A Discussion on Correlations of Plate Motion with Seismic Anisotropy and Stress Field in Plate Boundary Zones

In many parts of the global plates,including subduction zones,mid-ocean ridges and even the interior of the continental plates,seismic anisotropy has a certain correlation with image of absolute plate motion( APM),or is in accord with the predominant direction of the intraplate stress field. In our study,a statistical analysis is done on the correlations of plate motion with seismic anisotropy as well as a stress field within nine plate boundaries which contain major subduction zones in the globe. Results indicate that absolute or relative plate motion( RPM) controls the seismic anisotropy and stress field of the plate boundary,which is especially obvious for the RPM. It can also be inferred that the correlation of RPM is better than that of APM. Because of the complexity of subduction mechanism and diversity of controlling factors at plate boundaries containing subduction zones,the correlation becomes much complex. Sources of anisotropy at various depths show different characteristics,and stress state is controlled by many factors,thus further discussions on the correlations are required.

Research on the correlation between North China earthquake and global regional strong earthquakes

Active belts of global strong earthquakes were divided into 17 seismic zones based on the principles of global plate tectonics.The seismicity index number A(b) was used to denote the yearly seismicity level.Using the stepwise regression method,an empirical formula was derived to predict the North China seismic risk in the next year by the aid of strong earthquakes in the world.

Analysis of the relationship between water level fluctuation and seismicity in the Three Gorges Reservoir(China)

The Three Gorges Reservoir is a good site for the further researches on reservoir induced seismicity due to decades＇ seismic monitoring. After the first water impounding in 2003, seismic activity becomes more frequent than that before water impoundment. In order to quantitatively study, the relationship between the water level fluctuation and earthquakes in TGR, we introduced statistical methods to attain the goal. First of all, we relocated the earthquakes in TGR region with double difference method and divided the earthquakes into 5 clusters with clustering analysis method. Secondly, to examine the impacts of water level fluctuation in different water filling stages on the seismic activity in the 5 clusters, a series of statistical analyses are applied. Pearson correlation results show that only the 175 m water level fluc- tuation has significantly positive impacts on the seismic activity in clusters I, II, III and V with correlation coefficients of 0.44, 0.38, 0.66 and 0.63. Cross-correlation analysis demonstrates that 0, ], 0 and 0 month time delay separately for the clusters I, II, III and V exists. It illustrated the influences of the water loading and pore pressure diffusion on induced earthquakes. Cointegration tests and impulse response analysis denoted that the 175 m water level only had long term and significant effects just on the seismic events in the intersection region of the Fairy Mount Fault and Nine-brook Fault. One standard deviation shock to 175 m water level increased the seismic activity in cluster V for the first 3 months, and then the negative influence was shown. After 7 months, the negative impulse response becomes stable. The long-term effect of the 175 m water impoundment also proved the important role of pore pressure diffusion in RIS with time.

Growing correlation length of moderate-sized earthquakes prior to two great earthquakes near Sumatra Island

Seismic correlation length for moderate earthquakes prior to two great earthquakes in the northern sea area of Sumatra Island （Mw9.1 in 2004 and MsS. 6 in 2012） has been studied, using method of Single- Link-Cluster （ SLC ） analysis, and found to show a power-law growth about two years before their occurrences. No such growth was found for a magnitude 7 earthquake in the same area. This result suggests the occurrence of a physical process of critical-point characteristics in the source area before the great earthquakes.

Large scale characteristic distance between strong earthquake

The global seismicity shows a characteristic distance of about 23°. The middle deep and deep earthquakes in the European and Asian blocks concentrate on several zones which separate about 23° away from earch other. The shallow strong earthquakes ( M S≥7) form belts of over 20°, the ends of these belts are near the concentration points of middle deep and deep earthuakes. The Circular Pacific island arcs, volcanoes, shallow earthquakes, middle deep and deep earthquakes also show the characteristic distance of about 23°.