Global Positioning System (GPS) data from eight sites on the Caribbean plate and five sites on the South American plate were inverted to derive an angular velocity vector describing present-day relative plate motion. Both the Caribbean and South American velocity data fit rigid-plate models to within ؎1-2 mm/yr, the GPS velocity uncertainty. The Caribbean plate moves approximately due east relative to South America at a rate of ϳ20 mm/yr along most of the plate boundary, significantly faster than the NUVEL-1A model prediction, but with similar azimuth. Pure wrenching is concentrated along the approximately east-striking, seismic, El Pilar fault in Venezuela. In contrast, transpression occurs along the 068؇-trending Central Range (Warm Springs) fault in Trinidad, which is aseismic, possibly locked, and oblique to local plate motion.

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Based on 13 new fault plane solutions and published seismological, geological, and geophysical data, we interpret the deformation along the Pacific‐North American plate margin in the eastern Gulf of Alaska. Three major tectonic units can be distinguished: (1) the North American plate, (2) the Pacific plate, and (3) a belt of mobile borderland terranes. The Pacific plate moves in a NNW direction at rates of about 6 cm/yr in relation to the North American plate. That motion results in mostly right‐lateral strike slip at the Queen Charlotte‐Fairweather fault system, a well‐known observation. A new finding,however, is that a small component (∼1 cm/yr) of convergence may also be present which results in minor subduction of the oceanic plate beneath portions of the continental margin. Heretofore the Queen Charlotte‐Fairweather fault zone and associated continental margin was interpreted as a classical, pure transform boundary. The Yakutat block, a borderland terrane about 400 km long and 100 to 200 km wide, is carried passively by the Pacific plate except that the block slowly overrides this plate at about 1 cm/yr. This motion is taken up by almost pure thrust faulting in a southwesterly direction along a 400‐km long SE striking shelf edge structure. At its NW edge the Yakutat block is in turn being thrust beneath the North American plate along the Pamplona zone‐Icy Bay lineament. The underthrusting of the Yakutat block results in a major orogeny, crustal shortening and uplift of the Chugach‐St. Elias range. The effects of this collision may extend as far as 500 km inland and cause some deformation at the Denali fault in the central Alaska Range. Subduction of the Pacific plate beneath the colliding margin appears responsible for development of an active volcanic arc up to 300 km inland which trends SE from the Wrangell Mountains to Yukon Territory, Canada, and perhaps to Mt. Edgecumbe volcano in southeast Alaska. The tectonic model proposed implies a high seismic hazard for the Queen Charlotte, Fairweather, and Chugach‐St. Elias fault systems. At these fault zones we estimate recurrence times for great events of about 100 years, but they may vary between 50 and 200 years. A temporarily very high potential for a great earthquake has been determined for the ‘Yakataga seismic gap’ located between Icy Bay and Kayak Island. Large or great thrust earthquakes on the detachment fault underlying the entire Yakutat wedge also appear possible but may only occur infrequently. Their recurrence times are estimated to be several

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