Abstract: A massive chemical explosion accident hit Tianjin Binhai on August 12, 2015, which caused serious casualties and property losses, and also caused a larger social repercussion. Tianjin seismic network center and China Earthquake Networks Center first reported in an official post on social media that there are two massive explosions, the first of which occurred at 11:34:04 (Beijing time) and only about 30s later another more powerful one occurred nearby, and the preliminary magnitude of these accidental explosions were estimated to be about M_L2.3 and M_L2.9 respectively. In this paper, we first indentified the properties of seismic phase with stronger energy based on the arrival time information and the trajectories of particles. And then detected whether there is other smaller explosion event except the two massive explosions using matched filter technique, and inspected the effects of detection method by 1000 times Bootstrap test. Further we estimated the relative position of two massive explosions using the differences of seismic phase arrival time information obtained from waveform cross-correlation phase detection.
   Seismic phase identification results show that the body wave seismic phase has the strongest energy recorded by regional seismic network may be the Pg phase which spread along the top of sediments. And the surface wave phase has the strongest energy recorded in vertical component may be the Rg phase. The first arrival seismic phase might be head wave phase spread along the crystalline basement. We detected two small suspected explosions, which occurred about 2 s before and 84 s after the first massive explosion, and their equivalent approximate to M_L0.5 earthquakes. The relocation result based on Pg phase arrival time differences shows that the second massive explosion is in the north west side of the first one, and the two explosions have about 50~55 m apart. According detailed seismology analysis of the explosion accident, we note that seismic network can play an important role in the process of accident emergency disposal. In the short time after the accident happened, when investigators cannot enter the explosion core region, analysis based on seismic waveform can help the government to understand the detailed process of explosion quickly and take timely and reasonable disposal method.

Key words: Matched filter technique, Relative relocation, Seismic phase identification, Massive explosions in Binhai, Tianjin