Sismicidad y tectónica en el límite de placas del Caribe: noreste de Venezuela e Hispaniola

ANTONIO VILLASEÑOR HIDALGO

Abstract


The seismotectonics of two regions of the Caribbean plate boundary have been analyzed: northeastern Venezuela and Hispaniola. Both areas are characterized by a broad plate boundary zone, with complex geology and scattered seismicity. In order to better understand the seismotectonics of these areas, three types of seismic data have been used: seismograms of microearthquakes recorded by short period instruments; WWSSN seismograms of teleseisms; and historical seismograms of large pre-1963 earthquakes. The seismicity of northeastern Venezuela is first analyzed in terms of the results of a temporary microseismicity network. The main seismogenetic structure in the area is the El Pilar fault, proposed as the actual plate boundary between the Caribbean and continental South America. Focal mechanisms of microearthquakes show E-W right lateral strike-slip motion along the fault. Intermediate depth microearthquakes occur north of the peninsula of Paria, associated with the southern end of the subduction of Atlantic lithosphere under the Caribbean plate. Focal parameters of large northeastern Venezuela earthquakes have been calculated by inversion of teleseismic body wave waveforms. The results confirm that the El Pilar fault is the main source of seismogenetic deformation. Mechanisms of intermediate depth earthquakes of the Paria cluster show that active subduction is no longer taking place in northeastem Venezuela Finally, the 1946 Hispaniola earthquakes have been analyzed. This series includes the largest earthquake ocurred in the Caribbean plate boundary. The events of the series have been first relocated using teleseismic P and S wave times, by means of a leasts squares inversion procedure. Focal mechanisms have been calculated for the 4 largest earthquakes, using P, SV and SH polarities and SVlP and SV/SH amplitude ratios. The main shock (4 August 1946; MS = 7.8) mechanism represents thrusting of the northern terranes of the plate boundary zone over eastern Hispaniola as a consequence of a restraining bend.

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