On The Identification Analysis And Research Of Impending Earthquake Anomaly Characteristics

Earthquake is some parts of the earth's crust under the action of long-term tectonic force,energy after long-term accumulation and sudden release of the formation.Therefore,the occurrence and propagation of pre-earthquake disturbance are relatively related to the change of underground stress,which contains the physical information such as structure,stress state,mechanical parameters of medium and dynamic response of non-uniform medium to the main fracture surface,and also reveals the mechanical process of fault current motion,earthquake incubation process and earthquake precursors.In this paper,based on the previous studies on the earthquake itself,the preseismic disturbance of the relevant earthquake is further studied by using the broadband seismograph in Sichuan.Because giant earthquake of wenchuan earthquake interval for about 5 years and seismogenic in longmenshan fault zone,this article selected the broadband seismograph in sichuan earthquake networks center before the wenchuan earthquake on May 12,2008,12 days and 10 days before the giant earthquake in 2013 consecutive waveform records,the wavelet and spectrum characteristics analysis,the results showed that:(1)The disturbance characteristics before the 2008 MS8.0 Wenchuan earthquake:Look from the waveform data in 3 ? 4 days before the earthquake there was evident abnormal disturbances-amplitude increases gradually,from the point of view of frequency domain abnormal low frequency disturbance signal frequency range of 0.18? 0.25 Hz and 0.1 ? 0.18 Hz,concluded after analysis of main frequency of 0.18 ?0.25 Hz signal is mainly influenced by the western Pacific typhoon Rummasun,the abnormal signal began in May 9,and at the end of the 11 th,12th early near maximum intensity,after with the storm center away from the mainland and a significant attenuation;However,the anomaly in the frequency band of 0.1-0.18 Hz gradually increased from about May 10 and increased sharply 10 h before the earthquake,which was relatively related to the earthquake.(2)Spectrum characteristics before the MS7.0 Ya 'an earthquake in 2013: there was no significant increase in the amplitude of continuous waveform recorded by all stations within 10 days before the earthquake,and no low-frequency disturbance signal appeared in the frequency domain.According to the spectrum peak curve,in the frequency domain,the disturbance signal with the main frequency of 0.2?0.25 Hz showed a slight downward trend in the 10 days before the earthquake,but it was not obvious.The wavelet time-frequency diagram also shows the weakening of the signal in the low-frequency band,but the MDS and EMS stations close to the epicenter of Ya'an found an increase several hours before the earthquake,which is different from other stations.(3)By comparing Wenchuan earthquake with Ya 'an earthquake,it is found that the increase of the non-typhoon frequency band of 0.1-0.18 Hz before Wenchuan earthquake,the slight decline of the frequency band of 0.2-0.25 Hz before Ya 'an earthquake and the intensity increase of a few stations near the epicenter probably reflect the slow dislocation occurred before the rupture of the fault zone.Ya 'an earthquake is pure thrust dislocation,the initial rupture point is deep,the rupture time is short,and there is no obvious direction,the surface did not produce a large rupture surface,which is the most different from Wenchuan earthquake,so the two pre-earthquake disturbance phenomenon is likely to be related to this,which needs to be tested by more earthquake cases.