In December 2018, at the conclusion of its second implementation phase, the Global Earthquake Model (GEM) Foundation released its first version of a map outlining the spatial distribution of seismic hazard at a global scale. The map is the result of an extensive, joint effort combining the results obtained from a collection of probabilistic seismic hazard models, called the GEM Mosaic. Together, the map and the underlying database of models provide an up-to-date view of the earthquake threat globally. In addition, using the Mosaic, a synopsis of the current state-of-practice in modeling probabilistic seismic hazard at national and regional scales is possible. The process adopted for the compilation of the Mosaic adhered to the maximum extent possible to GEM’s principles of collaboration, inclusiveness, transparency, and reproducibility. For each region, priority was given to seismic hazard models either developed by well-recognized national agencies or by large collaborative projects involving local scientists. The version of the GEM Mosaic presented herein contains 30 probabilistic seismic hazard models, 14 of which represent national or sub-national models; the remainder are regional-scale models. We discuss the general qualities of these models, the underlying framework of the database, and the outlook for the Mosaic’s utility and its future versions.

Abstract. A database of ∼250 active fault traces in the Caribbean and Central American regions has been assembled to characterize the seismic hazard and tectonics of the area, as part of the Global Earthquake Model (GEM) Foundation's Caribbean and Central American Risk Assessment (CCARA) project. The dataset is available in many vector GIS formats and contains fault trace locations as well as attributes describing fault geometry and kinematics, slip rates, data quality and uncertainty, and other metadata as available. The database is public and open source (available at: https://github.com/GEMScienceTools/central_am_carib_faults, last access: 23 March 2020), will be updated progressively as new data become available, and is open to community contribution. The active fault data show deformation in the region to be centered around the margins of the Caribbean plate. Northern Central America has sinistral and reverse faults north of the sinistral Motagua–Polochic fault zone, which accommodates sinistral Caribbean–North American relative motion. The Central Highlands in Central America extend east–west along a broad array of normal faults, bound by the Motagua–Polochic fault zone in the north and trench-parallel dextral faulting in the southwest between the Caribbean plate and the Central American forearc. Faulting in southern Central America is complicated, with trench-parallel reverse and sinistral faults. The northern Caribbean–North American plate boundary is sinistral off the shore of Central America, with transpressive stepovers through Jamaica, southern Cuba and Hispaniola. Farther east, deformation becomes more contractional closer to the Lesser Antilles subduction zone, with minor extension and sinistral shear throughout the upper plate, accommodating oblique convergence of the Caribbean and North American plates.

The design of critical facilities needs a targeted computation of the expected ground motion levels. The Trans Adriatic Pipeline (TAP) is the pipeline that transports natural gas from the Greek-Turkish border, through Greece and Albania, to Italy. We present here the probabilistic seismic hazard analysis (PSHA) that we performed for this facility, and the deaggregation of the results, aiming to identify the dominant seismic sources for a selected site along the Albanian coast, where one of the two main compressor stations is located. PSHA is based on an articulated logic tree of twenty branches, consisting of two models for source, seismicity, estimation of the maximum magnitude, and ground motion. The area with the highest hazard occurs along the Adriatic coast of Albania (PGA between 0.8 and 0.9 g on rock for a return period of 2475 years), while strong ground motions are also expected to the north of Thessaloniki, Kavala, in the southern Alexandroupolis area, as well as at the border between Greece and Turkey. The earthquakes contributing most to the hazard of the test site at high and low frequencies (1 and 5 Hz) and the corresponding design events for the TAP infrastructure have been identified as local quakes with MW 6.6 and 6.0, respectively.

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