Abstract

RODRIGUEZ, Evelyn; LINKIMER, Lepolt  and  MONTERO, Walter. Neotectonic of the Cipreses fault, Costa Rica. bol.geol. [online]. 2019, vol.41, n.2, pp.15-33.  Epub May 30, 2019. ISSN 0120-0283.  https://doi.org/10.18273/revbol.v41n2-2019001.

The Cipreses fault is located in the central part of Costa Rica, in the most populated region of the country. In this paper, the Cipreses fault is analyzed based on geomorphological, geological, and seismological observations.The main geomorphological evidences found are: scarps, terraces, river incisions, and deflected and dammed streams. In the vicinity of the fault, there are three main Pleistocene geologic units: tuff, breccia, and andesitic lavas. These units were found displaced by the fault in an outcrop. From the seismological analysis, we conclude that the instrumental seismicity is low, but at least one earthquake in 2010 (4.1 Mw) was originated in the Cipreses fault. The focal mechanism solution for this event indicates a thrust fault with a nodal plane of dip direction N30°E/35° in agreement with the fault plane found in the field and the geomorphological observations. Based on a conceptual model for the faulting, we interpret that the Cipreses fault corresponds to a master fault that propagates to the surface along two fault segments named Pinares and Guayabos. The displacements of these faults made two anticlinal folds, which are expressed at the surface as prominent scarps. Based on the evidences found we conclude that the Cipreses fault is an active thrust fault with a surface expression of 14 km and with the seismic potential of magnitude Mw 5.9-6.5.

Keywords : Costa Rica; active fault; Cipresses Fault; neotectonics..

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