Source location method of microseisms with double seismic phases based on TFA-DC arrival time picking

Aiming at the difficulty of picking up the first arrival time of S wave in double seismic phases location, the double seismic phases location method (the TD-DL method) is proposed, which uses both the accurate arrival time of P wave and the peak arrival time of S wave obtained by the time frequency analysis downhill comparison method (the TFA-DC method). The objective function of double seismic phases is introduced to calculate the estimated value of earthquake occurrence time, and the wave velocity of double seismic phases is integrated into the propagation velocity of seismic phases, which is used as the unknown variables together with the source coordinates in the particle swarm optimization algorithm for calculation. The TD-DL method is composed of the method above and the TFA-DC method. Using the characteristics of the TFA-DC method to pick up P wave arrival time and S wave arrival time, combined with the positioning results of two kinds of single seismic phase and the TD-DL method under model test, the differences and relations between single seismic phase and double seismic phases positioning are obtained, and the principle of improving positioning accuracy by this method is demonstrated. By comparing the advantages and disadvantages of two kinds of single seismic phase and the TD-DL method in positioning accuracy and stability, the superiority of the method is verified. The results show that due to the increase of constraint information of S wave arrival time and the trend of minimum value of objective function, the TD-DL method improves the integration ability of known information such as geophone coordinates and arrival time of double seismic phases, and makes the positioning results tend to the one with smaller error than the real source positioning results of two kinds of single seismic phase, to a certain extent. The positioning error of P wave and S wave single seismic phase calculation is offset, thus the positioning accuracy of source inversion is improved. Under the model test, the average positioning error of the TD-DL method is 23.9% and 18.9% of P wave and S wave single seismic phase positioning respectively, and the standard deviation of positioning error is 50.9% and 36.9% of P wave and S wave respectively. Under the engineering data, the average positioning error of the TD-DL method is 8.1% and 12.6% of P wave and S wave single seismic phase positioning respectively. There is a negative correlation between the number of coordinate changeable geophones on each coordinate axis and the error of positioning results on the corresponding coordinate axis. The requirement of high density geophones for high precision positioning can be simplified as the high density geophones on the corresponding free surface of each axis.