National Society for Earthquake Technology

Landslides are one of the most damaging disasters and have killed tens of thousands of people over the 21st century. Slow-moving landslides (i.e., those with surface velocities on the order of 10-2-101 m a-1) can be highly disruptive but are often overlooked in hazard inventories due to their subtle surface signatures and slow movement. Here, we discuss an approach to automatically map slow-moving landslides using feature tracking of freely- and globally-available Sentinel-2 optical satellite imagery.We evaluate this method through case studies from different environments in the USA, Chile, Italy, and Nepal. Our workflow identifies both known landslides and previously unknown slow-moving landslides in these case studies across very different geographical environments. In particular, in a test case on the well-documented Slumgullion earthflow, our workflow successfully delineates the active portion of the earthflow with velocity magnitudes consistent with field measurements. In another test case on the margin of the Southern Patagonian Icefield, Chile, we identified a very large (>6 km2) composite landslide in the eastern lateral moraine of Glacier Occidental, part of which catastrophically collapsed onto the glacier in early 2023. Finally, we tested our tool to the Ponzano landslide in central Italy which failed catastrophically in 2017.We are able to detect slow-moving landslides in complex environments using 10-m resolution globally available satellite imagery, all without any manual intervention. Taken together, this means that our workflow can be applied to any region on Earth, regardless of the availability of prior information. We leverage this workflow to conduct a preliminary national-scale survey of slow-moving landslides in Nepal, identifying over 10,000 deforming hillslopes across the country, many of which are populated. Improved mapping of the spatial distribution and surface displacement rates of slow-moving landslides will improve our understanding of their role in the multi-hazard chain and can direct detailed investigations into their dynamics.Figure: Large slow-moving landslide complex in the lateral moraine of Glaciar Oriental, Chilean Patagonia detected using our workflow.

A review of landslide inventories provides an essential assessment of the state of knowledge around landslide hazard and can guide the focus of future studies. This is especially true in Nepal, which is highly prone to landslides, but lacks a comprehensive overview of landslide occurrence nationally. Here, we compile a database of 117 landslide inventories for Nepal released between 2010 and 2021. We review how these existing inventories shape our understanding of landsliding in Nepal and discuss how future research efforts could mitigate current challenges. We find that 40% of the country was only manually mapped once across the study period, and, crucially, these areas did not always correspond with areas of low landslide susceptibility. Instead, existing landslide inventories typically focus on specific areas, such as the region affected by the 2015 Gorkha Earthquake and major highway corridors. We also extrapolated the individual inventory characteristics from within this unique database to infer a national-scale areal density of 0.05 landslides per km2, equating to 6000 landslides across the country. This extrapolated value provides a baseline for future national-scale studies, especially for inventories created through automated mapping approaches. Our review highlights the importance of expanding the footprint of landslide inventories in Nepal to include regions with low mapping coverage and the need for inventories to be openly available, with clear protocols to enable inter-comparison. Whilst our review has focused on Nepal, these findings are likely to be relevant in other landslide-prone countries and our recommendations are intended to be applicable elsewhere.

The present study undertakes a comparative analytical examination of seismic analysis standards in Nepal, focusing on NBC 105:1994 and the updated NBC 105:2020, encompassing both the Ultimate Limit State (ULS) and Serviceability Limit State (SLS). Employing a regular Reinforced Concrete (RC) apartment building in Pokhara as a case study, the geometric and sectional configurations of structural elements are intentionally kept consistent for comparison. The analysis involves creating a 3D model using ETABS version 19, encompassing linear static, Equivalent Static (ES), and linear dynamic Response Spectrum (RS) analyses, followed by nonlinear static (pushover) analysis. The results highlight substantial differences between the two codes. Base shear from NBC 105:2020 is notably higher, being 28.59% ULS and 22.74% SLS greater than NBC 105:1994. The scale factor for combined response design values is significantly lower in both X and Y directions for NBC 105:2020. Story shear is extended by 33% ES and 37% RS with NBC 105:2020 compared to NBC 105:1994. Maximum design displacement and Inter-Story Drift (ISD) are markedly higher with NBC 105:2020, indicating its more severe seismic parameters. This study emphasized the enhanced seismic resilience provided by NBC 105:2020, particularly evident in increased base shear, reduced design scale factors, and higher values for story shear, displacement, and ISD. These findings contribute valuable insights into the seismic design improvements introduced in Nepal's seismic codes after the Gorkha Earthquake in 2015.

Disaster impact metrics (DIMs) are key outputs of natural-hazard risk models/assessments that provide a tangible way of communicating risk. However, typical DIMs are limited in that they tend to capture only direct damage/economic losses, be specifically designed for developed countries, account for just one snapshot in time, and be characterised for individual assets rather than systems. These shortcomings somewhat stem from a lack of understanding around the bespoke requirements of different stakeholders concerning disaster impact/risk assessments. Addressing these limitations, we propose a toolbox for characterising context-specific DIMs that capture relevant stakeholder priorities/requirements. The toolbox includes: (1) a comprehensive, holistic pool of DIMs developed from a literature review and a conceptual representation of societal dependencies; and (2) a stakeholder-centred framework for facilitating the appropriate selection of DIMs from this pool. We demonstrate the framework for Kathmandu, Nepal, revealing that the relative importance of a given disaster impact can change for different stakeholder groups and spatio-temporal dimensions. Impacts related to direct damage/economic losses are not the most crucial concern of the considered stakeholders. Higher priority is placed on characterising accessibility impacts around utilities and social networks, for instance. This work contributes to advancing the usefulness of natural-hazard risk assessments for important decision-making.

