Drivers of Earthquake Damage and Losses: a Global Perspective on Where and Why Seismic Risk is High

We know more about earthquake processes, vulnerability modelling and characterization of the built environment than ever before. Yet, earthquake losses and casualties continue to increase, even in countries where modern seismic design regulations have been introduced decades ago. In this study we investigate the drivers of earthquake damage and losses using the global seismic hazard and risk model developed by the Global Earthquake Model (GEM) Foundation and its partners, as well as data from fatal earthquakes since 1950. We isolate specific parameters that can influence the severity of the ground shaking, the vulnerability of the building stock, and the spatial distribution of the population. These include the prevalence of soft soils, the average seismic hazard in each country, the likelihood of experiencing extreme ground shaking, the occurrence of earthquake-triggered hazards (i.e., liquefaction, landslides and tsunamis), the time of the event, the proximity of megacities to active faults, the percentage of specific types of construction, and some socio-economic factors. We compare these underlying parameters and the estimated or observed seismic risk between different countries and identify specific patterns that systematically exacerbate the overall impact. We observe that high economic losses are frequent in countries with well-established seismic regulations not only due to the high replacement/repair costs, but also due to the high prevalence of commercial and industrial facilities and complex infrastructure. On the other hand, high fatality risk is frequent in countries whose building stock is comprised of non-engineered buildings with heavy roofs and floors. Another relevant observation is that although ground shaking is overwhelmingly the main cause of damages and losses, under specific geological and demographic conditions, the impact of tsunamis, landslides and liquefaction phenomena can be devastating. Lessons drawn from these observations and patterns can be useful to understand how the impact of earthquakes can be better assessed, reduced, and managed.