| Passive surface method using dense arrayed wireless seismograph are useful for 3D near surface S-wave velocity structure modeling.Conventional microtremor survey are utilized mainly 1D survey and rarely applied to 2D or 3D survey, because it takes a lot of manpower and time to acquire 3D data using conventional seismographs. However, a recently development of wireless seismograph make us to acquire 3D data with less manpower and time compare with using conventional seismographs.We applied a circularly arrayed passive surface method and acquired ambient noise using total 49 sensors. In this study it is demonstrated that phase velocities for frequency range from 1Hz to 7Hz can provide reasonable S-wave velocity structures down to 100m. The result shows inhomogeneous S-wave velocity structures, and this fact shows a dense arrayed passive surface method is high practicality.Also, we conducted 2D Linear Array Microtremor Survey Method (hereafter referred to as 2D-LAMS), and the Cone Penetration Test (hereafter referred to as CPT) at same site to complement 3D S-wave velocity model. 2 lines were deployed in a orthogonal direction, 24 seismograph and 2Hz geophones with 2.5 m geophone spacing were used along each line. The 2D-LAMS results shows more detailed S-wave velocity structure, the higher velocity structure lies between 10m to 20m depth, compared with the circularly arrayed passive surface method study.CPT, including Seismic CPT, was conducted at 3 points to obtain a geological profile of ground depthwise direction. In the CPT test, stiff sand layer that have higher S-wave velocity are seen from 10m to 20m depth, and the result of Seismic CPT test are consistent with the result of passive surface method and 2D-LAMS.These experiments verify a dense arrayed passive surface wave method, including 2D-LAMS are useful to create a 3D near surface S-wave velocity model with less labor and time. |
