IMPLICATIONS OF OBSERVED LIQUEFACTION DURING THE 2011 CENTRAL VIRGINIA EARTHQUAKE ON REGIONAL PALEOLIQUEFACTION STUDIES

Liquefaction is a phenomenon that occurs when the soil skeleton of loose, saturated sandy soil collapses and there is a temporary transfer of the overburden stress from the soil skeleton to the pore fluid. The collapse of the soil skeleton can be initiated in a variety of ways, one of which is earthquake shaking. The occurrence of liquefaction often manifests itself on the ground surface in the form of sand boils. The occurrence of liquefaction has been documented in every major earthquake, with the smallest magnitude event known to have triggered liquefaction being the M~4.2, 1898 Val di Noto, Italy earthquake. Following the 2011, M5.8 Central Virginia earthquake the authors, along with others, searched the epicentral region for evidence of liquefaction. In total, three suspected liquefaction sites were found: one definite liquefaction site, one probable liquefaction site, and one questionable liquefaction site. Soil samples were collected and Dynamic Cone Penetration (DCP) Tests were performed at the sites of definite and probable liquefaction. The grain size distributions of the liquefied soils were in general accord with the range for “Potentially Liquefiable Soils” proposed by Tsuchida (1970). Using the DCP Test results, the predicted factors of safety against liquefaction at the two sites were close to 1.0, which is in accord with the observed small liquefaction features. Based on this information, the paucity of observed liquefaction during the 2011 Central Virginia earthquake is most likely due to the relatively low liquefaction susceptibility of soils in the region. This conclusion gives credence to the use of regional magnitude bound curves for estimating the magnitudes of paleoearthquakes, with the observations from the 2011 Central Virginia earthquake being in line with the Central-Eastern US magnitude bound curve proposed by Olson, Green, and Obermeier (2005).