Abstract

ROJAS VERA, Emilio A et al. Paleoseismic evidence in the Loncopué trough and the Agrio fold and thrust belt (Huecú depocenter), Neuquén Province. Rev. Asoc. Geol. Argent. [online]. 2010, vol.67, n.2, pp.163-176. ISSN 0004-4822.

Liquefacted lacustrine sediments were identified at the Quaternary El Huecú depocenter, located in the central part of the retroarc Loncopé trough at the northwestern Neuquén sector. These were interpreted as seismites based on their morphological characteristics, as well as their neotectonic setting. Additionally, over the western Agrio fold and thrust belt, other similar deposits were identified. Finally, fractured gravels associated with clastic dykes are developed at the eastern Loncopué fault system between the previous two occurrences. A remote source is a possibility for the paleoseismic evidence. Particularly, the February 27th of 2010 earthquake, the fifth earthquake in magnitude since the instrumental period of time, showed that even though energy arrives rather attenuated at the retroarc zone, is sufficient to generate the described liquefacted deposits. On the other hand, only local and strong earthquakes could generate the intruded and fractured gravels. Assuming a common and local seismogenic source for the described occurrences and using known empirical formulae proposed by other authors, two areas were outlined as potential sites for seismic triggering (the El Huecú basin and the inner Agrio fold and thrust belt). Its intersection corresponding to the eastern Loncopué fault system appears as the main potential source for seismic activity, which is compatible with previous neotectonic studies performed in this region and the occurrence of fractured gravels and clastic dykes in the area.

Keywords : Paleoseismology; Neotectonics; Loncopué trough; Seismites; Andes.

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