EVALUACIÓN PALEOSÍSMICA DEL SEGMENTO SAN FELIPE DE LA FALLA DE BOCONÓ (VENEZUELA NOROCCIDENTAL): ¿RESPONSABLE DEL TERREMOTO DEL 26 DE MARZO DE 1812?
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Universidad Industrial de Santander
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La Falla de Boconó (FB), estructura mayor de la frontera transpresiva entre las placas Caribe y Suramérica, presenta claras evidencias geomórficas diagnósticas de transcurrencia dextral cuaternaria en su sector más septentrional (Boc-e), ubicado a lo largo del margen noroeste de la depresión del río Yaracuy. Dos excavaciones paleosísmicas, ejecutadas en las localidades de Yaritagua (El Salto) y Quigua, en proximidad a Barquisimeto y San Felipe, respectivamente, en el año 2005, no sólo confirmaron su actividad tectónica durante el Holoceno, sino que determinaron que la FB es responsable igualmente del sismo destructor del 26 de marzo de 1812, el cual parece componerse de dos subeventos con epicentros macrosísmicos: uno en el mar al ONO de Caracas; y otro entre Barquisimeto y San Felipe, al pie de la sierra de Aroa, en el sector de la FB bajo estudio. Una grieta abierta rellena en El Salto, cuya edad resulta más joven que el año 1770 DC, es la evidencia de este sismo. Por su parte, FB en Quigua recurre con sismos Mw ≥ 7,0 cada 2.000-3.000 años, desconociéndose si ésta es toda su actividad sísmica y haciendo presumir que la deformación aquí debe estar distribuida en una amplia zona de deformación activa.
The Boconó Fault (BF), a major tectonic feature of the current transpressive plate boundary zone between the Caribbean and South America, exhibits a large number of Quaternary strike-slip landforms on its northernmost sector (Boc-e), along the NW edge of the Yaracuy tectonic depression. Two paleoseismic trenches, excavated in the vicinity of Yaritagua (El Salto) and Quigua, close to the cities of Barquisimeto and San Felipe respectively, in 2005, not only confirmed the Holocene activity of the BF in this fault portion, but also allowed the ascription to BF of the historical destructive earthquake of March 26th, 1812, which appears to have had two intensity centers: one offshore meizoseismal area WNW of Caracas; and the other one between Barquisimeto and San Felipe, at the foothills of the Aroa range, in the fault portion under study. An organic-rich filled open crack at El Salto trench, whose 14C age is younger than 1770 AD, is the evidence to this earthquake. On the other hand, Mw ≥ 7.0 earthquakes on the BF at Quigua recurs every 2000-3000 years. It is thought that present-day deformation along and across Boc-e may be accommodated by a wider zone.
The Boconó Fault (BF), a major tectonic feature of the current transpressive plate boundary zone between the Caribbean and South America, exhibits a large number of Quaternary strike-slip landforms on its northernmost sector (Boc-e), along the NW edge of the Yaracuy tectonic depression. Two paleoseismic trenches, excavated in the vicinity of Yaritagua (El Salto) and Quigua, close to the cities of Barquisimeto and San Felipe respectively, in 2005, not only confirmed the Holocene activity of the BF in this fault portion, but also allowed the ascription to BF of the historical destructive earthquake of March 26th, 1812, which appears to have had two intensity centers: one offshore meizoseismal area WNW of Caracas; and the other one between Barquisimeto and San Felipe, at the foothills of the Aroa range, in the fault portion under study. An organic-rich filled open crack at El Salto trench, whose 14C age is younger than 1770 AD, is the evidence to this earthquake. On the other hand, Mw ≥ 7.0 earthquakes on the BF at Quigua recurs every 2000-3000 years. It is thought that present-day deformation along and across Boc-e may be accommodated by a wider zone.
Keywords
Boconó fault, paleoseismicity, historical seismicity, Caracas 1812 earthquake, fifty-year rain, Yaracuy valley, Falla de Boconó, paleosismicidad, sismicidad histórica, sismo de Caracas de 1812, lluvia cincuentenaria, valle del Yaracuy