Vol.9 No.2 2016

Research paper : Constructing a system to explore shallow velocity structures using a miniature microtremor array (I. CHO et al.)−95−Synthesiology - English edition Vol.9 No.2 (2016) this as an example. This is the S-wave velocity cross-section obtained when we had geology researchers (non-experts of microtremor exploration), who wished to evaluate the subsurface velocity structure of the grounds of Urayasu High School in Chiba Prefecture to study the liquefaction phenomenon, use the new system in a trial. This result was used in a conference presentation by Sato et al.[29] After receiving a simple lecture on miniature array measurement, the researchers drew two measurement lines of 40 m and 120 m on the grounds of the high school, and repeated miniature array measurement at about 5 m intervals. About 20 min were spent per point, or a total of 12 hours. However, the total measurement time for the shorter measurement line was less than 2 hours.Since the data transfer system (Section 4.2.2) and the analysis result delivery (Section 4.2.3) were incomplete, we received the measurement data when the equipment was returned. Figure 7 shows the complete automated process from data analysis to drawing for the 120 m measurement line. From the survey for the landfill work of 1965-1971 as well as from hand-operated auger boring,Term 2 it is known that the topmost part of the grounds of Urayasu High School is 3 m of landfill layer that is composed of a sand layer and a silt layer in the east and west of the center of the measurement line.[30] In the part up to 10 m of depth of the velocity cross-section in the figure, clear difference is shown at about 45 m horizontal axis.5 In the futureWe believe about 70 % of our goal has been completed. It is necessary to work on the components that have not been addressed (data transfer system and analysis result delivery) and parts that can be refined (such as an estimation method for ground structures).Currently, there is a plan for measurement using miniature arrays at 1 to 2 km grid for the entire Kanto Plain area, and it has been partially conducted.[30] We wish to utilize this data to discern the limitations and possibilities of the new system and to consider future development.The research group to which Cho, one of the authors, belongs is working on the high resolution geological ground maps.[31] We are considering the application of this new system and adding the quantitative evaluation using the microtremor data.TerminologiesTerm 1.S-waves: A type of seismic wave. The seismic waves that travel through materials internally are called body waves, and they can be separated into P- and S-waves according to the relationship of directions of propagation and particle motion. The seismic waves that travel on material surfaces are called surface waves, and can be separated into Rayleigh and Love waves according to the relationship of directions of propagation and particle motion.Term 2.Logging: Measurement of the subsurface geology and ground conditions using boreholes. Boring is the term used for the act of digging a cylindrical hole in the ground or for the hole itself. Hand-operated auger boring is boring using hand drills.Term 3.Artificial seismic source: Vibrations caused by explosion, pounding, or a vibrator (truck-mounted device) that are instigated near the surface to artificially generate seismic waves. The exploration Fig. 7 S-wave velocity cross-section by miniature array exploration conducted on the Urayasu High School groundsThe right and left part of the cross-section diagram corresponds to the south-east and north-west directions, respectively. The legend of the cross-section shows the S-wave velocity with unit m/s. The triangles in the cross-section diagram show the positions of miniature arrays, and the dashed lines show the range of depth where the velocity structure data exist. Generic Mapping Tool[28] was used for drawing.20015010050-5-10-15-20-250510Distance (m)Elevation (m)S-wave velocity (m/s)0.0020406080100


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