Evolution of coseismic and post-seismic landsliding after the 2015 Mw 7.8 Gorkha earthquake, Nepal

Abstract

Coseismic landslides represent a major cascading hazard associated with high-magnitude earthquakes in mountainous environments (Fan, Scaringi, Domènech, et al., 2019;Fan, Scaringi, Korup, et al., 2019). The widespread landsliding observed in many recent large continental earthquakes has led to substantially higher death tolls when compared to earthquakes without landslides (Budimir et al., 2014), disruption to infrastructure (Aydin et al., 2018;Bird & Bommer, 2004), and the mobilization and transport of large volumes of sediment (M. Y. F. Huang & Montgomery, 2012;Wang et al., 2015). Increased interest in understanding the spatial distribution, impacts, and timing of coseismic landslides in recent decades has resulted in the production of a growing number of coseismic landslide inventories (Tanyas et al., 2017). In contrast, despite growing evidence for the persistence of enhanced landslide rates and the consequent long-term impacts of coseismic hillslope damage in the years to decades after a major earthquake (e.g., Dadson et al., 2004;Hovius et al., 2011;Parker et al., 2015), our current understanding of the post-seismic evolution of landslides is limited. As a result, we remain incapable of anticipating the spatio-temporal evolution of landslide hazard after a large earthquake, which frustrates our ability to inform response, recovery, and reconstruction (e.g., Robinson et al., 2017;Williams et al., 2018), and limits understanding of the long-term role of earthquakes in the overall mountain sediment cascade.A standard approach to tracking post-seismic landsliding is to develop multi-temporal landslide inventories, usually by mapping from airborne or satellite imagery. This is a time-consuming and potentially expensive Abstract Coseismic landslides are a major hazard associated with large earthquakes in mountainous regions. Despite growing evidence for their widespread impacts and persistence, current understanding of the evolution of landsliding over time after large earthquakes, the hazard that these landslides pose, and their role in the mountain sediment cascade remains limited. To address this, we present the first systematic multi-temporal landslide inventory to span the full rupture area of a large continental earthquake across the pre-, co-and post-seismic periods. We focus on the 3.5 years after the 2015 M w 7.8 Gorkha earthquake in Nepal and show that throughout this period both the number and area of mapped landslides have remained higher than on the day of the earthquake itself. We document systematic upslope and northward shifts in the density of landsliding through time. Areas where landslides have persisted tend to cluster in space, but those areas that have returned to pre-earthquake conditions are more dispersed. While both pre-and coseismic landslide locations tend to persist within mapped postearthquake inventories, a wider population of newly activated but spatially dispersed landslides has developed after the earthquake. This is particularly important for post-earthquake recovery plans that ...

Temporal Variations in Landslide Distributions Following Extreme Events: Implications for Landslide Susceptibility Modeling

“…This result is similar to those of Kincey et al. (2021) who found significant changes in the characteristics and distributions of coseismic and monsoon‐triggered landslides in Nepal across the period 2014–2018. But what causes these changes?…”

“…This earthquake induced maximum PGAs of 250 cm/s 2 , caused over 8,000 fatalities and reportedly triggered over 240,000 coseismic landslides (Roback et al., 2018; Takai et al., 2016). The Gorkha earthquake also caused enhanced rates of post‐earthquake monsoon‐triggered landslides (Marc et al., 2019), with high densities of post‐earthquake landslides shifting upslope and northward (Kincey et al., 2021). This region has also been impacted by two cloud outburst storms over the past 30 yr, in 1993 (Dhital, 2003) and in 2002 (Dahal & Hasegawa, 2008).…”

A closer look at factors governing landslide recovery time in post-seismic periods

“…This might be an issue for Finisterre and Chi-Chi cases where landslides were mostly mapped by Landsat images (see supplementary materials of Marc et al, 2015). Moreover, differentiation of reactivated landslides from remobilization of debris within individual landslide scars could not be possible without high-resolution images and therefore, identification of reactivated landslides may not be possible if high-resolution images are not available and could also introduce uncertainty in landslide recovery time (Kincey et al, 2021).…”

“…In the last two decades, we have expanded our insight regarding post-seismic landslide processes. Several multi-temporal post-seismic landslide inventories have been compiled and made available showing that earthquakes contribute to increase landslide susceptibility in post-seismic periods (Tang et al, 2016;Zhang et al, 2016;Fan et al, 2018;Chen et al, 2020;Kincey et al, 2021;Tanyaş et al, 2021a).…”

“…As it is seen from the summary above, several studies in the literature examine the concept of landslide recovery time from different perspectives and provide insight into the concept (e.g., Chen et al, 2020;Fan et al, 2018;Marc et al, 2015;Tian et al, 2020). However, there is still considerable confusion and debate about landslide recovery time (Kincey et al, 2021). In most cases, even for the same earthquakes, the suggested landslide recovery times are not consistent with each other.…”