The Mosaic: A dynamic framework
The GEM Global Seismic Hazard Mosaic is a database of national and regional seismic hazard models all described using the OpenQuake (OQ) engine data format. The mosaic consists of hazard models developed by various institutions, within collaborative projects, and by GEM Foundation scientists. It includes models originally developed using the OQ engine, and models originally implemented in other software formats that have been converted into the OQ engine.
The mosaic has a dynamic structure that allows for easily incorporating new models as they become available. This is facilitated by the use of OQ, GEM's flexible seismic hazard and risk calculation software. The result is a dynamic database of hazard models representing the most recent and openly accessible information for every area. Meanwhile all previous versions of models are kept in the database and remain fully compatible with OQ.
In December 2018, GEM achieved global coverage with a total of 30 national and regional seismic hazard models. With global coverage, GEM produced its first global seismic hazard map - a milestone originally achieved by the Global Seismic Hazard Assessment Program (GSHAP; Giardini et al., 1999) - and the first fully transparent and open global seismic hazard model.
Global Seismic Hazard Map
The GEM Global Seismic Hazard Map version 2018.1 (Pagani et al., 2018) depicts the geographic distribution of the Peak Ground Acceleration (PGA) with a 10% probability of being exceeded in 50 years, computed for reference rock conditions (shear wave velocity, Vs30, of 760-800 m/s). OQ was used to calculate the hazard values for every model in the GEM mosaic.
The GEM Global Seismic Hazard Map, v. 2018.1. Download here!
For the construction of the GEM Global Seismic Hazard Map, a smoothing methodology was applied to homogenise hazard values along the model borders. A zone of ~150 km was used to blend the hazard results of adjacent models.
For regions covered by more than one hazard model, the hazard results associated with the most recently developed hazard model were used in the GEM Global Seismic Hazard Map.
To achieve a consistent reference site condition at a global scale, it was necessary to modify the original ground motion prediction equations (GMPEs) for a small number of models. This was the case for GMPEs that were originally derived for a reference site condition other than Vs30 = 760-800 m/s, but do not vary with the Vs30 parameter. Modifications to original GMPEs have been noted in the model pages.
Giardini, D., G. Grünthal, K.M. Shedlock and P. Zhang (1999). The GSHAP Global Seismic Hazard Map, Annali di Geofisica, 42 (6), 1225-1230; doi:10.4401/ag-3784.
Pagani, M., Garcia-Pelaez, J., Gee, R., Johnson, K., Poggi, V., Styron, R., Weatherill, G., Simionato, M., Viganò, D., Danciu, L., Monelli , D. (2018). Global Earthquake Model (GEM) Seismic Hazard Map (version 2018.1 - December 2018), doi.org/10.13117/GEM-GLOBAL-SEISMIC-HAZARD-MAP-2018.1