Scenario ensemble modelling of possible future earthquake impacts in Bhutan

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.

Use of scenario earthquakes for seismic hazard assessment in low-seismicity, stable continental regions: A case study from Indiana, USA

“…While the default Hazus inventories do not provide enough detail for a complete analysis of this type, a municipality or state could update the building, infrastructure, and population inventories in Hazus to get more accurate estimates, especially for critical infrastructure or areas of particular interest. Another sort of hybrid PSHA/DSHA approach is to combine a suite of ground shaking and loss estimation scenarios for plausible earthquake sources with infrastructure and population vulnerability data to estimate the overall risk for an area, as Robinson (2020) and Robinson et al (2018) did for Nepal and Bhutan. Because earthquakes in the Central and Eastern United States are infrequent and there is limited prehistoric and historic seismic activity, running a suite of plausible scenarios could help identify the sites of significant risk across scenarios, and special vulnerabilities associated with essential facilities (e.g.…”

“…the Earthquake Engineering Research Institute (EERI)) and local stakeholders have conducted detailed scenarios that analyze both the hazards due to ground shaking and the risk associated with exposure and vulnerability for southern California near Los Angeles (the Great ShakeOut; see Jones et al, 2008; Porter et al, 2011), northern California near San Francisco (the HayWired scenario; see Detweiler and Wein, 2018), and the California–Mexico border near San Diego–Tijuana (EERI, 2020). Robinson (2020) and Robinson et al (2018) used ensembles of deterministic scenarios, along with population, infrastructure, and vulnerability inventories, to assess risk due to various possible seismic sources in Nepal and Bhutan. Deterministic scenarios have been widely used for assessing potential impacts of a NMSZ earthquake (e.g.…”

Application of Scenario Earthquakes for Analysis of Seismically Triggered Landslide Hazard: A Case Study in Costa Rica

“…Past studies have used a number of different methods to compute ground shaking and impact estimates for hypothetical scenario earthquakes. Robinson et al (2018) and Robinson (2020) predicted ground shaking for scenario earthquake ensembles consisting of 90 different seismic events in Nepal and Bhutan, which were then combined with building type and population data to predict potential fatality and impacts to infrastructure. The USGS ShakeMap system has also been used to create scenario earthquakes at multiple locations of interest across the United States, including a M 7.0 earthquake on the Hayward Fault to examine potential impacts from ground shaking in the San Francisco Bay area of California (Detweiler and Wein, 2017).…”

Paleoseismological Findings at a New Trench Indicate the 1714 M8.1 Earthquake Ruptured the Main Frontal Thrust Over all the Bhutan Himalaya

“…The segment of the in eastern Bhutan is thought to host a potential slip of more than 10-12 m (Bilham, 2019;Robinson, 2020), the greatest in the Himalayas, implying high seismic hazard (Stevens et al, 2020). Conversely, the Bhutanese Himalaya experience fewer instrumental earthquakes than the central and western Himalayas (Gahalaut et al, 2011;Stevens and Avouac, 2015;Jayangondaperumal et al, 2018).…”