The role of local soil-induced amplification in the 27 July 1980 northeastern Kentucky earthquake

Amplification of earthquake ground motions by near-surface soil deposits was believed to have occurred in Maysville, Kentucky, U.S.A. during the northeast Kentucky (Sharpsburg) earthquake (m_b,Lg 5.3) of July 27, 1980. The city of Maysville, founded on approximately 30 m of Late Quaternary Ohio River flood plain alluvium, was 52 km from the epicenter, but experienced equivalent or higher Modified Mercalli Intensity (MMI) VII, compared with the epicentral area of the earthquake (i.e., MMI VI-VII). In this study, dynamic soil properties were obtained at 10 sites in Maysville using seismic P-wave and S-wave (SH-mode) refraction and reflection methods. Synthetically generated composite time histories and limited geotechnical information, along with the measured dynamic properties, were used to perform one-dimensional linear-equivalent amplification analyses. The results indicated the soils generated ground-motion amplification factors between 3.0 and 6.0 and at a frequency range between 2.0 and 5.0 Hz (0.2 to 0.5 s). The building damage in Maysville from the Sharpsburg earthquake was predominantly found in one- to three-story masonry structures. The estimated fundamental period for one- to three-story masonry buildings is approximately 0.11 to 0.26 s (3.8 to 9 Hz). These correlations suggest the elevated ground motion intensity in Maysville can be accounted for by near-surface soil-amplification effects and resonance of the ground motion by the buildings (i.e., double resonance).