This photograph shows an area where sand vented extensively to the surface within the region of most severe shaking during the 1811-12 New Madrid earthquakes. The vented sand forms a sheet everywhere more than a meter thick in the area shown. Tens of kilometers in the vicinity are veneered with this thickness. Whereas the venting in the photo has been spectacular, the severity of the liquefaction here makes it poor for back-calculating the strength of shaking of the 1811-12 earthquakes. This report points out how to select regions that are suitable for this purpose and presents a new methodology for doing the quantitative analysis. (From U.S. Geological Survey Open-File Report OF98-488 - http://pubs.usgs.gov/of/of98-488/).
|A new methodology is proposed for the geotechnical analysis of strength of paleoseismic shaking using liquefaction effects. The proposed method provides recommendations for selection of both individual and regionally located test sites, techniques for validation of field data for use in back-analysis, and use of a recently developed energy-based solution to back-calculate paleoearthquake magnitude and strength of shaking. The proposed method allows investigators to qualitatively assess the influence of post-earthquake density change and aging. The proposed method also describes how the back-calculations from individual sites should be integrated into a regional assessment of paleoseismic parameters.|