At 5,150 feet above sea level on the Laramie Plains, Casper deals with a mix of wind-blown silt and weathered sandstone that amplifies ground motion differently from one parcel to the next. The 1984 M5.3 earthquake near Douglas rattled downtown Casper hard enough to crack unreinforced masonry, and since then the city has tightened building requirements in critical areas. A seismic microzonation study maps these variations block by block, giving engineers the site-specific spectra and amplification factors that generic code values simply cannot capture. We run MASW transects across the North Platte River terraces to get Vs30 profiles, then overlay the results with liquefaction susceptibility screening in the alluvial deposits near the river.
Two lots separated by 200 feet in Casper can face a 40 percent difference in short-period spectral acceleration. We map that difference.
