De la neotectónica a la amenaza sísmica en América Latina y el Caribe

Abstract

Today it is understood that the seismic risk, as well as any type of risk, is proportional to the disastrous combination of the seismic threat and the vulnerability of the exposed systems. Considering that the seismic threat is of natural origin, therefore not modifiable or controllable by man to any extent - unlike other threats that are anthropic or generated by man himself (eg nuclear explosions, seismicity induced by dams or reservoirs of water, etc.) if they are-, risk reduction is achieved both by increasing resilience (a system's own capacity to recover from an adverse event) and by reducing the exposure of potentially exposed systems. However, it should be noted that risk can be better characterized and quantified if the threat is better defined and known, even though it cannot be controlled. That is why the seismic threat needs to be the best bounded, measured and defined, to the extent of the available information, in order to reduce uncertainties to the maximum. It then requires that the seismic activity of the region under study be studied in detail, which also implies identifying and characterizing the generating sources of these earthquakes (seismogenic faults); that is, the geological faults responsible for such seismicity (seismotectonic association; Figure 1). It is customary in seismic hazard studies to study both aspects (source faults and seismicity) in a radius of at least 200 km; distance resulting from the attenuation of seismic energy as it propagates through the medium. So it is understood that the seismic energy released during most large earthquakes is expected to be attenuated to low hazard levels at that distance. The built environment located in sedimentary basins filled with soft or little consolidated sediments, such as the cases of Mexico City and Caracas, probably escape this practice, due to wave amplification effects as a site effect, which could be excited by large shallow or shallow earthquakes. subduction, with epicenters beyond that distance prescribed by practice. Consequently, it is necessary to retrace the seismic history –or earthquake chronology, which is the sum of the instrumental, historical and pre-historical earthquakes that make up the entire seismic activity (Audemard, 2019) - of the region surrounding the site. subject to a seismic hazard assessment (EAS; in English, Seismic hazard Assessment -SHA-), in the most complete way, as well as extensive in the time possible, in order to determine two fundamental parameters when calculating said estimate: the Maximum probable earthquake and the return period of large earthquakes with destructive capacity, for each of the identified faults, or their individual segments if they are defined. Given that these EAS can be addressed by two approaches, probabilistic and deterministic (or various combinations of both), the longest in time is the evaluated period, the statistical evaluations of both parameters indicated above - known under the term of seismogenic potential- , they will be more robust and reliable to estimate the seismic threat.