Review Article: Potential geomorphic consequences of a future great (<i>M</i><sub>w</sub> = 8.0+) Alpine Fault earthquake, South Island, New Zealand

Abstract

Abstract. The Alpine Fault in New Zealand's South Island has not sustained a large magnitude earthquake since ca. AD 1717. The time since this rupture is close to the average inferred recurrence interval of the fault (∼ 300 yr). The Alpine Fault is therefore expected to generate a large magnitude earthquake in the near future. Previous ruptures of this fault are inferred to have generated M w = 8.0 or greater earthquakes and to have resulted in, amongst other geomorphic hazards, large-scale landslides and landslide dams throughout the Southern Alps. There is currently 85 % probability that the Alpine Fault will cause a M w = 8.0+ earthquake within the next 100 yr. While the seismic hazard is fairly well understood, that of the consequential geomorphic activity is less well studied, and these consequences are explored herein. They are expected to include landsliding, landslide damming, dam-break flooding, debris flows, river aggradation, liquefaction, and landslidegenerated lake/fiord tsunami. Using evidence from previous events within New Zealand as well as analogous international examples, we develop first-order estimates of the likely magnitude and possible locations of the geomorphic effects associated with earthquakes. Landsliding is expected to affect an area > 30 000 km 2 and involve > 1 billion m 3 of material. Some tens of landslide dams are expected to occur in narrow, steep-sided gorges in the affected region. Debris flows will be generated in the first long-duration rainfall after the earthquake and will continue to occur for several years as rainfall (re)mobilises landslide material. In total more than 1000 debris flows are likely to be generated at some time after the earthquake. Aggradation of up to 3 m will cover an area > 125 km 2 and is likely to occur on many West Coast alluvial fans and floodplains. The impact of these effects will be felt across the entire South Island and is likely to continue for several decades.

A precipiton‐based approach to model hydro‐sedimentary hazards induced by large sediment supplies in alluvial fans

“…Alluvial fans located at the front of active mountain ranges can be submitted to large sediment deliveries during short time scales. The extreme geomorphic conditions experienced in these areas such as intense precipitations, earthquakes and steep slopes can trigger frequent mass wasting processes that supply large volumes of sediments in the fluvial network (Dadson et al ., ; Yanites et al ., ; Robinson and Davies, ). The progressive evacuation of landslide‐derived sediments from their location in the upstream catchment to the alluvial fan can alter river dynamics, for instance, by depositing a high quantity of sediment along its path.…”

Rapid post-earthquake modelling of coseismic landslide intensity and distribution for emergency response decision support

“…Landslides are also a key inhibitor of relief and reconstruction via the blocking of critical infrastructure and present a chronic hazard, with post-earthquake landslide rates remaining elevated compared to pre-earthquake rates for at least several years (Marc et al, 2015). Rapidly identifying the distribution of landslides following an earthquake is therefore crucial for understanding the total earthquake impacts (Robinson and Davies, 2013); aiding immediate emergency response efforts, including search and rescue; and assessing the longer-term post-earthquake risks. If an assessment of landsliding is to be useful for emergency response, it needs to be rapid, i.e.…”

Landslides control the spatial and temporal variation of channel width in southern Taiwan: Implications for landscape evolution and cascading hazards in steep, tectonically active landscapes

“…While the landslides themselves can be quite catastrophic (Tsou et al, 2011), the propagating impacts of the landslide material through the landscape can cause significant, long-lived hazards (Nguyen et al, 2013). For example, aggradation in downstream riverbeds following the event can change flood inundation patterns and frequency (Stover and Montgomery, 2001;Chen and Petley, 2005;Lane et al, 2007;Robinson and Davies, 2013;Croissant et al, 2017a) as well as influence channel bank mobility (Lisle, 1982;Lane et al, 2007). Regions with mountainous topography and high populations, such as Taiwan, are particularly vulnerable to cascading hazards associated with regional landsliding initiated by earthquakes and extreme precipitation.…”