Abstract

A right-lateral strike-slip fault offset of a shallowly buried fluvial paleochannel is interpreted from three-dimensional (3-D) seismic data in the eastern offshore area of Trinidad. The fault represents the eastern offshore continuation of the main South America–Caribbean plate boundary zone in Trinidad, the Central Range fault zone. Previous global positioning system–based geodetic studies and trenching have shown that the 50-km-long on-land segment of the Central Range fault zone accommodates a significant part of the present-day interplate motion. The 3-D seismic data shown here reveal that the 60-km-long offshore continuation of the Central Range fault zone forms a prominent seafloor lineament and dextrally offsets a shallowly buried (83 m below sea level), late Quaternary fluvial channel by 322–506 m. Based on the eustatic sea-level curve, we infer that the channel began to be incised during the beginning of the Last Glacial Maximum ca. 30 ka and was subsequently offset by the Central Range fault zone. Using the offset amounts and our inferred age for the filled channel, we can estimate a long-term slip along the fault of 17–19 mm/yr for the Central Range fault zone. Because no documented earthquake has occurred on the Central Range since A.D. 1800, as much as 3.7 m of elastic strain may have accumulated on the Central Range fault zone that could be released by a future magnitude >M7.5 earthquake.

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