Scientific Framework

Three scientific modules form the underlying basis of GEM’s Global Earthquake Risk Model - Seismic Hazard, Seismic Risk and Socio-Economic Impact – as to allow for integral risk modelling and assessment.

Within GEM, seismic risk is defined as a product of seismic hazard (the probability of levels of ground shaking, resulting from earthquakes, within a given time span), seismic vulnerability (the probability of loss given a level of ground shaking), and exposure (the elements at risk, mainly buildings, critical infrastructure and humans). Risk tells us something about the extent of loss (damage, fatalities, casualties) that can be expected in a given location in the world. Risk can therefore be high in an area without significant probabilities of ground shaking, because it has an older, more vulnerable and densely populated building stock, and lower in an area with high levels of seismicity, but with well constructed structures that are sparsely inhabited.

Earthquakes however have an impact that goes beyond physical damage or casualties. Earthquakes can severely damage the economy and influence society and social well-being. Therefore, GEM’s Global Earthquake Risk Model will include methods [models, indicators, tools] for analysis and evaluation of the impacts of earthquakes on the short, medium and long term, on local and global scales. Insight into earthquake effects over time will directly support decisions on short-term needs after an event (relief, shelter), medium-term needs (recovery and reconstruction) and long term needs related to policies and activities aimed at risk mitigation.

Approach, gaps and uncertainty
The Global Earthquake Risk Model aims to cover the entire globe, as uniformly as possible, and to use models that incorporate the latest logic-tree approaches and that permit parameter changes so that seismic hazard and risk can be explored under different assumptions.

GEM is aware of the fact that complete uniformity of data will not be possible. First of all because GEM will not be able to incorporate all data for each single country in the world, and second of all not all datasets are uniform and some are even highly non-uniform.

GEM’s goal is therefore to collect observations to produce data coverage that is more uniform and complete than before. For most essential components of the model, GEM will create tools and standardized methods for obtaining and analyzing data, such as global building inventories and strategies for assessing the vulnerability of buildings, and GEM collaborators/affilated researchers will use these to tools to begin the process of assembling the needed datasets.

Our aim is that other researchers, agencies, and institutions will adopt and enhance these tools, and will help us to populate the datasets. Scientists may use the critical gaps in the model highlighted by GEM, to motivate and justify their proposals to funding agencies.