Liquefaction Induced during the 2010–2011 Canterbury, New Zealand, Earthquake Sequence and Lessons Learned for the Study of Paleoliquefaction Features

Abstract

ABSTRACT Very large to moderate earthquakes in the 2010–2011 Canterbury sequence induced liquefaction in parts of Christchurch city and the surrounding region on the South Island of New Zealand. Detailed information gathered about this case of recurrent liquefaction offers important lessons for the study of paleoliquefaction features and the paleoearthquakes that caused them. The Canterbury case demonstrates that liquefaction features are important indicators of strong ground shaking in regions where fault ruptures do not necessarily propagate to the surface, may be masked by later sedimentation, or are otherwise difficult to recognize. Comparison of the liquefaction fields produced by the 2010 M 7.1 Darfield and 2011 M 6.2 Christchurch earthquakes in the Canterbury sequence highlights the influence of site conditions on the geographical distribution of liquefaction features and underscores the need to consider liquefaction susceptibility of sediment and depth of the water table when using paleoliquefaction features to interpret the source area and magnitude of paleoearthquakes. The epicentral distance and size of liquefaction features that formed during the Darfield and Christchurch earthquakes corroborate and further constrain empirical relations used to estimate source areas and magnitudes of paleoearthquakes. Formation of compound sand blows, composed of multiple sand–silt couplets resulting from repeated liquefaction during the Canterbury earthquakes, supports previous interpretations of compound sand blows in the central and western United States. In addition, paleoliquefaction features found in excavations of sand blows that formed during the 2010–2011 Canterbury earthquakes indicate that sites of modern liquefaction are prime targets for paleoliquefaction studies. The depositional environments where liquefaction features form and are preserved help to guide searches for paleoliquefaction features. Information from many sites across a region is needed to develop a chronology of past liquefaction events, to define their liquefaction fields, and to estimate the source areas and magnitudes of paleoearthquakes.