GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 210-6
Presentation Time: 2:45 PM


BORELLA, Josh W., Frontiers Abroad, University of Canterbury, Private Bag 4800, Christchurch, 8041, New Zealand and QUIGLEY, Mark, School of Earth Sciences, University of Melbourne, Melbourne, VIC 3010, Australia

Paleoseismic studies commonly use sedimentary geological features to estimate the spatial and temporal characteristics of future hazard. In this talk we first compare the locations, physical characteristics, and lithologies of rockfall boulders deposited during the 2010-2011 Canterbury earthquake sequence (n=185) in New Zealand with those deposited prior to the CES (n=1093). CES (Anthropocene) boulders traveled approximately 100 to 350 m further downslope than their analogous (syn- to pre-middle Holocene) pre-CES counterparts because intervening anthropogenic deforestation reduced hillslope resistance to CES rockfall transport. Exceptions to this include areas where remobilization of pre-CES boulders has occurred by post-depositional processes such as debris flows, and where collisional impacts of CES with pre-CES boulders reduced CES boulder runouts. We expand our study to investigate the roles of anthropogenic activity on the characteristics of liquefaction features at the surface and in the subsurface sedimentary record in Christchurch through the CES. Liquefaction sand blows and feeder dikes reflect complex interactions between natural and anthropogenic sediments and engineered structures such drains and irrigation systems. A considered earth-systems approach is required when using preserved distributions of pre-Anthropocene rockfall and liquefaction deposits to predict the severity and extent of future events.