periods of the experiments and long time after, the seismicity dynamics were a lot more regular than usual. Risk analysis Risk factors Risk is defined as the probability of being impacted from an event in the future. Seismic risk is generally estimated by combining the seismic hazard with the exposure and vulnerability at a site or over a region. The hazard from earthquakes depends on the proximity to potential earthquake sources, and the rates of occurrence of different magnitude earthquakes for those sources, and the propagation of seismic waves from the sources to the site of interest. Hazard is then represented in terms of the probability of exceeding some level of ground shaking at a site. Earthquake hazards can include ground shaking, liquefaction, surface fault displacement, landslides, tsunamis, and uplift/subsidence for very large events (ML > 6.0). Because induced seismic events, in general, are smaller than ML 5.0 with short durations, the primary concern is ground shaking. Ground shaking Ground shaking can result in both structural and nonstructural damage to buildings and other structures. It is commonly accepted that structural damage to modern engineered structures happens only in earthquakes larger than ML 5.0. In seismology and earthquake engineering, ground shaking can be measured as peak ground velocity (PGV), peak ground acceleration (PGA) or spectral acceleration (SA) at a building's period of excitation. In regions of historical seismcity where buildings are engineered to withstand seismic forces, moderate structural damage is possible, and very strong shaking can be perceived when PGA is greater than 18-34% of g (the acceleration of gravity). In rare cases, nonstructural damage has been reported in earthquakes as small as ML 3.0. For critical facilities like dams and nuclear plants, the acceptable levels of ground shaking is lower than that for buildings. Probabilistic seismic hazard analysis Extended reading – An Introduction to Probabilistic Seismic Hazard Analysis (PSHA) Probabilistic Seismic Hazard Analysis (PSHA) is a probabilistic framework that accounts for probabilities in earthquake occurrence and the probabilities in ground motion propagation. Using the framework, the probability of exceeding a certain level of ground shaking at a site can be quantified, taking into account all the possible earthquakes (both natural and induced). PSHA methodology is used to determine seismic loads for building codes in both the United States and Canada, and increasingly in other parts of the world, as well as protecting dams and nuclear plants from the damage of