Neotectonics, seismicity and paleoseismicity.

LAURA PERUCCA Y HUGO BASTIAS

Late Cenozoic of Patagonia and Tierra del Fuego, Development in Quaternary Science Series

Elsevier

Lugar: Inglaterra; Año: 2008; p. 73 - 94

There are few papers on the neotectonics and seismicity of the farthest end of South America. However, according to INPRES – CIRSOC (Instituto Nacional de Prevención Sísmica-Centro de Investigaciones de los Reglamentos Nacionales de Seguridad para las Obras Civiles) 103 rulings, five areas of increasing hazard, from 0 to 4, have been established for Argentina ; the  Archipelago of Tierra de Fuego is located in an area of high hazard with a risk  coefficient slightly inferior to that of the Cuyo region (in the highest Andes of western Argentina), and Salta and Jujuy (northwestern Argentina), whereas the province of Neuquén, in northwestern Patagonia, and the western part of Chubut province are found in an area of moderate seismic hazard. In all events, seismicity has only been partially investigated due to limited geophysical and geological field studies, and in general, to the lack of sufficient and appropriate seismological and geophysical equipment (which was non-existing during the XIXth. Century and part of the XXth.). Only a low to moderate seismicity (magnitudes lower than 5.6 Richter Scale) is known  for this region, mainly through readings of international networks, and only in a few occasions through local networks. The relationship between this seismicity and destructive earthquakes is important to better understand the functioning of active tectonics in the region. Due to the extended recurrence period between intercontinental earthquakes, the short temporary intervals that historical and instrumental seismicity provide need to be extended, through paleoseismological studies of the Pleistocene-Holocene seismic deformations, which together with the maps of recent deformation and the analysis of low to moderate seismicity and the characteristics of local and regional active faults would allow an evaluation of the seismic hazard in this region in a more real sense.   There is a close relationship between the greater structures as defined in this paper, and the localization of seismic events, specially regarding the separation of environments with different seismic activity levels. Apparently, these greater structures would also bound some of the volcanic settings, mainly Neogene in age, and the different areas with Neogene tectonic activity. Understanding these alignments like borders or transitional limits among cortical regions that show different morphostructural aspects, four seismotectonic regions were determined, in which the behavior of the efforts during the present tectonic régime can be interpreted as characteristic of that region.  The number and the limits of these areas could be changed in the future, as more information on the distribution of seismicity, volcanism and of the active faulting in each one of them is obtained. Key words: Patagonia, seismicity, seismotectonic regions, active faulting