D. K. Keefer R.W. Jibson 1993 <p>By analyzing two landslides in the New Madrid seismic zone, we develop an approach for judging if a landslide or group of landslides of unknown origin was more likely to have formed as a result of earthquake shaking or in aseismic conditions. The two landslides analyzed are representative of two groups of land-slides that previous research on the geomorphology and regional distribution of landslides in this region indicates may have been triggered by the 1811-1812 New Madrid earthquakes. Slope-stability models of aseismic conditions show that neither landslide is likely to have formed aseismically even in unrealistically high ground-water conditions. Dynamic stability analysis using Newmark's method shows that both slides probably would have experienced large inertial displacements during earthquake shaking similar to that which occurred in 1811-1812; these displacements are large enough that catastrophic failure is highly probable. Thus, the stability analyses are consistent with other lines of evidence that these landslides formed as a result of strong earthquake shaking during the 1811-1812 earthquakes.</p><p>Our analysis yields a general relationship between Newmark landslide displacement, earthquake shaking intensity, and the critical acceleration of a landslide. Using this relationship, we estimate the minimum shaking intensities required to trigger the types of landslides studied: an<span>&nbsp;</span><i>m_b</i><span>&nbsp;</span>= 5.8 or M = 5.9 earthquake is the lower bound threshold at zero epicentral distance that could trigger catastrophic movement of typical block slides in the New Madrid seismic zone; for earth flows,<span>&nbsp;</span><i>m_b</i><span>&nbsp;</span>= 5.4 or M = 5.3 is the threshold earthquake.</p> application/pdf 10.1130/0016-7606(1993)105<0521:AOTSOO>2.3.CO;2 en Geological Society of America Analysis of the seismic origin of landslides: Examples from the New Madrid seismic zone article