In the paper, we analyze 117 moderate-strong earthquakes occurred in Chinese mainland (M S≥5.5 in the east and M S≥6.0 in the west) since 1970, among them, 11 earthquakes (about 9%) have direct foreshocks and 63 earthquakes (about 51%) have generalized foreshocks. The predominant time interval between foreshock and main earthquake is no more than 30 days with a spatial distance less than 50 km and a magnitude difference over 1. From the digital seismic data in liaoning Province, we know that direct foreshock had an obvious shear-stress background before the M S=5.6 and M S=5.1 Xiuyan earthquakes occurred on Nov. 29, 1999 and Jan.15, 2000.

Though the forecast and prediction of earthquakes is a commonly accepted difficult problem in science, the step towards the exploration and knowledge of the generation and occurrence of earthquakes has never stopped. It has strong scientific exploration nature and great social efficacy in disaster reduction. For this reason, it has always been the object and motivation pursued assiduously by earthquake researchers. It is beyond doubt that the study of seismicity is still one of the important information sources that have historical records of the longest time and most abundant earthquake cases that can be testified. For many years, with the progress of study in this aspect and the unceasing increase of study methods, there have been not less than tens of methods that can be used to describe theseismicity characteristics from different angles. It is of great importance to determine from the numerous methods those ones that are relatively independent and to understand how many dimensions are there to restrict the complexsystem of earthquake generation and occurrence. Taking these as a referential basis, we would be able to identify the quantities that restrict the study of the seismogenic system, to raise the scientific value and rigorousness of prediction and forecast, and to get rid of the trouble of repeated information superposition.

Improvement of pulse amperometric detection (PAD) method is demonstrated in determination of ethylenethiourea (imidazolidine-2-thione, ETU). The anodic detection of ETU will produce polymeric film on an electrode leading to an inactive electrode surface. Here, the PAD method was used to remove the polymeric film formed on the electrode surface between ETU detection. Further, the scheme was integrated with automated flow injection analysis (AFIA) for determining ETU. The operational parameters of PAD in the AFIA system were discussed thoroughly. The analytical characteristics of the system were evaluated at optimum conditions. The linear range of calibration plot was between 20 to 300 muM (the correlative coefficient, r = 0.999) and the detection limit was 0.9 muM (S/N = 3). The relative standard deviations of detection of 50 muM ETU were 0.82% with and 9.07% without PAD scheme. The results indicate the system is a very promising toot for ETU determination. Finally, the matrix effects of two water samples that were collected from a campus and a farm show good recoveries of 92% and 96%.

Based on the analysis on the characteristics of spatial image variation of medium and small seismicity prior to M_S 6 earthquakes occurred in North China area since 1970, the space-time characteristics and the background for the occurrence of are studied. According to the characteristics of field-source relation, a strict selection and recognition is made for the earthquakes and the relevant prediction index for the signal shocks are obtained. Generally speaking, the signal shocks occur in 2 years prior to the strong earthquake and most of them occur within 15 months; the distance between the signal shock and the strong earthquakes is no larger than 200 km and most of them are within 100km; the magnitude of the signal shocks is usually about M_L4.0～5.3. The signal shocks generally occur in the M_L4.0 seismically quiet area of a certain region, which occur in or near the medium and small seismic stripes with the seismicity gap of medium and small earthquakes nearby. The testing results indicate that in 9 months after the signal shock, its predictive probability is 0.5 and its R value is 0.27; when the radius of the predicted region is within 100 km to the epicenter of signal shocks, the probability for the occurrence of the predicted earthquakes is 0.73 and the predicted magnitude is generally M_S 6.0. The study in the paper indicates that the environmental stress value τ_0 of the signal shock is obviously higher than that of other earthquakes, which shows the significant abnormal background of high stress. Its seismic waves might probably contain a great amount of essential information of the seismogenic zone for the coming strong earthquakes.

The effective utilization of industrially waste cinder for electroanalytical applications by trapping the hexacyanometallate (HCF) units from Fe3+, Ni2+, Co3+, etc into the interlayer galleries of cinder has been reported. Prussian blue (PB) is an Fe(III)-HCF with mixed valence and zeolite type properties. In the present investigation, the intercalation property of Tl+ with PB/cinder paste electrode (designated as PBCPE) has been utilized for the analytical purpose. Basic cyclic voltammetric experiments with Tl+ in 0.1 M KNO3 results in a continuous insertion of Tl+ ions inside the PB gallery with the ejection of K+ ions. The insertion rate of Tl+ ions in the PBCPE was much faster as compared to that in traditional PB-modified electrodes. The PBCPE has also been utilized for sensitive determination of Tl+ ions in real samples.

In this paper, the relation that the curves of nonlinear parameter H and its difference ΔH bear with strong earthquakes in North China has been studied. First, the RSH algorithm has been applied to the North China region; the schemes of six quantitative prediction indexes have been studied in detail and then tested by tracing-back predictions. The result shows that all the six prediction schemes are of certain prediction efficiency and have passed the test. Among the six schemes, A and E are of the best effect, with correlation coefficients R of 0.47 and 0.48 respectively. We recommend these two schemes for practical use in prediction in the future. Furthermore, the relation between the curve of ΔH (the difference of H) and strong earthquake has been studied. Based on the above results, the RSΔH algorithm that uses the ΔH value to predict strong earthquake has been put forward and applied to predict strong earthquakes in North China. The correlation coefficient R of tracing-back prediction by this method is 0.45; this means that this method is also of better prediction efficiency. A combined application of these two algorithms has also been proposed. By the combined method, the time length spanned by false predictions can be shortened and thus the R value can be raised.

The preliminary result of this work was obtained in 1992. At Consulting Meeting for Seismic Trends of China in Jan. 1993, we handed in a report and predicted that “Until now, the average magnitude curve\(\bar M\) haven’t gotten risen again after a fall, and the value ofH is under 0.4, so no alarm is made by each of these two. We predicted that, seismicity of the Chinese mainland in 1993 may be at the same level as in 1991–1992, or a little higher than it, but mustn’t be very high; this is to say that no earthquake withM s⩾7.2 will occur in the Chinese mainland in 1993.”