Seismological investigations of two massive explosions in Tianjin, China

In this study, we analyze available weak- and strong-motion seismograms to discern the main source characteristics of the 12 August 2015 Tianjin explosions. The disaster involved two large explosions, which can be clearly identified in the near-field seismic recordings. The first explosion (event 1) took place at 15:34:04.68 (UTC) and the second at 15:34:36.94 (UTC). The average time interval between the two events was about 32.3 s, which is consistent with the result determined by cross correlation of the whispering gallery wave (WG phase). The two events did not occur at the same site, and the second explosion was located 65±10 m northwest (N352°W) of the first one. The local magnitudes M_L of the two explosions were further measured as 2.4 and 2.9, respectively. The Fourier spectra from the two closest stations, DAG and BET, show that the predominant frequency of the waveforms ranged from 0.7 to 0.9 Hz after the long-period wavetrains had arrived. According to the distribution of the three-component peak ground acceleration, the area with a shaking intensity of modified Mercalli intensity VI spanned up to 131 km². However, the peak intensity of this explosion did not reach an intensity of VII, based on the ground-motion attenuation relation.