Effect of soil aging on assessing magnitudes and accelerations of prehistoric earthquakes

Increase in strength due to aging of sands is reflected in higher blow counts and tip resistance values in penetration resistance measurements. This affects the magnitudes and peak ground acceleration estimates of prehistoric earthquakes obtained from an analysis of geotechnical observations at paleoliquefaction sites in the South Carolina Coastal Plain. In this study, corrections were made to account for the effects of soil aging, which were neglected in earlier estimates. The results show that when the effects of aging of soils on their geotechnical properties are incorporated, the resulting back-calculations reduced earlier magnitude estimates of prehistoric earthquakes by about 0.9 units. The peak ground acceleration estimates were reduced by about 15% for those earthquakes originally estimated at approximately 0.15 g. For those earthquakes whose original estimates were greater than 0.2 g, there was no noticeable change when a correction was made for the aging of soils.