| We created a 3D S-wave velocity structure model by mean of passivesurface survey up to 100 m depth. Cableless seismographs (ATOMR) were deployed on a 2D quadplexconcentric array to form isotropic alignment to ambient microtremors. The concentric seismograph arraywas set in a 200 m diameter test circuit road situated in PWRI Tsukuba site, central Japan. In addition to theconcentric array survey, we conducted Hybrid or walk-along surface wave surveys along 5 linear surveylines, cone penetration tests (CPTs) at 2 points, and a VSP at one point all of which were located inside thecircuit. A total 20 hours data were recorded by using the concentric array composed of 49 cablelessseismographs as the passive seismic survey. It took only 3 hours to deploy seismographs to theprepositioned points and additional 2 hours for retrieving seismographs after the measurement by a taskforce with 3 members.3D velocity structure reconstructed from the passive surface wave survey clearlyimaged a distinct velocity increase at 40 to 45 m in depth, which was concordant with existing geotechnicalboring data.Our field test demonstrated that we could make a 3D S- wave velocity structure model of a siteof interest with a smaller task force and lighter field works compared with conventional methods. Moreover,we demonstrated the effectiveness of integrated geophysical survey, composed of 2D Hybrid surface wavemethod (HSWS) and 1D CPT and VSP, for increasing reliability of the 3D model we created. |
