Earth Planets Space, Vol. 60 (No. 10), pp. 1069-1074, 2008LETTER
Shiro Ohmi1, Kazuro Hirahara2, Hiroo Wada3, and Kiyoshi Ito4
1Earthquake Hazards Division, Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji 611-0011, Japan
2Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
3Kamitakara Observatory, Disaster Prevention Research Institute, Kyoto University, Takayama, Gifu 506-1317, Japan
4Research Center for Earthquake Prediction, Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji 611-0011, Japan
(Received July 14, 2007; Revised November 21, 2007; Accepted December 6, 2007; Online published November 7, 2008)
The passive image interferometry technique is applied to the continuous seismic waveform data obtained around the source region of the 2007 Noto Hanto Earthquake, central Japan. We computed the autocorrelation function (ACF) of band-pass filtered seismic noise portion recorded with each short-period seismometer at several seismic stations for 1 day each. In some stations, comparison of each 1-day ACF shows temporal evolutions of the ACF, which are interpreted as the change of seismic velocity structure in the volume considered. Sudden changes of ACF are detected to be associated with the occurrence of the main shock in one station of the four stations analyzed. Gradual changes of ACFs in the preceding 2 weeks of the main shock are also recognized in two stations, which would be of great importance for understanding the stress state before the occurrence of earthquakes.
Key words: Noto Hanto Earthquake, seismic interferometry, back ground noise, autocorrelation function.