The Stratigraphy of Compound Sand Blows at Sites of Recurrent Liquefaction: Implications for Paleoseismicity Studies

Abstract

Paleoliquefaction studies provide valuable information for seismic hazard analyses in areas where the return period of moderate to large events is longer than the duration of the historical earthquake catalog (e.g., Central-Eastern and Pacific Northwest United States). Toward this end, paleoliquefaction studies require accurate and detailed assessments of individual features and of the extent of the paleoliquefaction field for the event, with the difficulty of accurately interpreting field observations increasing in areas where recurrent liquefaction was triggered by spatiotemporally clustered paleo events. Accordingly, undisturbed features formed by recurrent liquefaction during the 2010–2011 Canterbury, New Zealand, earthquake sequence were studied to facilitate interpretation of paleoliquefaction analogs. Silt drapes demarcated multiple episodes of liquefaction in the sand blows, with the thickness of the silt drapes correlating to the fines content of the liquefied source stratum. However, no ubiquitous trends in the spatial sorting of grain sizes in the coarser fraction of the ejecta underlying silt drapes were observed. This study provides a modern analog to recurrent paleoliquefaction evidence and has important implications for interpretation of seismic hazards.