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Earthquake-Induced Chains of Geologic Hazards: Patterns

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Earthquake-Induced Chains of Geologic Hazards: Patterns REVIEW ARTICLE Earthquake‐Induced Chains of Geologic Hazards: 10.1029/2018RG000626 Patterns, Mechanisms, and Impacts Key Points: Xuanmei Fan1 , Gianvito Scaringi1,2 , Oliver Korup3, A. Joshua West4 , • Coupled surface processes initiated 5 5 3 6 by strong seismic shaking are Cees J. van Westen , Hakan Tanyas , Niels Hovius , Tristram C. Hales , important hazards in mountain Randall W. Jibson7 , Kate E. Allstadt7 , Limin Zhang8, Stephen G. Evans9, Chong Xu10, landscapes Gen Li4 , Xiangjun Pei1, Qiang Xu1, and Runqiu Huang1 • Earthquake‐induced landslides pose challenges to hazard and risk 1State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu University of Technology, assessment, management, and 2 mitigation Chengdu, China, Institute of Hydrogeology, Engineering Geology and Applied Geophysics, Faculty of Science, Charles • Multidisciplinary approaches University, Prague, Czech Republic, 3Institute of Earth and Environmental Science, University of Potsdam, Potsdam, further the understanding of the Germany, 4Department of Earth Sciences, University of Southern California, Los Angeles, CA, USA, 5Faculty of Geo‐ earthquake hazard cascade, yet Information Science and Earth Observation (ITC), University of Twente, Enschede, Netherlands, 6School of Earth and challenges remain Ocean Sciences, Cardiff University, Cardiff, UK, 7U.S. Geological Survey, Golden, CO, USA, 8Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Hong Kong, 9Department of Earth Supporting Information: 10 • Supporting Information S1 and Environmental Sciences, University of Waterloo, Waterloo, Ontario, Canada, Key Laboratory of Active Tectonics and Volcano, Institute of Geology, China Earthquake Administration, Beijing, China Correspondence to: Q. Xu and R. Huang, Abstract Large earthquakes initiate chains of surface processes that last much longer than the brief [email protected]; moments of strong shaking. Most moderate‐ and large‐magnitude earthquakes trigger landslides, ranging [email protected] from small failures in the soil cover to massive, devastating rock avalanches. Some landslides dam rivers and impound lakes, which can collapse days to centuries later, and flood mountain valleys for hundreds of Citation: kilometers downstream. Landslide deposits on slopes can remobilize during heavy rainfall and evolve into Fan, X., Scaringi, G., Korup, O., West, debris flows. Cracks and fractures can form and widen on mountain crests and flanks, promoting increased A. J., van Westen, C. J., Tanyas, H., et al. fl (2019). Earthquake‐induced chains of frequency of landslides that lasts for decades. More gradual impacts involve the ushing of excess debris geologic hazards: Patterns, downstream by rivers, which can generate bank erosion and floodplain accretion as well as channel mechanisms, and impacts. Reviews of avulsions that affect flooding frequency, settlements, ecosystems, and infrastructure. Ultimately, earthquake Geophysics, 57. https://doi.org/10.1029/ 2018RG000626 sequences and their geomorphic consequences alter mountain landscapes over both human and geologic time scales. Two recent events have attracted intense research into earthquake‐induced landslides and Received 1 OCT 2018 their consequences: the magnitude M 7.6 Chi‐Chi, Taiwan earthquake of 1999, and the M 7.9 Wenchuan, Accepted 22 APR 2019 China earthquake of 2008. Using data and insights from these and several other earthquakes, we analyze Accepted article online 7 MAY 2019 how such events initiate processes that change mountain landscapes, highlight research gaps, and suggest pathways toward a more complete understanding of the seismic effects on the Earth's surface. Plain Language Summary Strong earthquakes in mountainous regions trigger chains of events that modify mountain landscapes over days, years, and millennia. Earthquake shaking can cause many tens of thousands of landslides on steep mountain slopes. Some of these sudden slope failures can block rivers and form temporary lakes that can later collapse and cause huge floods. Other landslides move more slowly, in some cases in a stop‐start fashion during heavy rains or earthquake aftershocks. Debris from these landslides can clog channels, and during heavy rainfall, the debris can be transported downstream for many kilometers with catastrophic consequences. New landslides tend to happen more frequently than usual for months to years following an earthquake because the strong ground shaking has fractured and weakened the slopes. Other effects of large earthquakes can last, in various forms, over geologic time scales. Over the past two decades, our understanding of these issues has advanced