Revised seismic history of the El Pilar fault,Northeastern Venezuela,from the Cariaco 1997 earthquake and recent preliminary paleoseismic results |
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| Authors: | Franck A Audemard |
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| Institution: | (1) Venezuelan Foundation for Seismological Research—FUNVISIS, Apartado postal 76.880, Caracas, 1070-A, Venezuela |
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| Abstract: | In light of the July 9, 1997, Cariaco earthquake, it is clearly understood now that damage in the city of Cumaná – located
in northeastern Venezuela and frequently destroyed by the largest earthquakes since the first recorded event in 1530 – is
strongly enhanced by poor soil conditions that, in turn, are responsible for site amplification and widespread earthquake-induced
effects. Therefore, most previous macroseismic studies of historical earthquakes must be revaluated because those localized
high-intensity values at Cumaná surely led to the misestimation of past epicenters. Preliminary paleoseismic results, gathered
at three exploratory trenches dug across the surface break of the Cariaco 1997 earthquake in 1998, allow us to associate the
1684 earthquake with this recently ruptured fault segment that extends between the towns of San Antonio del Golfo and Río
Casanay (roughly between the two gulfs of Cariaco and Paria, state of Sucre). Other major results from the reassessment of
the seismic history of this fault are: (a) the 1766 event seems to have generated in a different source to the El Pilar fault
because the size of the felt area suggests that it is an intermediate-depth earthquake; (b) damage to Cumaná produced by the
1797 event suggests that this was a local earthquake, perhaps equivalent to the 1929 earthquake, which ruptured for some 30 km
just east of Cumaná into the Gulf of Cariaco; and (c) seismogenic association of the 1530 and 1853 earthquakes still remains
unclear but it is very likely that these ruptures occurred offshore, as suggested by the rather large tsunami waves that both
events have generated, placing their hypocenters west of Cumaná in the Cariaco Trough. This reassessment also sheds light
into the El Pilar fault segmentation and the behavior of its seismogenic barriers through time. |
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| Keywords: | Historical seismicity Paleoseismology Recurrence Segmentation El Pilar fault Caribbean |
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