M. Tuttle & Associates

Abstract This study presents a micromorphological analysis of liquefaction features (dykes, sills and sand blows) associated with the 2010 to 2011 Canterbury Earthquakes Sequence, dykes of an earlier generation of liquefaction (palaeoliquefaction) and hosting soil. The aim of this research was to determine whether diagnostic features existed that would allow robust identification of liquefaction features and discrimination of different generations of liquefaction features in thin sections. This study serves to enhance the tools available to support palaeoliquefaction studies and earthquake hazard assessment. Similarities were found in the sedimentary fabric between all forms and ages of liquefaction features distinct from hosting soil. Palaeoliquefaction features could also be distinguished on the basis of microscopic pedogenic characteristics. Liquefaction and palaeoliquefaction were investigated in two distinctive sedimentary settings: the floodplain of the Halswell River, and coastal sand dunes near or in Christchurch. Analysis was carried out on thin sections prepared from resin‐impregnated blocks of soil sediment hosting the liquefaction features. The fabric of modern liquefaction features in the alluvial and coastal system is similar, both showing a single grain micro‐structure, with moderate to well‐sorted grains with many simple packing voids and planar voids. In both environments it was possible to see evidence of fluidization such as water escape structures, cutans and silt caps. The palaeoliquefaction fabric can be distinguished from the modern liquefaction fabric by the presence of textural pedogenic features in the form of silt coating of grains, infilling of planar voids, coating and hypocoating of voids and excrement pedofeatures. The results presented in this manuscript demonstrated how thin section analysis can be a valuable tool to corroborate field identification of liquefaction features, and to discriminate between features of different relative ages where stratigraphic evidence is equivocal.

Liquefaction features and the geologic environment in which they formed were carefully studied at two sites near Lincoln in southwest Christchurch. We undertook geomorphic mapping, excavated trenches, and obtained hand cores in areas with surficial evidence for liquefaction and areas where no surficial evidence for liquefaction was present at two sites (Hardwick and Marchand). The liquefaction features identified include (1) sand blows (singular and aligned along linear fissures), (2) blisters or injections of subhorizontal dikes into the topsoil, (3) dikes related to the blows and blisters, and (4) a collapse structure. The spatial distribution of these surface liquefaction features correlates strongly with the ridges of scroll bars in meander settings. In addition, we discovered paleoliquefaction features, including several dikes and a sand blow, in excavations at the sites of modern liquefaction. The paleoliquefaction event at the Hardwick site is dated at A.D. 908–1336 , and the one at the Marchand site is dated at A.D. 1017–1840 (95% confidence intervals of probability density functions obtained by Bayesian analysis). If both events are the same, given proximity of the sites, the time of the event is A.D. 1019–1337. If they are not, the one at the Marchand site could have been much younger. Taking into account a preliminary liquefaction‐triggering threshold of equivalent peak ground acceleration for an M w 7.5 event (PGA7.5) of 0.07 g , existing magnitude‐bounded relations for paleoliquefaction, and the timing of the paleoearthquakes and the potential PGA7.5 estimated for regional faults, we propose that the Porters Pass fault, Alpine fault, or the subduction zone faults are the most likely sources that could have triggered liquefaction at the study sites. There are other nearby regional faults that may have been the source, but there is no paleoseismic data with which to make the temporal link. Online Material: Figures showing areas of liquefaction, trench logs, information on dike and sand‐blow parameters, dike azimuths, core logs, radiocarbon samples, and OxCal analysis, and tables detailing units exposed in the trenches and stereonets.

The Indian Ocean tsunami of 26 December 2004 shows poignantly that catastrophic tsunamis are too infrequent for their hazard to be characterized by historical records alone. Long‐term geologic records provide opportunities to assess tsunami hazards more fully. Telltale deposits left by tsunamis help assess water depth and velocity of past inundations, estimate source locations, and aid in understanding how tsunamis affect the ecology and geomorphology of coastlines. Dated deposits allow estimates of times and recurrence intervals of past tsunamis. Such information guides mitigation efforts and may reduce losses from future tsunamis.

VORTIGERN CRANCOCC, ESQ Get access JOSEPH LOVERTI JOSEPH LOVERTI 1763 Tuttle Avenue, Dayton, Ohio 45403, U.S.A. Search for other works by this author on: Oxford Academic Google Scholar Notes and Queries, Volume 21, Issue 11, November 1974, Pages 421-b–421, https://doi.org/10.1093/nq/21-11-421b Published: 01 November 1974