Using 1 Hz sampling records at one superconducting gravimeter （SG） station and 11 broadband seismometer stations, we found anomalous signals prior to the 2008 Wenchuan （汶川） earthquake event. The tides are remove...Using 1 Hz sampling records at one superconducting gravimeter （SG） station and 11 broadband seismometer stations, we found anomalous signals prior to the 2008 Wenchuan （汶川） earthquake event. The tides are removed from the original SG records to obtain the gravity residuals. Applying the Hilbert-Huang transform （HHT） and the wavelet analysis to the SG gravity residuals leads to time-frequency spectra, which suggests that there is an anomalous signal series around 39 h prior to the event. The period and the magnitude of the anomalous signal series are about 8 s and 3×10^-8 m/s^2 （3 μGal）, respectively. In another aspect, applying HHT analysis technique to 11 records at broadband seismometer stations shows that most of them contain anomalous signals prior to the Wenchuan event, and the marginal spectra of 8 inland stations show an apparent characteristic of double peaks in anomalous days compared to the only one peak of the marginal spectra in quiet days. Preliminary investigations suggest that the anomalous signals prior to the earthquake are closely related to the low-frequency earthquake （LFE）. We concluded that the SG data as well as the broadband seismometers records might be significant information sources in detecting the anomalous signals prior to large earthquakes.展开更多
The Hilbert-Huang transform （HHT） is used to analyze the time series from nine gravimeter （SG） stations and 22 broadband seismometers to investigate the anomalous signals superconducting prior to the great 2010 Ma...The Hilbert-Huang transform （HHT） is used to analyze the time series from nine gravimeter （SG） stations and 22 broadband seismometers to investigate the anomalous signals superconducting prior to the great 2010 Maule earthquake. The results show that seven SG time series and 20 broadband seismometer time series have anomalous signals lasting about one to three days before the earthquake occurrence. The anomalous signals appear around the frequency bands 0.07Hz and 0.15Hz in SG records while around the frequency band 0. 13Hz -0.2Hz in seismic records, and the reason why they appear in different bands might be attributed to the intrinsic nature and different sensitivities of different kinds of instruments. Because more than 87% records have the anomalous signals prior to the earthquake, and no typhoon event is found in our chosen time window, we may conclude that the anomalous signals might be precursory signals of the great 2010 Maule event. However, we do not rule out other possible excitation sources.展开更多
基金supported by the National Natural Science Foundation of China (Nos. 40974015, 40637034)the Research Program for Outstanding Doctoral Candidates of Wuhan University (No. 2008-50)
文摘Using 1 Hz sampling records at one superconducting gravimeter （SG） station and 11 broadband seismometer stations, we found anomalous signals prior to the 2008 Wenchuan （汶川） earthquake event. The tides are removed from the original SG records to obtain the gravity residuals. Applying the Hilbert-Huang transform （HHT） and the wavelet analysis to the SG gravity residuals leads to time-frequency spectra, which suggests that there is an anomalous signal series around 39 h prior to the event. The period and the magnitude of the anomalous signal series are about 8 s and 3×10^-8 m/s^2 （3 μGal）, respectively. In another aspect, applying HHT analysis technique to 11 records at broadband seismometer stations shows that most of them contain anomalous signals prior to the Wenchuan event, and the marginal spectra of 8 inland stations show an apparent characteristic of double peaks in anomalous days compared to the only one peak of the marginal spectra in quiet days. Preliminary investigations suggest that the anomalous signals prior to the earthquake are closely related to the low-frequency earthquake （LFE）. We concluded that the SG data as well as the broadband seismometers records might be significant information sources in detecting the anomalous signals prior to large earthquakes.
基金supported by the National Natural Science Foundation of China(41174011,41128003,41021061,40974015)National l973 Project(2013CB733305)the Fundamental Research Funds for the Central Universities(2012214020203)
文摘The Hilbert-Huang transform （HHT） is used to analyze the time series from nine gravimeter （SG） stations and 22 broadband seismometers to investigate the anomalous signals superconducting prior to the great 2010 Maule earthquake. The results show that seven SG time series and 20 broadband seismometer time series have anomalous signals lasting about one to three days before the earthquake occurrence. The anomalous signals appear around the frequency bands 0.07Hz and 0.15Hz in SG records while around the frequency band 0. 13Hz -0.2Hz in seismic records, and the reason why they appear in different bands might be attributed to the intrinsic nature and different sensitivities of different kinds of instruments. Because more than 87% records have the anomalous signals prior to the earthquake, and no typhoon event is found in our chosen time window, we may conclude that the anomalous signals might be precursory signals of the great 2010 Maule event. However, we do not rule out other possible excitation sources.
