INVESTIGATION OF MACROSEISMIC DATA, MICROEARTHQUAKES, AND PALEOLIQUEFACTION ASSOCIATED WITH THE 1867 WAMEGO EARTHQUAKE IN EASTERN KANSAS

Historical felt earthquakes and instrumentally recorded microseismicity in eastern Kansas and Missouri have been attributed to the movement of the Nemaha Ridge and Humboldt fault (NRHF). Our investigations of the NRHF have concentrated on relocation of microearthquakes in the Kansas catalog, reevaluation of the 1867 earthquake felt reports, and field studies to determine the presence or absence of sedimentary evidence of earthquake-induced liquefaction. Microearthquakes in the Kansas catalog have been relocated in a joint inversion for 3D seismic velocity and hypocenter constrained by recent results from crustal imaging. This improved set of hypocenters reaffirms the loose association of seismicity with the basement NRHF structure, even though seismicity does not seem to follow a single, well-defined fault feature. Overall, the association of microearthquakes with the NRHF suggests that it remains a potential source of large earthquakes. Our field investigations confirm that sedimentary deposits with moderate liquefaction susceptibility are present in the vicinity of Wamego and Wabaunsee, Kansas. Soft sediment deformation features, including flame structures, dish structures, and psuedonodules, are present in the late Holocene floodplain deposits of the Kansas River. These features may have formed by liquefaction or by processes unrelated to seismic activity, such as sediment dewatering. We found no clastic dikes that can be unequivocally attributed to seismically-induced liquefaction. Our initial results suggest that liquefaction features are not pervasive in this region. However, additional field investigations are still necessary to complete the assessment of liquefaction features.