Abstract

AUDEMARD M, Franck A et al. Renewed shallow seismicity in eastern Venezuela after the Cariaco July 1997 earthquake. bol.geol. [online]. 2019, vol.41, n.1, pp.117-132. ISSN 0120-0283.  https://doi.org/10.18273/revbol.v41nl-2019006.

This research shows a clear increase in shallow seismicity in the 21st century, after the Cariaco July 09th, 1997 earthquake, from the qualitative-quantitative analysis of a more than 30-year-long record of instrumental seismicity (1983-2017). The seismic activity increase is not randomly distributed but comes in patches, which align along with the El Pilar (FEP), Los Bajos (FLB), El Soldado (FES) and Bohordal (FB) faults, very particularly with their portions close or within the Paria gulf. Equally, this seismicity occurs South of the easternmost south-dipping FEP segment, and East of the San Juan Graben fault system. No major or destructive historical and instrumental earthquake is associated to this segment for the last 520 years. From the assumption that the contiguous-to-the-west FEP segment recurs roughly every 350-450 years with an Mw +7.0 event, we invoke that stress transfer from the recently-broken 1997 segment is responsible for the unusually high crustal seismicity happening in this 21st century, activating the easternmost FEP segment as well as the mechanically interconnected southern faults. This could lead to a major destructive (eventually tsunamigenic) earthquake on FEP in the near future. On the other hand, the higher creep (50 over 40%) and slower slip rate (10 vs 12 mm/yr) of the easternmost segment than its western contiguous segment could account for the longer return period; longer than the 350-450 year return period determined from paleoseismic trench studies undertaken across the 1997 earthquake rupture.

Keywords : Sismicidad cortical; Red Sismológica Nacional de Venezuela; Transferencia de esfuerzos; Desplazamiento asísmico; Repteo; Amenaza.; Shallow seismicity; Venezuelan Seismological Network; Stress transfer; Aseismic slip; Creep; Hazard.

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