<p>The Nepal Himalayas result from the India-Eurasia collision and the actual shortening is accommodated by a detachment ramp, the Main Himalayan Thrust (MHT). Separating high-grade metamorphic rocks from the Greater Himalayan Sequence to the north and low-grade metamorphic rocks from the Lesser Himalayan Sequence to the south, the Main Central Thrust (MCT) shear zone, is related to the MHT at depth where large Himalayan earthquakes nucleate. The MCT zone occurs from Far-Western to Eastern Nepal, associated at mid-crustal depth with active seismicity and high electrical conductivity; it exhibits carbon-rich rock layers and numerous active hydrothermal systems. Here, based on a multidisciplinary approach that includes geology, geochemistry and geophysics, we study the various sulphur and carbon signatures in the MCT zone in the Nepal Himalayas. First, we characterise the upper LHS rocks that include alternation of graphite-rich mica-schists (the so-called “black schists”) and carbonates (mainly siliceous dolomite). In the laboratory, we determine organic and inorganic carbon contents, as well as complex electrical conductivity. Second, we concentrate on numerous thermal springs in which we measure dissolved carbon and sulphur concentrations and their isotopic compositions (δ<sup>13</sup>C and δ<sup>34</sup>S). Third, we study the surface gaseous emissions, directly observed in the vicinity of hot springs, with the measurements of carbon dioxide (CO<sub>2</sub>) and hydrogen sulphide (H<sub>2</sub>S) fluxes and isotopic compositions. By comparing the signatures of carbon and sulphur sequestration and carbon and sulphur release at a large spatial scale, our work provides insights into the carbon source-to-sink duality of large orogens, the metamorphic processes and the carbon and sulphur geochemical cycles.</p><p> </p>

This study reports the geostatistical analysis of a set of 40 single-station horizontal-to-vertical spectral ratio (HVSR) passive seismic survey data collected in the Kathmandu basin (Nepal). The Kathmandu basin is characterized by a heterogeneous sedimentary cover and by a complex geo-structural setting, inducing a high spatial variability of the bedrock depth. Due to the complex geological setting, the interpretation and analysis of soil resonance periods derived from the HVSR surveys is challenging, both from the perspective of bedrock depth estimation as well as of seismic-site effects characterization. To exploit the available information, the HVSR data are analyzed by means of a geostatistical approach. First, the spatial continuity structure of HVSR data is investigated and interpreted taking into consideration the geological setting and available stratigraphic and seismic information. Then, the exploitation of potential auxiliary variables, based on surface morphology and distance from outcropping bedrock, is evaluated. Finally, the mapping of HVSR resonance periods, together with the evaluation of interpolation uncertainty, is obtained by means of kriging with external drift interpolation. This work contributes to the characterization of local seismic response of the Kathmandu basin. The resulting map of soil resonance periods is compatible with the results of preceding studies and it is characterized by a high spatial variability, even in areas with a deep bedrock and long resonance periods.

The 25 April 7.8 magnitude Gorkha earthquake and subsequent aftershocks, including the 7.3 magnitude earthquake in Dolakha, severely damaged or destroyed nearly 900,000 buildings and approximately 2.3 million people continue to be displaced. We conducted 284 household surveys in 177 shelter sites spanning 27 Municipalities/VDCs and 7 districts. The aim of the survey was to analyze the shelter response situation in both urban and rural areas with a view on emerging factors influencing the decision processes of displaced households seeking shelter and temporary housing. It was found that in-place sheltering close to damaged homes was favored by many residents in both urban and rural areas as many preferred to stay close to their homes, food reserves, livelihoods and social ties. The experience from this event shows that spontaneous sheltering behavior and participatory management of these sites should be accommodated and supported in the shelter response strategy.

Disaster education allows community members to initiate pre-disaster measures at the individual level. The National Society for Earthquake Technology (NSET) has initiated a school safety program in selected government schools in Nepal, one of the most disaster prone countries. This study outlines the current condition of disaster education in Nepal, identifies teachers’ levels of awareness and evaluates the effect of NSET's work. A survey of 130 teachers was conducted in over 40 schools in which it was found that while a level of disaster education in Nepal is widespread, it has not been implemented systematically but depends on the awareness of individual teachers. More teachers in NSET project schools provided disaster education than in the typical government and private schools that were observed. However, the quality of education provided was found to be the same. The teaching focused particularly on the effects of disasters in which the teachers had personal experience. These topics were often covered even if they were not included in the textbooks. The majority of teachers surveyed reported a need for curriculum development in this area. However, considering the results listed above, it can be considered that teacher training is the most important step to improve disaster education in Nepal.