GPS DERIVED VELOCITY FIELD IN WESTERN VENEZUELA: DEXTRAL SHEAR COMPONENT ASSOCIATED TO THE BOCONO FAULT AND CONVERGENT COMPONENT NORMAL TO THE ANDES

The deformation zone between the Caribbean and SouthAmerican plates broadens from less than 100km in northeastern Venezuela to more than 400 km in the west, bounded to the south by the northeast-striking Bocono fault system and to the north by an offshore trench that marks the southeast descent of the Caribbean plate beneath northern Colombia and northwestern Venezuela. New Global Positioning System (GPS) measurements within this region reveal that the 20 +/- 2mm/year of eastward displacement of the Caribbean plate relative to SouthAmerica in northeastern and north-central Venezuela is partitioned into a dextral shear velocity of 12 2mm/year along a locking line 14 +/- 4km beneath the surface expression of the Bocono. fault, with convergence normal to its northeast strike at 12 to 16mm/year. Of this convergence, similar to 1/3 concentrates in the Andean regions close to the Bocono fault and manifests itself geologically as a slip on a narrow belt of thrust faults nearly parallel to it, running similar to 25km away along both sides of the Bocono fault main trace. The convergent velocity field is not well constrained by the GPS data, but it is inferred that as much as 4mm/year occurs offshore northern Colombia.