WORK PLANS - Laserfiche WebLink

Home Browse Search

Repeat for all shot records and merge dispersion curves Convert dispersion curves to WINSASW software package format for modeling An iterative forward modeling process was used to generate S-wave velocity models for each sounding. During this process an initial velocity model was generated based on general characteristics of the dispersion curve. The theoretical dispersion curve was then generated using the 2-D modeling algorithm (fundamental mode Rayleigh wave dispersion module) and compared to the field dispersion curve. Adjustments are then made to the thickness and velocities of each layer and the process repeated until an acceptable fit to the field data is obtained. 3.4 Interpretation of Seismic Refraction Results The seismic refraction model for SL-1 is presented as Figure 4. Two layers corresponding to unconsolidated fill / soils unit and more consolidated soils were modeled in the refraction data. The fill unit has modeled thicknesses between 10-14 ft and an average velocity between 1,100 and 1,250 ft/s. The more consolidated soils unit below is modeled as having an average P-wave velocity of 1,950 ft/s. The seismic refraction model for SL-2 is presented as Figure 5. Two layers corresponding to unconsolidated fill / soils and more consolidated soils were modeled in the refraction data. The fill unit has modeled thicknesses between 8.5-13 ft and an average velocity ranging between 1,100 and 1,350ft/s. The more consolidated soils unit below is modeled as having an average P- wave velocity of 2,100 ft/s. The seismic refraction model for SL-3 is presented as Figure 6. Two layers corresponding to unconsolidated fill / soils unit and more consolidated soils were modeled in the refraction data. The fill unit has modeled thicknesses between 8.5-15 ft and an average velocity between 1,100 and 1,200 ft/s. The more consolidated soils unit below is modeled as having an average P-wave velocity of 1,800 ft/s. The lower soils unit was not able to be mapped beneath the entirety of the seismic profile due to the limitations of far-offend shots by the fence immediately to the south. 3.5 Interpretation of MASW Results The fit of the theoretical surface wave dispersion curve to the experimental data collected along each MASW array and its corresponding modeled Vs profile are presented in Figure 7. The resolution decreases gradually with depth, because of loss of sensitivity of the dispersion curve to changes in Vs at greater depth. The Vs and Vp profile used to match the field data are provided in tabular form as Tables 1-5. The modeled shear-wave velocity profiles for MASW arrays A, B, and C (Tables 1-3) are all in relative agreement with one another. Soils in the upper 1.75 — 3 ft have a very low S-wave velocity of 300-350 ft/s (corresponding to an approximate 600 — 700 ft/s P-wave velocity). There is a clear S-wave velocity contrast for arrays B and C at a depth of approximately 10 ft. 6243 Versar 8 July 6, 2006