Statistics Analysis of Anomalous Signals Prior to Large Earthquakes

Weihang Huang, Wen-Bin Shen, Wenqiang Zhang, Xiang Gu, Tianxing Jiang

Anomalous signals prior to large earthquakes might be detected based on superconducting gravimeters (SGs) and broadband seismometers (BSs) records. In this study, we selected 12 large earthquakes with their seismic magnitudes larger than 7.8, occurred between 2006 and 2010. Hilbert-Huang transform (HHT) technique, which is applicable for nonlinear and non-stationary processes, was applied to SG record and BS data sets sampled at one-second interval covering the time span 7 days prior to and 1 day after these earthquakes. Our study shows that anomalous signals are likely to occur in any one of the several days prior to large earthquakes. The results based on the SG record show that the anomalous signals with dominant frequency around 0.13 Hz occur 16 hours to 5 days prior to the large earthquake. Whereas records from 48 BS station suggest four obvious intrinsic frequency bands, namely around 0.06Hz, 0.33Hz, 0.43Hz and 0.46Hz, respectively. Concerning the BS records, the anomalous signals are characterized by total increase of the energy of signals and the anomalous peaks of the marginal spectra around 0.15-0.2 Hz and 0.33 Hz.