Microzonation and liquefaction susceptibility analyses from borehole data

     Within the frame work of this study, 1094 borehole data (Figure 1) were evaluated individually and site profiles with respect to soil types and shear wave velocities were established. Shear wave velocities are calibrated to match the values determined from the ambient noise records. Site response a nalysis were conducted using PGA scaled 12 records for the 1094 soil profiles for two earthquake hazard levels corresponding to 2475 and 475 year return periods. A total of 25256 site response analyses were performed and earthquake properties on the ground surface were estimated with respect to peak ground and spectral accelerations, peak ground velocity and site amplification.

     Microzonation with respect to ground shaking intensity was based on two parameters: (1) average spectral accelerations calculated between the 0.1 and 1 sec periods using the average acceleration spectrum calculated for each boring from the results of the twelve site response analysis conducted for each location, (2) the peak spectral accelerations calculated using equivalent shear wave velocities. The zonation with respect to ground shaking intensity (Figure 2) is produced as the superposition of these two parameters with respect to three regions where zone AGS shows the areas with very low ground shaking intensity, zone BGS shows the areas with low to medium ground shaking intensity, and zone CGS shows the areas with high round shaking intensity.

     The liquefaction susceptibility was determined for each cell based on the latest state-of-the art methods available in the literature. The safety factors were determined for each representative borehole containing liquefiable sand or silt layers. The susceptibility map (Figure 3) is produced with respect to three regions where zone AL shows the areas with very low liquefaction susceptibility, zone BL shows the areas with low to medium liquefaction susceptibility, and zone CL shows the areas with high liquefaction susceptibility. The liquefaction susceptibility map produced indicates that in major part of Dubai, liquefaction susceptibly is very low and thus negligible.