Earthquake Processes in the Lesser Antilles Subduction Zone
Open Access
- Author:
- Dunham, Audrey Margaret
- Area of Honors:
- Geosciences
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Dr. Maureen Feineman, Thesis Honors Advisor
Charles James Ammon, Thesis Supervisor - Keywords:
- Lesser Antilles Arc
Seismology
Earthquakes
Hazard - Abstract:
- The Lesser Antilles Subduction Zone forms the eastern boundaries between the Caribbean - North American, and the Caribbean - South American Plates. No large earthquakes have struck along this active convergent boundary in recent history, but a Mw 7.5-8.5 megathrust event ruptured the northern segment of the boundary on 08 February 1843. In this study, 68 earthquakes greater than Mw 4.8 that occurred between 1982 and 2016 are relocated using a surface-wave cross-correlation method to improve the relative locations of the available moderate-magnitude seismicity. Using the improved relative centroid locations, we are able to better identify several fault orientations and spatial relationships. Analysis of the fault and slip orientations helps clarify some aspects of the regional stress regime along the arc and within the subducting North and South American Plates. An original motivation for this study was to better constrain the plate boundary between the North and South American plates. The available seismicity is insufficient to this task. Even with improved relative locations, the data are too sparse and the boundary definition remains diffuse. Six moderate-magnitude earthquakes of the Mw 6.3 21 November 2004 normal-faulting sequence between Guadeloupe and Dominica align along a single trend striking roughly 325, consistent with the Global Centroid Moment Tensor (GCMT) faulting geometry estimates. Moderate-magnitude low-angle reverse faulting is common in the region (from Guadeloupe to the northern boundary), and is believed to have failed during the Great 1843 earthquake. The events are concentrated in the deeper segments of the plate boundary, but suggest a 120-130 km extent of seismogenic subduction in the 1843 segment. Seaward of the reverse faulting is a collection of strike-slip and oblique strike-strip (with a normal component) earthquakes, presumed to be in the subducting plate(s). These events suggest northwest-southeast compressive stresses in the oceanic North American Plate, that rotate to a more north-south direction beneath the South American Plate. Strike-slip earthquakes closer to the arc suggest an east-west oriented compressive stress. These are likely in the upper plate (based on comparisons with nearby reverse faulting earthquakes), but the pattern is not uniform. A shallow event (GCMT depth of 5 km) from 2014 exhibits a northeast-southwest compression, similar to strike slip events to the east. The larger strike-slip events within the oceanic lithosphere produced few aftershocks, similar to intraplate (and transform faulting) earthquakes that occur within the oceanic lithosphere globally. The strike-slip events in the upper plate, although fewer in number, have more typical aftershock patterns. By compiling the data and observations from earthquakes along the Lesser Antilles Subduction Zone, we can better understand the faulting mechanisms and hazards in the region.