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26 earthquakes with MS ≥5. 0 have been recorded in the northeast margin of the Qinghai- Xizang (Tibet) block since 1980,22 of which were relatively independent of other moderate- strong earthquakes. Research on the increase of small earthquake activity before the 22 moderate-strong earthquakes has indicated that small earthquake activity was enhanced before 17 of the moderate-strong earthquakes. Though the increased seismicity is a common phenomenon in the northeast margin of the Qinghai-Xizang ( Tibet ) block,we have difficulty in predicting the moderate-strong earthquakes by this phenomenon. In order to predict the moderate-strong earthquakes through the increased seismicity of small earthquakes,this paper attempts to propose a new method, which calculates small earthquake frequency through the change of distribution pattern of small earthquakes, based on the characteristics of small earthquake activity in the northeastern Qinghai-Xizang (Tibet) block,and then make primary applications. The result shows that we are able to obtain obvious anomalies in the frequency of small earthquakes before moderate strong earthquakes through the new method,with little spatial range effect on the amplitude of this small earthquake frequency anomaly. We can obtain mid to short-term anomaly indices for moderate-strong earthquakes in the northeast margin of the Qinghai-Xizang (Tibet) block.
26 earthquakes with MS ≥5. 0 have been recorded in the northeast margin of the Qinghai- Xizang (Tibet) block since 1980, 22 of which were relatively independent of other moderately strong earthquakes. Research on the increase of small earthquake activity before the 22 moderate-strong earthquakes has indicated that small earthquake activity was enhanced before 17 of the moderate-strong earthquakes. Though the increased seismicity is a common phenomenon in the northeast margin of the Qinghai-Xizang (Tibet) block, we have difficulty in predicting the Moderate-strong earthquakes by this phenomenon. In order to predict the moderate-strong earthquakes through the increased seismicity of small earthquakes, this paper attempts to propose a new method, which calculates small earthquake frequency through the change of distribution pattern of small earthquakes, based on the characteristics of small earthquake activity in the northeastern Qinghai-Xizang (Tibet) block, and then make primary application ions. The result shows that we are able to obtain obvious anomalies in the frequency of small earthquakes before moderate strong earthquakes through the new method, with little spatial range effect on the amplitude of this small earthquake frequency anomaly. We can obtain mid to short- term anomaly indices for moderate-strong earthquakes in the northeast margin of the Qinghai-Xizang (Tibet) block.