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| | Abstract | | To develop non-invasive methods for levee inspection, geophysical investigations were carried out at three sites along levees in New Orleans. The sites sustained damage from Hurricane Katrina in 2005 and have since been rebuilt. The geophysical methods include active and passive surface wave methods, and capacitively coupled resistivity. This paper mainly summarizes the acquisition and analysis of 2D passive surface wave data. Twelve cableless seismic data acquisition units with 2 Hz vertical component geophones were used to record data. Each unit includes a GPS receiver so that all units can be synchronized over any distance without cables. Data acquisition used linear arrays with a geophone spacing of 5m. Four geophones were moved forward every 10 minutes along 450 ~ 1,100 m length lines. Data acquisition took several hours for each line. Recorded ambient noise was processed using spatial autocorrelation and clear dispersion curves were obtained at all sites. Minimum and maximum frequencies ranged from 1 to 2 Hz and from 9 to 30 Hz respectively depending on the site. Non-linear inversion yielded 2D cross sections along the levees penetrating to a depth of 40 ~ 60 m. Resultant S-wave velocity models are generally consistent with existing drilling logs and laboratory tests. |
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