Coseismic river avulsion on surface rupturing faults: Assessing earthquake-induced flood hazard

Surface-rupturing earthquakes can produce fault displacements that abruptly alter the established course of rivers. Several notable examples of fault rupture-induced river avulsions (FIRAs) have been documented, yet the factors influencing these phenomena have not been examined in detail. Here, we use a recent case study from New Zealand's 2016 Kaikoura earthquake to model the coseismic avulsion of a major braided river sub-jected to-7-m vertical and-4-m horizontal offset. We demonstrate that the salient characteristics of the avul-sion can be reproduced with high accuracy by running a simple two-dimensional hydrodynamic model on synthetic (pre-earthquake) and real (post-earthquake) deformed lidar datasets. With adequate hydraulic inputs, deterministic and probabilistic hazard models can be precompiled for fault-river intersections to improve multihazard planning. Flood hazard models that ignore present and potential future fault deformation may underestimate the extent, frequency, and severity of inundation following large earthquakes.

Automated summary

Surface-rupturing earthquakes can cause sudden changes in rivers by displacing faults. Although there have been several documented cases of fault rupture-induced river avulsions (FIRAs), the factors influencing these phenomena have not been thoroughly studied. In this study, a case study from the 2016 Kaikoura earthquake in New Zealand was used to model the coseismic avulsion of a major braided river that experienced a -7m vertical and -4m horizontal offset. The results show that a simple two-dimensional hydrodynamic model can accurately reproduce the avulsion characteristics. This research highlights the importance of considering fault deformation in flood hazard models to properly assess the extent and severity of inundation following large earthquakes.