Differences and similarities in the Cocos-North America and Cocos-Caribbean convergence, as revealed by seismic moment tensors

- We investigate seismic Moment tensors for Cocos-North America v. Cocos-Caribbean.
- There are significant differences in moment tensors between the two margins.
- Differences include number of earthquakes, magnitudes, azimuth of slip vectors.
- Azimuth of slip vectors suggest detachment of forearc in Central America.
- A new geometric model for the subducted slab is also found.

We investigate the differences and similarities in Cocos-North America and Cocos-Caribbean convergence, reflected by seismicity and seismic moment. We use well-located hypocenters of earthquakes in the convergence margin, as well as within the subducted slab. We sort these data by number of events in the two converging margins, and by their magnitudes. We also use this database to determine an improved geometric model of the subducted slab. We find a shallow-dipping subducting Cocos plate underneath North America and a steeper dip slab under the Caribbean plate. The transition between them appears to be smooth.Centroid Moment tensor solutions indicate that almost all of the thrust-faulting earthquakes along Cocos-North America take place at shallow depths. Normal-faulting events along this margin only take place to depths of 100 km. Thrust- and normal-faulting events take place at all depths along the Cocos-Caribbean margin. Cummulative scalar seismic moment for shallow, thrust-faulting events, is larger along Cocos-North America.T axes of intermediate-depth, normal- and thrust-faulting events show that the subducted Cocos plate is in maximum tension along the direction of maximum dip. Azimuth of earthquake slip vectors for shallow events along the Cocos-North America margin agree well with the direction of plate convergence. They do not agree along the Cocos-Caribbean margin; instead, agreement is found with Cocos-North America relative plate motion.Compensated Linear Vector Dipole (CLVD) ratio, which measures how different a seismic source is from a pure double-couple, along both margins is inversely proportional to scalar seismic moment, indicating that for larger magnitudes rupture is closer to a double-couple mechanism than at smaller moments.