Earthquakes are the most devastating, unpredictable, and frightening natural dangers. Destructive earthquakes are not common events, especially in areas of moderate of low seismic activity, but they have a huge destruction potential in the environment and are a serious threat for life, implying enormous social and economical costs. Earthquakes are unavoidable events that happen suddenly and cannot be predicted by science yet. Nevertheless, what can be predicted is their effect over the environment. The quantification of the probable damages and losses (physical, economical, and social) caused by an earthquake is what we define as seismic risk.
As the damage is a result from the interaction between the seismic destruction potential (seismic danger) and the vulnerability of the exposed elements liable to the damage, it is possible to reduce the risk by reducing this vulnerability and the exposition to the seismic action. Once the risk evaluations estimate that there is an unacceptable risk in certain areas, it becomes urgent to take preventive and protective measures that can diminish the destructive effect of an earthquake, especially to reduce the potential lethal and economic impact, and to face a fast-as-possible recovery after the event. Seismic-resistant constructions and disaster plans are the best way to reduce damages and injuries.
The strategies and actions have to be taken individually and collectively. They have to build upon a basic knowledge on earthquakes and their effects, as well in the potential dangers, vulnerability and seismic risk of the area. In this work we briefly address: 1)the direct (permanent floor deformations, intense vibration of the area) and indirect (cracks, subsidence, liquefaction, slides, and human and construction damages) seismic effects; 2) which are the the elements that influence the seismic threat of a location, including the local amplification effects and how to quantify the destruction potential of an earthquake in the field; 3) which are the intrinsic characteristics that make vulnerable each element of risk, the typical location of damages in buildings after a seismic actions, some basics of the seismic-resistant constructions, and reinforcement efforts over existing constructions; and 4) how to characterize and locate the seismic risk of an area, and the implications that this has.
We also offer some guidance on effective measures to reduce the seismic risk; some of them on the long-medium term such as locating the seismic risk and spatial management, urban plans based in seismic micro-location, the application of seismic-resistant principles in the constructions, the monitoring and preservation of these constructions, and the reinforcement of all previous constructions and infrastructures to make them as seismic-resistant as possible in order to have an acceptable seismic risk; and other on the short-very short term such as the estimation of seismic scenarios, alert systems and early estimation of damage potential, education and training of the population on seismic security, informing them of the seismic risk, emergency and management plans, rapid intervention and victim cares, emergency procedures in the affected areas, fast evaluation of the buildings' post-earthquake habitability, and recovery of services. Lastly, we indicate a number of preventive measures to know what to do before, during and after the earthquake.