To evaluate the geospatial hazard relationships between recent(contemporary) rockfalls and their prehistoric predecessors, we compare thelocations, physical characteristics, and lithologies of rockfall bouldersdeposited during the 2010–2011?Canterbury earthquake sequence?(CES)(n=185) with those deposited prior to the CES (n=1093). Populationratios of pre-CES to CES boulders at two study sites vary spatially from?～5:1 to?8.5:1. This is interpreted to reflect (i)?variations inCES rockfall flux due to intra- and inter-event spatial differences inground motions (e.g.,?directionality) and associated variations in sourcecliff responses; (ii)?possible variations in the triggering mechanism(s),frequency, flux, record duration, boulder size distributions, andpost-depositional mobilization of pre-CES rockfalls relative to CESrockfalls; and (iii)?geological variations in the source cliffs of CES andpre-CES rockfalls. On interfluves, CES boulders traveled approximately 100?to 250m further downslope than prehistoric (pre-CES) boulders. This is interpreted to reflect reduced resistance to CES rockfall transport due to preceding anthropogenic hillslope de-vegetation. Volcanic breccia boulders are more dimensionally equant and rounded, are larger, and traveled further downslope than coherent lava boulders, illustrating clear geological control on rockfall hazard. In valley bottoms, the furthest-traveled pre-CES boulders are situated further downslope than CES boulders due to (i)?remobilization of pre-CES boulders by post-depositional processes such as debris flows and (ii)?reduction of CES boulder velocities and travel distances by collisional impacts with pre-CES boulders. A considered earth-systems approach is required when using preserved distributions of rockfall deposits to predict the severity and extents of future rockfall events.
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