![]() Differential LiDAR applications in earthquake studies have been used to map deformation along fault zones (e.g., Duffy et al., 2013 Oskin et al., 2012) however, this is the first differential LiDAR study showing the cumulative surface effects of earthquake shaking and faulting on an urban environment. In this paper, we summarize differential vertical and horizontal ground movements in Christchurch, New Zealand, using airborne LiDAR survey data captured prior to, during, and after the 2010 to 2011 Canterbury Earthquake Sequence (CES). However, the influence of moderate magnitude (i.e., MW 6–7) earthquakes, which can occur in both interplate and intraplate settings, on coastal flood and sea-level hazards is not well characterized and not typically included in studies that assess the future vulnerability of coastal populations (McGranahan et al., 2007). The 1964 MW 9.0 Alaska earthquake caused tidal marshes and wetlands to subside up to 2 m (Shennan and Hamilton, 2006) the 2005 MW 8.7 Nias earthquake caused up to 3 m in coastal uplift proximal to the trench and 1 m of more distal coastal subsidence (Briggs et al., 2006) and the 2011 MW 9.0 Tohoku earthquake caused subsidence up to 1.2 m along the Pacific Coast of northeastern Japan (Geospatial Information Authority of Japan, 2011, cited in IPCC, 2014). ![]() Great (MW ≥ 8.5) earthquakes on subduction zones may cause abrupt and dramatic elevation changes to coastal environments. Geospatial data, such as satellite-based synthetic aperture radar and airborne light detection and ranging (LiDAR), are increasingly being used to measure surface subsidence and delineate areas prone to flood and sea-level rise hazards (Dixon et al., 2006 Wang et al., 2012 Webster et al., 2006), thereby assisting land-use planning and management decisions (Brock and Purkis, 2009). Coastal population growth and concentration, economic development, and urbanization are expected to greatly increase exposure and loss to the impacts of rela-tive sea-level rise (Nicholls and Cazenave, 2010 IPCC, 2014) and coastal flooding (Hanson et al., 2011 Hallegatte et al., 2013) through the next century, defining one of society’s greatest challenges. Cities constructed on low-lying coastal and river plains are highly vulnerable to ocean-sourced hazards (e.g., sea-level rise, storm surges, tsunamis) and terrestrial hazards (e.g., surface subsidence and compaction, flooding, erosion, sedi-ment supply changes, groundwater table changes) induced by natural and/or anthropogenic processes (Syvitski et al., 2009 Nicholls and Cazenave, 2010). IntroductionĪpproximately 10% of the world’s population inhabits low-lying (≤10 m above sea level) coastal areas, and most of this popu-lation is contained within densely populated urban centers (McGranahan et al., 2007). Manuscript received accepted 31 July 2014. *Emails: Hughes: Quigley: Ballegooy: Deam: Bradley: Hart: Measures. Our findings highlight the potential for moderate magnitude (MW 6–7) earthquakes to cause major topo-graphic changes that influence flood hazard in coastal settings. Flood mitigation along the large regional Waimakariri River north of Christchurch may have, paradoxically, increased the long-term flood hazard in the city by halting long-term aggradation of the alluvial plain upon which Christchurch is situated. Differential tectonic movement and associated narrowing of downstream river chan-nels decreased channel gradients and volumetric capacities and increased upstream flood hazards. ![]() ![]() Additional shaking effects included river channel narrowing and shallowing, due primarily to liquefaction, and lateral spreading and sedimen-tation, which further increased flood hazard. ![]() Shaking caused floodplain subsidence in excess of 0.5 to 1 m along tidal stretches of the two main urban rivers, greatly enhancing the spatial extent and severity of inundation hazards posed by 100-year floods, storm surges, and sea-level rise. Differencing of pre- and post-earthquake LiDAR data reveals land surface and waterway deformation due to seismic shaking and tectonic displacements above blind faults. Airborne light detection and ranging (LiDAR) data were acquired over the coastal city of Christchurch, New Zealand, prior to and throughout the 2010 to 2011 Canterbury Earthquake Sequence. ![]()
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