During preliminary design, a six-story medical office building near Poplar Avenue received an urgent signal. The geotechnical investigation highlighted deep alluvial clays, but the critical concern was not bearing capacity—it would be the site's shaking behavior. Memphis lies within the New Madrid Seismic Zone, where the deep, soft sediments of the Mississippi Embayment can significantly amplify ground motion. To assess this, we conducted a seismic microzonation study that integrated surface wave testing with deep borings to determine site period and spectral acceleration. The outcome: a site-specific response spectrum that lowered design ground motions by 18% relative to the default ASCE 7 code spectrum, allowing the structural team to avoid overdesigning the lateral system. In a city where a recurrence of the 1811-1812 earthquakes is a question of when, not if, accounting for local site effects is not optional—it determines whether a building withstands the shaking.
In the Mississippi Embayment, two sites a half-mile apart can experience a 40% difference in spectral acceleration. Microzonation quantifies that before you break ground.
