Fault Creep and Strain Partitioning in Trinidad-Tobago: Geodetic Measurements, Models, and Origin of Creep

The expansion of geodetic networks and Earth observing systems has allowed for new understandings of continental transform faults, including the partitioning of relative plate motions between multiple active strands and fault behavior during the earthquake cycle. One important global observation is that some continental transform faults creep (i.e., slip aseismically) at a percentage of or even at the full relative plate motion rate. The Caribbean-South American plate boundary is a right-stepping, segmented, dextral continental transform system. We studied active faults in the Trinidad-Tobago segment of the Caribbean-South American plate boundary zone using a new GPS-derived horizontal velocity field, then modeled these data using a series of simple screw dislocation models. Our best-fit model for interseismic strain accumulation requires 13.4 ± 0.3 mm/yr of right-lateral movement and very shallow locking (0.2 ± 0.2 km), essentially creep, across the Central Range Fault (CRF), 3.4 ± 0.3 mm/yr across the South Coast Fault south of Trinidad, and 3.5 ± 0.3 mm/yr of dextral shear on fault(s) between Trinidad and Tobago. The CRF creeps along a physical boundary between rocks associated with thermogenically generated petroleum in south and central Trinidad and rocks containing only biogenic gas to the north. Fluid (oil and gas) overpressure, in addition to weak material in the fault core, likely causes CRF creep.