A systematic discrepancy exists between slip vectors of thrust fault earthquakes at the Lesser Antilles trench (LAT) and the predicted direction of North American‐Caribbean convergence. A possibility has been that the discrepancy resulted because neither was well constrained. Estimating Caribbean motion has been challenging owing to the limited data along the plate's complex boundaries. Similarly, earlier studies had few slip vectors because interplate thrust events are infrequent. To address these difficulties, we estimate a new Caribbean‐North America Euler vector using recently available GPS data from sites in the presumably stable interior of the Caribbean, and compare the predicted velocities to a larger set of slip vectors. The discrepancy persists, suggesting the northern Lesser Antilles forearc (NLAF) moves as a distinct entity from both the Caribbean and North America. For simplicity, we treat its motion as a coherent block, but because GPS sites are not within the NLAF, distributed deformation is also possible. Although there is no geologic evidence for the boundaries of the presumed NLAF block, GPS data show that the motions of Martinique, Barbados, and Trinidad are similar to that of the Caribbean, suggesting that none are on the NLAF block, and the southern LAT is weakly coupled.

[1] Earthquake focal mechanism solutions for 135 small-magnitude events are inverted for best fitting partial strain rate tensors that characterize contemporary strain in five areas that span the western margin of the Panama microplate in central Costa Rica. The results indicate the predominance of subhorizontal maximum stretching subparallel to the Middle America Trench (MAT) and provide constraints on the role of Cocos ridge collision at the MAT. The trajectory of maximum stretching changes $25°-45°over several tens of kilometers from the Central Costa Rica Deformed Belt (CCRDB) where it is nearly E-W to the area inboard of the Cocos ridge where it is NW-SE. This change suggests that background seismogenic deformation reflects the transition from the trailing edge of a fore-arc sliver to an area of the upper plate affected by ridge collision. This diffuse deformation may be localized, in part, on conjugate strike-slip faults of the CCRDB.

No abstract

No abstract

Plate boundary forces acting within the Cocos Plate that is being subducted at a rate of 8.5-9.0 cm a 21 towards N328E below the Caribbean Plate and the Panama microplate are found responsible for contemporaneous superimposed compressive, wrench and extensive fault patterns in Central Costa Rica. The stress inversion of fault-slip planes and focal mechanisms reveals a prevailing convergence-imposed N208 -458E almost horizontal compression. Ellipsoid R values [R ¼ (s 1 -s 2 )/(s 2 -s 3 )] in the range of 0.3-0.05 and 0.8-0.93 are responsible for the permutation of s 2 to s 3 and s 2 to s 1 , respectively, and show typical Andersonian configurations with one stress axis vertical or close to it. Coulomb failure stress (CFS) analysis reveals that up to 5 bars (0.5 MPa) of tectonic loading are being imposed on east-west thrusts and on critically oriented conjugate NW-and NE-trending strike-slip faults. Non-optimally oriented structures are potential targets for reactivation even with 2 bars (0.2 MPa) of load. Triggering and interaction with volcanic activity is highly suspected in one documented recent case. When the regional fault population was tested for its slip tendency (t/s n ), a good correlation with CFS results was found.

No abstract