Scenario ensemble modelling of possible future earthquake impacts in Bhutan
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Scenario ensemble modelling of possible future earthquake impacts in Bhutan Tom R. Robinson1,2 Received: 28 April 2020 / Accepted: 22 June 2020 © The Author(s) 2020
Abstract Recent large earthquakes in the Himalaya have resulted in tens of thousands of fatalities, yet these events are thought to have had relatively moderate magnitudes for the region. Evidence suggests multiple events throughout the Himalaya in the last 1000 years have had M > 8.0 and at least two have had M > 8.5. Despite this, understanding of earthquake risk in the region is poorly constrained, particularly in Bhutan, where research on both past and future earthquakes is notably scarce. While recent work has clearly shown the potential for large earthquakes here, the impacts from potential future earthquakes in Bhutan are entirely unknown. This study attempts to address this by modelling the potential fatalities associated with a range of plausible earthquakes through a scenario ensemble analysis in order to inform contingency planning and preparedness. The results show that both the timing and location of future earthquakes are critical factors in determining the number of fatalities, with night-time earthquakes, and those located in the west of the country proving most fatal. The worst case involves ~ 9000 fatalities and results from an M8.5 earthquake directly beneath Bhutan. Nevertheless, at the local scale the number of fatalities appears to saturate at ~ M7.5, since larger earthquakes do not result in significantly larger modelled fatalities. This suggests that local-scale impacts approaching the worst case may be relatively common and emergency planning could focus on comparatively moderate-sized earthquakes since larger, less frequent events may not necessarily result in significantly more fatalities. Keywords Scenario ensembles · Earthquake impacts · Hazard and risk · Bhutan · Contingency planning
1 Introduction Earthquakes are amongst the most deadly natural hazards worldwide (Bilham 2004), and populations living in the Himalayan region are amongst the most at-risk to earthquake disasters globally (Robinson et al. 2019). In the last one thousand years, at least 15 large earthquakes are thought to have struck the region (Fig. 1), several of which are likely to * Tom R. Robinson [email protected] 1
School of Geography, Politics and Sociology, Newcastle University, Newcastle‑upon‑Tyne, UK
2
Department of Geography, Durham University, Durham, UK
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Natural Hazards
35°N
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20°N 70°E
75°E
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85°E
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95°E
Fig. 1 Known and inferred earthquakes with estimated magnitudes on the Main Himalayan Thrust (MHT) and surrounding faults in the last 1000 years compared to modern day urban populations. Inset: slip and earthquake magnitude potential on different segments of the MHT based on the time since last event, highlighting the Central Gap in western Nepal (500 + years) and the Bhutan Gap (300 + years). Adapted from Bilham et al. (2001) and Bilham (2019)
have had M > 8.0 (Feldl and B
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