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Smith Lecture: Caribbean-South American Plate Boundary Zone (Trinidad/Tobago) Active Deformation, Strain Partitioning, Fault Reactivation and Petroleum Geology Influence

John Weber, Grand Valley State
Friday, December 1, 2017
3:30-4:30 PM
1528 C.C. Little Building Map
This presentation will focus on observations and analyses of coseismic and interseismic aspects of the earthquake cycle on the major active faults in Trinidad and Tobago and how these relate to longer-term geomorphic and geological features.

Coseimic deformation: On 22 April 1997 the largest earthquake recorded in the Trinidad-Tobago segment of the Caribbean-South American plate boundary zone (Mw 6.7) ruptured a shallow, ENE striking, shallowly dipping (~28°) dextral-normal fault ~10 km south of Tobago. We studied this earthquake and related foreshocks and aftershocks. We derived coseismic offsets using GPS data, and modeled fault rupture and coseismic slip. Tobago moved NNE and subsided. This earthquake was anomalous and is of interest because: (1) its large component of normal slip and ENE strike are unexpected given the active E-W dextral shearing across the Caribbean-South American plate boundary zone, (2) it ruptured a normal fault plane with a low (~28°) dip angle, and (3) it reactivated and inverted the preexisting Tobago terrrane-South America ocean-continent (thrust) boundary that formed during early Tertiary oblique plate convergence.

Interseismic strain: We studied active faults in Trinidad and Tobago in the Caribbean-South American (CA-SA) transform plate boundary zone using episodic GPS (eGPS) data from 19 sites and continuous GPS (cGPS) data from 8 sites, and then modeling these data. Our best-fit model for interseismic fault slip requires: 12-15 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 ± 0.3mm/yr across the Soldado Fault in south Trinidad, and 3.5 ± 0.3 mm/yr of dextral shear on fault(s) between Trinidad and Tobago (see above). Faults in Trinidad show very little seismicity (1954-current from local network). Paleoseismic studies indicate that the CRF ruptured between 2710 and 500 yr. B.P. Together, these data suggest spatial and/or temporal fault segmentation on the CRF. The CRF marks a physical boundary between rocks associated with thermogenically generated petroleum and overpressured fluids in south and central Trinidad, from rocks containing only biogenic gas to the north, and a long string of active mud volcanoes align with the trace of the Soldado Fault along Trinidad’s south coast. Fluid (oil and gas) overpressure may thus cause the CRF and Soldado Faults to creep.
Building: C.C. Little Building
Event Type: Lecture / Discussion
Tags: Lecture
Source: Happening @ Michigan from Earth and Environmental Sciences