because of the detailed study of the 1999 Chi‐Chi earthquake in Taiwan and the 2008 Wenchuan earthquake in China. We compile and discuss the results of research on these and other earthquakes and explain what we have learned, what we still need ©2019. The Authors. to know, and where we should direct future studies. This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs 1. Introduction License, which permits use and distri- bution in any medium, provided the Earthquake‐triggered landslides and their consequences are major hazards in mountains. The destructive original work is properly cited, the use is non‐commercial and no modifica- earthquakes in Taiwan (M 7.6, 1999), China (M 7.9, 2008), Nepal (M 7.8, 2015), and New Zealand (M 7.8, tions or adaptations are made. 2016) caused widespread landsliding and prompted researchers to study with increasing detail how FAN ET AL. 1 Reviews of Geophysics 10.1029/2018RG000626 earthquake‐triggered landslides erode landscapes. Early work by Simonett (1967) and Pearce and Watson (1983, 1986) recognized the importance of earthquakes in abruptly raising rates of erosion, sediment trans- port, and deposition. Detailed work on the 1999 Chi‐Chi, Taiwan earthquake (e.g., Dadson et al., 2004), pro- posed that earthquakes can change mountain landscapes instantaneously by triggering downslope movement of soils, debris, and rock landslides involving 103–1010 m3; more gradual flushing of these loose materials from the affected areas continues for some time after the triggering earthquake. Earthquake magnitude and depth are first‐order controls on the degree of landscape disturbance, modulated by the character of incoming seismic waves, topography, rock‐mass properties, groundwater conditions, and other factors (Fan, Scaringi, et al., 2018; Gorum et al., 2011). Seismic shaking is an instantaneous perturba- tion, but its effects attenuate, and the cumulative effects of earthquakes can leave a mark in the evolution of mountain landscapes (Hovius et al., 2011; Marc, Hovius, & Meunier, 2016). A cascade of processes actually takes place after a large continental earthquake (Figure 1). These processes bring differing degrees of hazard, which pose a risk when interacting with the human world. Spatial frequency distributions of earthquake‐triggered landslides are influenced by several factors, includ- ing source materials (i.e., the soil/regolith cover or the type of underlying intact bedrock), movement mechanisms (sliding, falling, flowing, or their combinations), ground‐motion characteristics, and sizes (in terms of planform area involved, depth, and volume displaced; Figure 1, red background). The shaking also can weaken slopes across the landscape and make them more prone to delayed failure (increased rate of occurrence). Days to years after the earthquake (blue background), landslide dams formed by earthquake‐ triggered landslides can breach and generate floods. Remobilizations and coalescence of landslide debris as a consequence of heavy rainfall can generate destructive debris flows. Years to decades later (yellow back- ground), floods can continue, albeit less frequently. Delayed slope failures also can occur, and slow processes such as river aggradation will become apparent as the earthquake‐generated debris progressively moves downstream. Description and discussion around these processes and their cause‐effect links form the struc- ture of this review, as presented in section 1.1. Many landslide disasters since 1900 have had an earthquake origin (Chen et al., 2012; Froude & Petley, 2018; Gorum et al., 2011; section 2.1). Investigating the patterns of these processes is essential for risk mitigation, emergency response, reconstruction, and increasing resilience (Das et al., 2018; Flentje & Chowdhury, 2018; Petley, 2011). Integrating these processes over longer time scales reveals the way earthquakes shape moun- tain belts and provides diagnostics for identifying past earthquakes in sediment and landforms. A large body of literature on specific aspects of the earthquake‐induced surface processes has grown over the past five decades. More than a thousand articles were published presenting case studies, models, and discus- sions on the impacts of the 2008 Wenchuan earthquake alone (Fan, Juang, et al., 2018). However, no com- prehensive reviews have covered thus far the complete role of earthquake‐induced landslides and their consequences across a variety of landscapes (and seismic patterns) and in short‐ to long‐term time scales. Only a small number of specialized reviews and meta‐analyses touching upon specific aspects of this topic have been published. The most widely recognized works, which were relevant for the preparation of our comprehensive review, are reported in Table 1. 1.1. Structure of the Review Seismic shaking
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