Investigation of microearthquakes, macroseismic data, and liquefaction associated with the 1867 Wamego earthquake in eastern Kansas

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Bulletin of the Seismological Society of America
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Historical felt earthquakes and instrumentally recorded microseismicity in eastern Kansas and western Missouri have been attributed to the movement of the Nemaha Ridge and Humboldt fault zone (NRHF). Our investigations of the NRHF have concentrated on relocation of microearthquakes in the Kansas catalog, re-evaluation 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 with 3D seismic velocity variations. This improved set of hypocenters affirms 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 and dish structures. 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 several clastic dikes that may be attributed to seismically induced liquefaction. Our initial results suggest that liquefaction features are present but may not be pervasive in this region. These data imply that the 5.2 magnitude of the 1867 Wamego earthquake may characterize the seismic source in this location. However. additional field investigations are still necessary to complete the assessment for liquefaction features.


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