Abstract

BEAUPERTHUY U, Luis D; FRANCISCO BONIVE, Luis F; CARABALLO, Américo Montilla  and  ROJAS, Jorge. Analysis of the seismic activity during august 11 to 18, 2008, near Cumaná city, Venezuela. Rev. Fac. Ing. UCV [online]. 2011, vol.26, n.2, pp.7-16. ISSN 0798-4065.

The seismic activity close to Cumaná city, Venezuela, during August 11 to 18, 2008, and recorded by the local seismic CSUDO network, is analyzed in order to identify the activated fault plane and evaluate its geometrical and mechanical parameters. The activity started with a (main) quake of coda magnitude 5.1, followed by 13 registered events with coda magnitudes between 1.1 and 3.4. The focal mechanism solution for the main quake is consistent with a right lateral E-W oriented rupture, with north dip between 81 and 90 degrees. The epicenters spread in E-W direction over a 12 km long strip, with axis in the latitude 10º 28.7’ N, and between the longitudes 64º 8.5’ and 64º 15.2’W. This alignment corroborates an E-W oriented fault. A N-S depth profile of hypocenters corroborates the gathering around such a fault plane, with north dip of 85º ± 3º, emerging at surface around the north foot of the Caigüire hill, pointing out at the El Pilar fault segment at the north foot of the mentioned hill as the activated one. The presence of epicenters west from the Caigüire hill suggests that this fault segment does not blind at the north western corner of the hill; besides, it looks to extend as an active fault beneath the city westward from the hill. All secondary events occur west of the main epicentre. This atypical asymmetric distribution seems to corroborates the small barrier proposed by specialists at the north eastern corner of the Caigüire hill, 1.1 km East from the main epicenter, stopping ruptures towards that side. With respect to the geometrical and mechanical parameters of the main event, the empirical and seismological correlations give 7x10¹⁶ N-m of released seismic moment, 4x10¹² J of yielded energy, 34 bars of stress drop and 18 km² of rupture area with 13 cm of relative mean fault slip.

Keywords : Seismic swarm; Seismicity; El Pilar Fault; Cumaná; Caribbean Plate.