Strain Partitioning and Interseismic Fault Behavior Along the Caribbean‐South American Transform Plate Boundary

Abstract

We combine Global Positioning System and Interferometric Synthetic Aperture Radar (InSAR) data to characterize the interseismic behavior (i.e., locked or creeping), and strain partitioning for the faults along the Caribbean‐South American transform plate boundary. Interseismic strain is distributed mainly on three faults, the San Sebastian, El Pilar, and Central Range faults, but partitioning occurs across multiple faults in the west (San Sebastian and La Victoria faults) and east (Sub‐Tobago Terrane, Central Range, and South Coast faults). In northern Venezuela, slip is partitioned on the San Sebastian (16.4 ± 1.7 mm/yr) and La Victoria (4.3 ± 0.9 mm/yr) faults. In north‐eastern Venezuela, the El Pilar fault accommodates slip at a rate of 18.6 ± 1.8 mm/yr. In Trinidad and Tobago, slip is partitioned between the Sub‐Tobago Terrane (3.0 ± 0.1 mm/yr), Central Range (14.5 ± 2.0 mm/yr), and South Coast (3.0 ± 0.1 mm/yr) faults. The La Victoria, San Sebastian, the western El Pilar segment, and Sub‐Tobago Terrane faults are locked to depths of 16.2 ± 4.0 km, 7.7 ± 5.2 km, 6.7 ± 2.8 km, and 8.0 ± 0.2 km, respectively. The eastern segment of the El Pilar, the Central Range, and the South Coast faults all creep. Our new InSAR results indicate that the entire Central Range Fault is creeping. The locked western segment of this transform plate boundary is capable of producing a Mw 8 earthquake, which is a significant finding regarding seismic hazard and risk.

The Geodetic Signature of Bookshelf Faulting in Nicaragua

“…Daily GPS static positions were produced using the methods of Higgins et al. (2021). A minimum of 2.5 years of daily positions (see Blewitt & Lavallée, 2002) for episodic GPS (eGPS) and continuous GPS (cGPS) were used to determine the velocity field (Table S1 in Supporting Information S1).…”

“…We inverted the GPS‐derived horizontal velocity profiles, for a single, vertical, margin‐parallel fault using the analytical elastic dislocation model (Savage & Burford, 1973), solving for the fault offset (position along profile), interseismic slip deficit rate, and locking depth. We employed a hybrid Monte Carlo strategy, where velocities were perturbed by random sampling within the range of the observed velocities and their uncertainties and the solution sought using the fmincon minimizer in the Matlab software (Higgins et al., 2021). Uncertainties were calculated from the resulting probability distributions (Figures S1 and S2 in Supporting Information S1).…”

“…To gain insight into deformation across the CAFA-CA plate boundary zone, we developed a new horizontal velocity field for northern Nicaragua using both continuous (29 stations) and campaign-style episodic (35 stations) GPS data (Tables S2 and S3 in Supporting Information S1). Daily GPS static positions were produced using the methods of Higgins et al (2021). A minimum of 2.5 years of daily positions (see Blewitt & Lavallée, 2002) for episodic GPS (eGPS) and continuous GPS (cGPS) were used to determine the velocity field (Table S1 in Supporting Information S1).…”