The Quantitative Identification of Regional Mine and Natural Earthquakes and Its Application

Based on the Morlet wavelet transform and digital data from the Fushun and Beizhen seismic stations, Liaoning Province, we put forward a new method in the paper, called time-frequency energy attenuation factor （α-value）. The characteristics of the α-value and its variation with magnitude of natural and mine earthquakes are studied, and the statistic relations between the α-value and specific earthquake magnitude are obtained. From the results, some conclusions can be drawn as follows： （1） in general, the α-values of mine and natural earthquakes of the same intensity have obvious difference and the ranges of their variation do not overlap each other; （2） the α-value decreases with the increase of earthquake magnitude, and the α-value of mine earthquake decreases faster than that of natural earthquake; （3） based on the earthquake magnitude and on the relations between the α-value and earthquake magnitude, we can distinguish the mine earthquakes from the natural ones; （4） the difference in focal mechanism of mine and natural earthquakes would be the main cause for obvious difference of the α-value; （5） the α-value variation is relatively steady for mine and natural earthquakes that occur in the same region, but it has obvious regional difference. The above results are of inspirational meaning for the study of abnormal change of the α-value before strong earthquakes.

Identifying the occurrence time of an impending mainshock:a very recent case

The procedure by means of which the occurrence time of an impending mainshock can be identified by analyzing in natural time the seismicity in the candidate area subsequent to the recording of a precursory seismic electric signals（SES） activity is reviewed. Here, we report the application of this procedure to an MW5.4 mainshock that occurred in Greece on 17 November 2014. This mainshock（which is pretty rare since it is the strongest in that area for more than half a century） was preceded by an SES activity recorded on 27 July 2014, and the results of the natural time analysis reveal that the system approached the critical point（mainshock occurrence） early in the morning on 15 November 2014.

Frequency band-dependence of S-wave splitting in China mainland and its implications

Butterworth band-pass filter has been applied to S-wave data recorded at 8 stations in China mainland, and S-wave splitting at different frequency bands is analyzed. The results show that the delay time and the fast polarization directions of S-wave splitting depend upon the frequency bands. There is an absence of S-wave splitting at the station of Urumqi (WMQ) for the band of 0.1-0.2 Hz. With the frequency band broadening, the delay time of S-wave splitting decreases at the stations of Beijing (BJI), Enshi (ENH), Kunming (KMI) and Mudanjiang (MDJ); the fast polarization direction changes from westward to eastward at Enshi (ENH), and from eastward to westward at Hailaer (HIA). The variations of delay time with bands at Lanzhou (LZH) and Qiongzhong (QIZ) are similar, and there is a coherent trend of fast polarization directions at BJI, KMI and MDJ, respectively. Initial interpretations to the results of frequency band-dependence of S-wave splitting are also presented.