The 2009 M7.3 Earthquake Near Guanaja, Honduras

The M7.3 earthquake struck at 08:24 local time on 28 May 2009, with its epicenter located 46 km northwest of Guanaja in the Bay Islands of Honduras. The event originated at a depth of 19 km. This earthquake stands as the strongest recorded in the region since 2000. The Bay Islands lie along the tectonically active northern margin of Honduras, where the Caribbean Plate interacts with the North American Plate. Motion is accommodated primarily by the Swan Islands Transform Fault, a left-lateral strike-slip system that extends from the Mid-Cayman Spreading Center eastward toward the Honduran coast. This transform boundary produces frequent moderate-to-large earthquakes, with focal mechanisms typically showing horizontal shear consistent with plate-boundary slip. Geologically, the region formed through a combination of Cenozoic rifting and transcurrent faulting. The underlying basement consists of Paleozoic metamorphic rocks overlain by Cretaceous to Tertiary sedimentary and volcanic sequences. Ongoing oblique convergence and transform motion have created a series of pull-apart basins and restraining bends that localize seismicity offshore. The 19 km hypocentral depth places the 2009 rupture within the brittle upper crust, where accumulated strain on the Swan Islands Fault was released. Seismic history in the area reflects the steady slip rate of approximately 10–12 mm per year along the transform. While the 2009 event was the only M7+ earthquake in the immediate vicinity since 2000, smaller events occur regularly, underscoring the persistent hazard. Ground shaking was felt across the Bay Islands and parts of mainland Honduras and Belize, though detailed damage assessments remained limited due to the offshore location. Post-event analyses confirmed the rupture propagated along a segment of the Swan Islands Fault, releasing energy consistent with the long-term tectonic loading rate. No significant aftershock sequence above M6 was recorded, typical for moderate-sized transform earthquakes.

References

USGS Earthquake Catalog (event page for 2009-05-28 M7.3 Honduras) Global CMT Catalog (moment tensor solution) Honduras Geological Survey tectonic summaries