Abstract: The aim of the Blade algorithm is to search the seismic fault based on the distribu-tion of earthquakes. It can find stripe pattern from sparse epicenter distribution. But the com-plete ignorance of the most important attribute of earthquakes, and the seismic moment is itsobvious shortcoming. This paper improves the Blade algorithm step by step and develops theMs-weighted 4 index Blade algorithm. The main improvements of the Ms- weighted 4-indexBlade algorithm include:(1) The Ms-weighted function is introduced for showing thatstronger earthquakes have more effects on index. We compare the effects of three Ms- weight-ed functions through simulation and application.(2) The blades selected out by the Blade algo-rithm must have an earthquake as the center. This is disadvantage of accurate location of theblade results. The 4-index evaluation is instead of the 2-substituting index in the Blade algo-rithm so that the selected -out blades can be amended for more accurate position by the evalua-tion index and the evaluation is more efficient. The Blade algorit hm and the improved algo-rithms are applied to find the seismic belts based on the earthquakes(Ms>4. 0) in the NorthChina. The comparison of the results shows that the M s-weighted 4. -index Blade algorithm hasmore not able improvement than the Blade algorithm and obtains the satisfactory result.

Key words: Blade algorithm, Ms- weighted 4- index Blade algorithm, Seismic belt, NorthChina region