Quick identification of multilevel similar earthquakes using hierarchical clustering method and its application to Wenchuan northeast aftershock sequence

Similar earthquakes are a group of earthquakes which have highly similar waveform at one or more seismic stations,they always occur as clusters in a limited space.Repeating earthquakes,as distinguished similar earthquakes,have nearly identical focal mechanism and overlapped rupture area.They provide an important means for studying the structure and property variation of fault systems.Here we present a method,which is based on similarity distance matrix and hierarchical clustering algorithm,to perform multilevel quick identification of similar earthquakes by one single station.We apply this method to Wenchuan northeast aftershock sequence and obtain the spatial and time distribution of different level similar earthquakes.The ability for detecting repeating earthquakes as well as the possible mechanism of burst-type repeating earthquakes in this region are discussed in the end.