The 2017 Matzaco Earthquake and Regional Seismicity in Mexico

The magnitude 7.1 earthquake that struck 1 km south of Matzaco, Mexico, on 19 September 2017 at 18:14 local time originated at a depth of 48 km. This event stands as the sole M7.1 or greater earthquake recorded in the region since 1 January 2000, underscoring its significance within the local seismic record.

Central Mexico occupies a tectonically active zone along the Pacific Ring of Fire. Here, the oceanic Cocos Plate converges with and subducts beneath the continental North American Plate at rates of approximately 6–7 cm per year. This subduction process generates intense compressional stresses that accumulate along the plate interface and within the overriding crust, producing both shallow crustal and intermediate-depth intraslab earthquakes. The 48 km focal depth of the Matzaco event places it within the intraslab environment, where bending and dehydration of the descending slab can trigger brittle failure.

Historical seismicity in southern and central Mexico reflects this ongoing subduction. Notable predecessors include the 19 September 1985 Michoacán earthquake (M8.0), which caused widespread damage in Mexico City due to long-period ground motions amplified by the lake-bed sediments of the former Lake Texcoco. Earlier events, such as the 28 July 1957 M7.8 earthquake near Acapulco, similarly demonstrated the capacity for large-magnitude ruptures along the Middle America Trench. These episodes illustrate a recurring pattern of strain release that has shaped both the landscape and building practices across the region.

The 2017 Matzaco earthquake fits within this continuum. Its timing on the anniversary of the 1985 event drew immediate public attention, yet its geological setting remained consistent with the established subduction framework. Post-event analyses confirmed that the rupture occurred on a steeply dipping fault plane within the subducting slab rather than on the plate interface itself, a characteristic shared with other moderate-to-large intraslab events in the Mexican subduction zone.

Ongoing monitoring by national and international seismic networks continues to track aftershock sequences and background seismicity in the area. These observations reinforce the understanding that central Mexico will experience further earthquakes as plate convergence persists. Preparedness measures, including updated building codes and early-warning systems, have evolved in response to both the 1985 and 2017 events, aiming to mitigate future impacts in this densely populated and geologically dynamic region.

References

United States Geological Survey Earthquake Catalog Servicio Sismológico Nacional, Universidad Nacional Autónoma de México