Mapping Fundamental-Mode Site Periods and Amplifications from Thick Sediments: An Example from the Jackson Purchase Region of Western Kentucky, Central United States

ABSTRACT V S 30 is currently used as a key proxy to parameterize site response in engineering design and other applications. However, it has been found that VS30 is not an appropriate proxy, because it does not reliably correlate with site response. Therefore, the VS30-based National Earthquake Hazards Reduction Program site maps may not capture regional site responses. In earthquake engineering, site resonance, which can be characterized by the fundamental mode with a site period (Tf) and its associated peak amplification (A0), is the primary site-response concern. Mapping Tf and A0 is thus essential for accurate regional seismic hazard assessment. We developed a 3D shear-wave velocity model for the Jackson Purchase Region of western Kentucky, based on shear-wave velocity profiles interpreted from seismic reflections and refractions, mapped geologic units, and digital-elevation-model datasets. We generated shear-wave velocity profiles at grid points with 500 m spacing from the 3D model and performed 1D linear site-response analyses to obtain Tf and A0, which we then used to construct contour maps for the study area. Our results show that Tf and A0 maps correlate with the characteristics of regional geology in terms of sediment thicknesses and their average shear-wave velocities. We also observed a strong dependency of A0 on bedrock shear-wave velocities. The mapped Tf and A0 are consistent with those estimated from borehole transfer functions and horizontal-to-vertical spectral ratio analyses at broadband and strong-motion stations in the study area. Our analyses also demonstrate that the depth to bedrock (Zb) is correlated to Tf, and the average sediment shear-wave velocity (VS-avg) is correlated to A0. This implies that Zb and VS-avg may be considered as paired proxies to parameterize site resonance in the linear-elastic regime.

Up from the farm: a global microhistory of rural Americans and Africans in the First World War

Were the effects of First World War truly similar globally? A comparison of how the conflict was perceived by two extremely different groups of rural people – southern Americans of the Jackson Purchase region of far western Kentucky and Africans in the small British Protectorate of Nyasaland in south central Africa – makes their microhistories significant rather than trivial by placing them a global context. In the early twentieth century, both groups were not only rural, but removed, decidedly disconnected from each other. Yet, drawing on documentary evidence, especially interviews with the last generation of First World War survivors in both regions, offers a significant perspective on how similar their experiences actually became in the crucible of a global war. The call to arms, their recruitment and resistance to service, combat adversities and cultural experiences, post-war disillusionments and triumphs, and especially the economic consequences of their war provide penetrating insights into the wide-ranging ordeals and opportunities that this first truly global event offered peoples worldwide.

Where Five Rivers Meet

The convergence of five river systems in far western Kentucky significantly influenced the progress of human settlement and activity over the past several thousand years in the area now known as the Jackson Purchase. The geological history of the Jackson Purchase set the stage for the development of unique land- and waterscapes with natural histories very different from the rest of Kentucky. The Ohio, the Mississippi, the Cumberland, and the Tennessee Rivers define the present boundaries of the Purchase area, and the smaller Clarks River provides the major drainage through its midsection. Major geological, hydrological, and human historical events including the New Madrid earthquakes, Civil War, floods, water-borne diseases, the ever-changing focus of agriculture and industry, and 20th century dam building, including construction of two major hydroelectric reservoirs (Kentucky Lake and Lake Barkley) all affected peoples’ choices of where to live and how to use the land and water resources of the region.Today, western Kentuckians are actively engaged in preserving the quality of the region’s water resources because of the recreational, agricultural, industrial, transportation, and ecological services they provide.