode, and deformation of amplitude spectrum is very small comparing with spectrum of funda-mental mode resulted from the same model. Based on long period surface wave recording of the Chinese Digital Seismological Network, the fundamental mode is isolated from Rayleigh wave recorded at Beijing and Hailaer stations which is posisioned on the same great circle path with epi-center, the interstation Green's function is estimated from deconvolution of the fundamental mode signs of the two stations. The interstation group velocity and attenuation in a period of from 13 seconds to 140 seconds are calculated from the Green's function, moreover, the results are signifi-cantly more stable.

Abstract:By inversion of travel-time data of S_n waves from natural earthquakes recorded by local seis-mic network in Shaanxi Province and adjacent areas, the velocity image of Moho discontinuity be-neath the Weihe fault depression and adjacent areas is obtained. Then stability of the used method and reliability of the results are discussed.

Abstract:Based on the data of geophysical prospecting and geochemical exporation ahout the north and south central faults in the Qaidam basin, structure activity characteristics of the faults and risk of earthquakes occurring along the faults in the future are analyzed and displacements caused Ly the future earthquakes with upper limit magnitudes are approximately estimated for reference of archi-tectural designers.

Abstract:Based on well water level b-valve dynamics in the Jiyang depress on and strikes of faults on which the wells exist, directions of principal stresses before strong earthquakes in North China are inferred and their evolution laws among different fault blocks are preliminarily summed up in or-der to add a new method for earthquake prediction by using subsurface fluid.

Abstract:The Shuiquanjianshan-Juewushan south piedmont fault zone in Jingyuan region, Gansu Province was a strike reverse fault before early Quaternary and became sinistral strike-slip fault in middle Quaternary. As the strong activity occurred along the Haiyuan fault zone, the activities of the Shuiquanjianshan-Juewushan fault zone, other active faults before late Quaternary and com-pressive settling basin within the region were stopped.Obviously, activity of the Quaternary fault was characterized by lateral migration. It is considered that the migration mainly resulted from change of principal stress orientation of regional stress field and characteristic structure boundary condition.

Abstract:The effects of overburden thickness and topography on earthquake ground motion are ana-lyzed in accordance with the particularity of loessial sites. An experiential method of evaluating ef-fects of overburden thickness and topography on ground motion is proposed based on a lot of sta-tistical data of seismic response of sites, which can serve as the basis for preventing and reducing the loessial disasters caused by earthquakes.

Abstract:A method to process daily observation data at seismostation is introduced. Through Visual Basic programme, the data curves are made by printer. the printer is more effective than plotter. and a simple example is presented.

Abstract:The elastic constant is a component of a three-dimensional fourth-rank tensor, hav-ing 81 components, in all. According to the symmetry of both the stress and strain ten-sors and the existence of a density energy function, which is quadratic in strain, the number of independent constants is 21 for general anisotropic media. The number of in-dependent elastic constants can be reduced still mord if media have higher symmetry. Transversely isotropic medium, which has only five indepindent constants, is a good ap-proximation of rocks in the crust and the upper mantle of the earth.In this paper, we are concerned about transversely isotropic media with an arbitiary direction of symmetrical axis(i.e., the symmetrical axis may not be parallel to the verticalaxis). In this case we need to change coordinates from one system to another. If we know the elastic constants in one particular coordinate system, for example, whose axes are parallel or perpendicular to the symmetrical axis of the midia, we can easily obtain these elastic constants in new coordinate system by using the transformation formula.
In this paper we present an approach for modeling wave-fields excited by not only a source but also a plane-wave incidence in transversely isotiopic media mentioned above by the pseudo-spectral method. Modeling of plane waves propagating in transversely isotropic media is one of the most important subjects as well as that of waves emitted from a localized source in exploration geophsics and seismology. While it is deffcult or even impossible to determine the phase velocity and the polarization direction of plane waves in general an anisotropic media, in the case of transversely isotropic media we can achieve this purpose through coordinate transformation. We here develop a scheme that can be used for plane-wave modeling in travsversely isotropic media,