Shallow structure of Mozumi-Sukenobe fault zone imaged by simulation of fault zone waves generated by near-fault explosion experiments

Mamada, Yutaka*; Nishigami, Kinya*; Ito, Hisao*; Kuwahara, Yasuto*

The explosion experiments at the Mozumi-Siukenobe fault enabled us to collect high quality records using the linear seismometer array installed in an underground tunnel at a depth of 300 m. The seismograms contained high frequency components of up to 25 Hz. The phases interpreted as fault zone head waves, direct- waves propagating within the fault zone, and fault zone trapped waves were clearly found on the seismograms. Using such high quality records, we could perform fault zone wave modeling. We successfully simulated almost the characteristics on the observed seismograms with high frequency components of up to 25 Hz and revealed the complex structure of the Mozumi-Sukenobe fault zone terminating just east of the site SP1. This indicates the possibility of modeling for high frequency seismic waves that excited at the fault zone. According to this modeling, the precise -waves velocity adjacent to the fault zone and velocity contrast of waves between the wall rock and fault zone were estimated. The modeling also indicates the possibility of detecting fault zone discontinuity, in other words, the segmentation of fault at depth.