Seismic Hazards Along El Salvador's Pacific Coast

El Salvador occupies a tectonically active segment of the Pacific Ring of Fire, where the Cocos Plate subducts beneath the Caribbean Plate along the Middle America Trench. This convergent margin produces frequent large earthquakes, with hypocenters commonly located at depths of 30–80 km. The coastal zone south of Intipucá and Puerto El Triunfo lies directly above the seismogenic interface, resulting in high seismic hazard for the departments of La Unión, Usulután, and San Miguel. Instrumental records document several M7+ events since 2000. On 13 January 2001, a magnitude 7.7 earthquake struck 28 km SSW of Puerto El Triunfo at a depth of approximately 60 km. The event triggered widespread landslides in volcanic highlands and caused more than 800 fatalities. A second major shock of magnitude 7.3 occurred on 27 August 2012, centered 126 km south of Puerto El Triunfo. On 14 October 2014 at 03:51 UTC, another magnitude 7.3 earthquake took place 74 km south of Intipucá at a focal depth of 40 km. These three events cluster within an 82 km radius, illustrating the persistent strain accumulation and release along this portion of the subduction zone. Geological mapping shows that the overriding Caribbean Plate in this region consists of Neogene volcanic arcs and Quaternary sediments. The subducting Cocos Plate exhibits moderate to steep dip angles, facilitating megathrust ruptures that can exceed 100 km in length. Historical catalogs indicate recurrence intervals of 50–100 years for M7+ events, consistent with the observed sequence in 2001, 2012, and 2014. Tsunami risk remains moderate because most ruptures occur at intermediate depths rather than shallow megathrust patches directly beneath the trench. Ongoing monitoring by national and international networks confirms continued microseismicity along the plate interface. Ground-motion models calibrated to the 2001 and 2014 events predict peak accelerations exceeding 0.4 g within 50 km of the epicenters, sufficient to damage unreinforced masonry common in rural coastal communities. Updated probabilistic seismic hazard assessments incorporate these recent events and indicate that the 475-year return period ground motion along the coast reaches 0.6–0.8 g.

References

USGS Earthquake Catalog (event parameters 2001–2014)
Servicio Nacional de Estudios Territoriales (SNET), El Salvador seismic bulletins