An acoustic inversion for bottom geoacoustic properties from an unexpected explosion in the South China Sea (SCS) is presented. Horizontal beamforming is performed to find the source azimuthal direction and the water wave part of the modal dispersion curve is used to find the source range. The localization result shows that the detonation occurred in the direction of east-north east and about 40 km distant from the receiver. To perform the bottom inverse, we use a broadband linear inverse technique employing the modal group velocity, which is inferred from the modal arrival time and source range. In the end, a four-layered bottom model is created, which is consistent with both our explosion data and independent source tow data. The resolution and variance of the estimate are also presented. In conclusion, this bottom model should be widely applicable for modeling broadband sound propagation in the ASIAEX SCS experiment site.